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DIY Stompboxes => Building your own stompbox => Topic started by: whomeno on October 11, 2018, 11:24:12 AM

Title: help with oscilloscope model 34
Post by: whomeno on October 11, 2018, 11:24:12 AM
ok replaced the 1v2 tube. no line on scope tried all settings. what should I look for now.
the only tube i could not test was the 6af

Schmatic

(https://i.postimg.cc/phK5bYrS/bh34schem.jpg) (https://postimg.cc/phK5bYrS)
Title: Re: help with oscilloscope model 34
Post by: PRR on October 11, 2018, 02:25:38 PM
Generally troubleshooting involves Voltage Checks.

BUT this beast has 2,000 Volts at potentially lethal charge.

Are you experienced enough to work in there and not be killed?

(It isn't always the electric shock. I picked up a 20KV CRT, it "stung me", I fell down and bumped my head on the bench.)

While I am fond of tube 'scopes, and free 'scopes, I an NOT fond of repairing them. Especially today when you can get a pocket-'scope kit for far under $100. Cheaper than a  concussion or a funeral.
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 11, 2018, 03:11:21 PM
I have worked on older projection tvs and got them working, never worked on a scope. my dmm is only rated for 600. did not get test leads for the 1s14 I got with the scope. tring to find the right banana plug for leads, they are small.
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 11, 2018, 04:55:17 PM
OK we don't know  if there's a problem with the HV (~1200V) or not.

Don't put your meter across the 1200V it will get zapped.   There's a trick to measure this but normally you don't have to measure it.  It is often checked by measuring current by measuring the voltage across R62.  Don't worry for now deal with that later.

There's many things to go wrong and it only takes one to stuff it up.
So it's best to go through each section one by one.

For reference:
http://steptorun.com/shop/icon/2/EX-3-0022.jpg

Power:
- Are the heaters on all the tubes lighting-up?  (Including the Display you should see a glow at the back of the tube.)    Can't remember if you can see the heater working on 1v2 or not.
- Check all DC power rails

Check Horizontal amps:
- Switch the sweep selector to Horizontal input  (EXT on the Sweep Selector *NOT* the Sync Control).
-  Measure the voltages on the plates of V6A and V6B. 
   Check the  the Horizontal Position makes the voltage go up and down on each.
   When one plate goes up the other should goes down and the two voltages should be
   more or less equal with the Horizontal Position roughly in the mid position.

Check Vertical amps:
- Set the Vertical Sensitivity to 50V
- Measure the voltages on the plates V2A and V2B
   Check the  the Vertical Position makes the voltage go up and down on each.
   When one plate goes up the other should goes down and the two voltages should be
   more or less equal with the Vertical  Position roughly in the mid position.
-  Wouldn't hurt to check plate voltages on V1A, V1B, V1C


[EDIT:
FYI:  With the Horizontal mode set as above you will no longer get a line.  You will get a dot which you can move up/down left/right with the Vertical and Horizontal position controls.

Don't let the dot stay in one spot it will damage the screen.   Keep the intensity down on this mode so you can just see it.   Only turn up the intensity while trying to find the dot.
]
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 11, 2018, 05:06:30 PM
Quote
BUT this beast has 2,000 Volts at potentially lethal charge.

Based on the cap voltages I'm guessing 1.2kV.  1.2kV wasn't uncommon in simple CRO's of the day.   Better models were 2.5kV.  More modern models are 8kV or so.
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 11, 2018, 05:34:52 PM
The manual in the other thread was for the transistor version (unless I've missed something).

Here's a link to a tube version which is similar but not the same (eg. V1 is split into V1 and V2).
Until I find an exact match it can be used as a guide.  The main point is it has some test voltages marked on it.  They should be a good ball park to get you started.
http://www.heathkit.nu/O-12_mod_schematic_2428.png

Non-mod version:
https://elektrotanya.com/heathkit_o12_oscilloscope_sch.pdf/download.html
https://elektrotanya.com/PREVIEWS/38933510/23432455/heathkit/heathkit_o12_oscilloscope_sch.pdf_1.png
Title: Re: help with oscilloscope model 34
Post by: PRR on October 11, 2018, 05:42:24 PM
> I'm guessing 1.2kV.

His 'scope plan shows 1600V AC.

Your similar plan shows 1040VAC making 1340VDC, as expected from *1.414 - losses.

I will not argue the exact value; it is not critical either for operation or shock. 500V would "work" at lower brightness and focus; and still be dangerous. As you say, he wants "some" current at the *bottom* of some handy divider where the KV is few-V.
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 11, 2018, 05:59:59 PM
Quote
His 'scope plan shows 1600V AC.
I only see that as the 1600V cap voltage.
1.2kV is a number I've seen kicking around a lot (the new schem actually shows 1200V at the display pin).
Anyway the last couple of schematics I posted shows some more precise voltages, unfortunately for other models, but there's a good chance they kept the same transformer.

Quote
As you say, he wants "some" current at the *bottom* of some handy divider where the KV is few-V.
It's common to *set* the beam current as part of calibration. Which is usually done with a pot.
Title: Re: help with oscilloscope model 34
Post by: thermionix on October 11, 2018, 07:58:13 PM
Which is usually done with pot.
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 11, 2018, 08:16:11 PM
Quote
Which is usually done with pot.
That's so you get twice the buzz if you slip  :o.
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 11, 2018, 08:22:14 PM
ok here are pics.  which 12au7 should i be testing for the horiz  part and which one for the other? there are 3 12au7's   all tubes lighting up display also



(https://i.postimg.cc/zbBYG6QH/20181011-201256.jpg) (https://postimg.cc/zbBYG6QH)




(https://i.postimg.cc/V00yjMmY/20181011-201321.jpg) (https://postimg.cc/V00yjMmY)





(https://i.postimg.cc/PLS09KqX/20181011-201413.jpg) (https://postimg.cc/PLS09KqX)
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 11, 2018, 08:59:31 PM
ok they are marked. meter set on 600
v6A  69 pin 1
v6b   32  pin 6
They do not move when switch is moved
v2 a   65   pin1
v2b    45   pin6
dose not move with switch
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 11, 2018, 09:16:48 PM
Quote
ok they are marked. meter set on 600
v6A  69 pin 1
v6b   32  pin 6
They do not move when switch is moved
v2 a   65   pin1
v2b    45   pin6
dose not move with switch
They look low.  Should be 260V and 280V.

Have a look at the Heathkit schematics I posted a few posts ago (reply #5).
They have voltages marked on the schematic.
Start by measuring the voltages in the bottom right hand corner of the schematic.
They have  labels A, B, C etc.

These ones are probably the most important to check at the moment:
G_semicircle  +350V
G_triangle  +385V
G_square   approx +430V

Then,
A +105V
B +110V
C +120V
D +115V


Actually the Heathkit circuit is a little different.  Here's my best guess at the voltages:

(https://i.postimg.cc/fJC90ZSg/bh34-oscilloscope-voltages-1.png) (https://postimg.cc/fJC90ZSg)

Use the caps and the resistors on the supply to help you find them on the actual unit.  When you measure the voltages make sure you measure the correct side of the resistor.
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 11, 2018, 10:22:04 PM
going by the schmatic v8 pin 1 & 6 should have power, but on scope not hooked up  pins 4- 5- 9 are used.


I have 4 red 2 white and 2 green coming from power supply.
the 2 white go to v8  4  & 5 both at 146v
v7 pin 7 is 68v
the red wires has nothing over 70v
(https://i.postimg.cc/ThPR9dxb/20181011-222035.jpg) (https://postimg.cc/ThPR9dxb)
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 11, 2018, 10:33:12 PM
if you look at the schmatic i posted thats how v7 and v8 is wired. i am charging up my camera to take better pics for you. I am trying my best to follow along with you. i can understand the schmatic but it don't make sense the way the unit is wired.
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 11, 2018, 11:32:06 PM
here are better pics


(https://i.postimg.cc/GBSLyVfY/100-0757.jpg) (https://postimg.cc/GBSLyVfY)







(https://i.postimg.cc/mzvTdMBg/100-0758.jpg) (https://postimg.cc/mzvTdMBg)









(https://i.postimg.cc/RNzMKcgP/100-0759.jpg) (https://postimg.cc/RNzMKcgP)
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 11, 2018, 11:50:01 PM
I've annotated your previous pic with the voltage points and some part values.
To me it looks like C33C and C33D are swapped on the built version; assuming we go A, B, C, D
counter-clockwise on the caps. (I'm just mentioning that. It is how it is drawn in my pic and it's fine like that.)

(https://i.postimg.cc/QHn0WvPs/psu-points-on-chassis.png) (https://postimg.cc/QHn0WvPs)

Give me a chance to look over your new pics.
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 12, 2018, 12:02:13 AM
Quote
I have 4 red 2 white and 2 green coming from power supply.
the 2 white go to v8  4  & 5 both at 146v
v7 pin 7 is 68v
the red wires has nothing over 70v
Those are really weird voltages.

I think you need to measure:
- The heater voltage, should be 6.3V AC between the green wires.
- The voltage on pins 1 of V7 to ground and pin 6 of V7 to ground, should be maybe 330V AC.
=================
Ahhhh
Quote
v8  4  & 5 both at 146v

Don't measure stuff around V8 with your multimeter.  V7 is OK not V8!
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 12, 2018, 12:30:15 AM
After that, pull out V8 and remeasure the voltage on pin 1 and pin 6 of V7.
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 12, 2018, 01:00:02 AM
between green wires 6.6 v
v7 pin 1 395 v   pin6  395v

pulled v8
v7    pin1 395v           pin6 395v
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 12, 2018, 01:18:12 AM
Quote
between green wires 6.6 v
v7 pin 1 395 v   pin6  395v

pulled v8
v7    pin1 395v           pin6 395v

That's a relief.  Those look good.

We need to work out why the voltage on pin 7 of V7 is low.
Some possibilities:
- V7 has a problem.
- some fault is pulling down the voltage
- one of the parts of cap C33 has a problem

Put V8 back in.  And measure the voltage across R54 and R55.
That will tell how much current is flowing down each of them.
If the current is small and the voltage on pin 7 of V7 is low
then maybe V7 is stuffed or C33A has a "short".




Title: Re: help with oscilloscope model 34
Post by: whomeno on October 12, 2018, 01:57:41 AM
just rechecked v7 pin 7 953v
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 12, 2018, 02:01:41 AM
Quote
just rechecked v7 pin 7 953v
V7?  953V is really high.  Are you sure it's not 453V?

What about the voltages across R54 and R55.
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 12, 2018, 02:14:01 AM
r54 right by v7 on strip end to end 108

r55 by v2 on strip end to end 79

rechecked v6a pin 1   658    v6b  pin 6 330
v2a  pin 1  724  v2b  pin 6  524

but they do not move when switch is moved

yes pin 7 is 953 on v7
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 12, 2018, 02:22:12 AM
Quote
yes pin 7 is 953 on v7

I can't believe it is that high.  I think you damaged your multimeter connecting it to V8.

If you have another meter try using that.

If you have some voltage sources or equipment with known the voltages,
check your meter can measure those voltages correctly.   The problem might only
show up on the highest voltage range.




Title: Re: help with oscilloscope model 34
Post by: whomeno on October 12, 2018, 02:31:07 AM
meter seems ok checked input v at 120 v
i did not have a good ground when i hit v8
have good ground now
only meter i have
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 12, 2018, 02:38:34 AM
when you wanted me to read voltage across r54 r55 did you want it from ground to one end then the other?
or a lead on each end of resistor?
if i measure from ground to each end
R54
1 end 833   2nd end  947

R55
1 end  700  2nd end  782
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 12, 2018, 02:42:53 AM
Quote
meter seems ok checked input v at 120 v
i did not have a good ground when i hit v8
have good ground now
only meter i have

Do you still get    V7 pin 1 395 VAC  and V7 pin6  395 VAC?

I'm having trouble trying to work out how V7 pin gets to 953V.   It should be about 450V.

If the meter is OK then I suspect the one of the power rails from V8 (V8 pin 1, V8 pin 9, C30, C31, R63, R61, R62) has shorted to V7 pin 7.
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 12, 2018, 02:43:58 AM
Quote
when you wanted me to read voltage across r54 r55 did you want it from ground to one end then the other?
or a lead on each end of resistor?
Across each resistor.   The idea is it lets you work out the current through each resistor V/R.

Title: Re: help with oscilloscope model 34
Post by: whomeno on October 12, 2018, 02:44:53 AM
yes v7 pins are the same 1   395  6   395
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 12, 2018, 02:49:01 AM
Quote
yes v7 pins are the same 1   395  6   395
OK.  So that says the transformer is OK.

Try pulling out V8 and remeasuring  V7 pin 7.

I'm worried about running the unit with 953V on the 450V caps they will blow up.
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 12, 2018, 02:49:55 AM
dumb question how can a meter set to 600v measure 900 volts
meter is a utl 33
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 12, 2018, 02:51:23 AM
with v8 out still at 955
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 12, 2018, 03:06:17 AM
Quote
dumb question how can a meter set to 600v measure 900 volts
Well it depends on the meter. It could measure correctly but is stressing out the internal components.   Or it could be measuring wrong and the overload somehow isn't working.

Quote
with v8 out still at 955
Pulling V8 removes any chance of the 1200V rail shorting to the 430V rail and producing crazy high voltages.

I'm having trouble understanding how a transformer is producing 395VAC is getting to 955V DC.  The DC cannot (should not) get above 395V * 1.41 = 559V.   The 6X4 has voltage drops so the DC should be somewhat less than that.

I'm not sure how keen you are but at this point I would make a voltage divider probe:

  [Probe input +]  ----  10M  ---- 10 M  -----+-----  1M  --- o----  [Probe input -]

  [Probe input +] connects to the point to be measured in the circuit.
  [Probe input -]  connects to the circuit ground.
  The point + goes to the meter + and the point o goes to the meter -.
  This will divide the measured voltage down to about 1/23.
  So 955V should drop to 41.5V
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 12, 2018, 03:39:17 AM
When I compare the voltages across the resistors with the difference of the voltage on each side of the resistor  the results are fairly consistent.

Quote
r54 right by v7 on strip end to end 108
r55 by v2 on strip end to end 79

R54  1 end 833   2nd end  947
R55 1 end  700  2nd end  782
947 - 833 = 114; only 6% higher than across resistor
782 - 700 = 82;   only 4% higher than across resistor

*IF* the meter is measuring OK on the low range then the measurements on the high range look OK.

I still can't explain the disagreement between the AC voltage and DC voltages.
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 12, 2018, 04:01:53 AM
I made probe just as you said retested v7 pin 7 it droped it to 14.5v
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 12, 2018, 04:29:58 AM
More trouble, I tried to find the input impedance of your meter (UTL33T) and the manual doesn't state it - ahhh!

Is there any chance you could replace 1M in the probe circuit with 100k? and repeat the test.   That helps remove the uncertainty of the meter impedance.   The multiplying factor will then be between x203 to x221;  ie. 10% uncertainty.

Anyway,

If your meter is 10 M ohm input impedance the real voltage is 23 times what you measured,

    V(V7 pin 7)  = 23 * 14.5 = 334V

If your meter was 1M ohm input impedance the real voltage is 41 times what you measured,

    V(V7 pin 7) = 41 * 14.5 = 596V

So despite the uncertainty of the measurement of 334V to 596V we definitely aren't getting 950V.  So something weird might be happening with the meter.

Based on that, it's looking like your meter is doing something weird on the 600V *DC* range.
But not I can't explain why the difference are only 10% out.

Title: Re: help with oscilloscope model 34
Post by: whomeno on October 12, 2018, 04:35:35 AM
will do it now
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 12, 2018, 04:39:04 AM
If you have a 9V supply or a battery good idea to measure it *without* the voltage probe.
We need to measure something we really know.
I'm pretty confused about what's going on ATM.
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 12, 2018, 04:46:41 AM
new battery is 9.56
redid probe with 100k retested at 3.2v

don't you mean ac 600
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 12, 2018, 04:55:29 AM
I am so sorry I was using ac side not dc v7 pin 7 is 429v dc

v6 pin 1 300v   dose change
pin6  144v


v2 1   324v pin2  234v
dose not change much
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 12, 2018, 05:03:44 AM
still no line or dot to be found
with the probe it is 1.8v from 429
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 12, 2018, 05:27:59 AM
in the schmatic  v4 is a 6j6  my v4 is a 12au7
in the schmatic v7 is a 12au7  my v7 is a 6x4
will this matter?
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 12, 2018, 05:33:33 AM
OK cool that's starting to make more sense.

Quote
still no line or dot to be found
You won't see a dot until both V2 and V6 balance,
 in that
Voltages V2 pin 1 = Voltage V2 pin 6, and
Voltage V6 pin 1 = Voltage V6 pin pin 6.

I suspect V6 is a good place to start.      The aim is to get Voltage V6 pin 1 = Voltage V6 pin pin 6 when the Horizontal position is set to about half way.  When you check the voltages make sure the width control (R44) is fully counter clockwise (ie the wiper at position 1 on the schematic).

It might a good idea to power the unit down, discharge all the caps, pull out V6, then measure the values of R53, R52, R51.  If the values have drifted it might cause problems.

Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 12, 2018, 05:36:16 AM
Quote
in the schmatic  v4 is a 6j6  my v4 is a 12au7
in the schmatic v7 is a 12au7  my v7 is a 6x4
will this matter?
Use the schematic you posted.
From what I can see it matches your unit.
The Heathkit schematics I posted are only good to get an idea of the voltages because your schematic doesn't show any voltages.

Title: Re: help with oscilloscope model 34
Post by: whomeno on October 12, 2018, 06:00:55 AM
ok
R53  27K    34.8
R52  27K     36
R51  10K      11.1

v6
p1 226
p6  224
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 12, 2018, 06:46:11 AM
how close dose pin 1 and 6 need to be?
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 12, 2018, 08:24:53 AM
Quote
ok
R53  27K    34.8
R52  27K     36
R51  10K      11.1

That shows the resistors have drifted quite a bit. Luckily R53 and R52 have drifted equally.
It's not uncommon for old resistors to go off.  What it does mean is there's probably a
lot of other resistors in the unit that have drifted like that and you have to be aware that
the values of resistors might not be what you think they are.

Quote
v6
p1 226
p6  224
Those are quite good readings.

Quote
how close dose pin 1 and 6 need to be?
At one extreme of the horizontal position control you should be able to have one higher than the other at one extreme and at the other extreme the lower one should then become higher than the higher one.  In the middle there is a place where they are about equal.    In other words if you measure the voltage *between* pins 1 and pin 6 you will see a negative voltage, zero voltage, and a positive voltage as you adjust the horizontal position.

The same idea applies with V2 and the vertical position control.  You should measure the resistances R21, R22, R23, R24, R25, R26, R27 to see if there are any way-off resistances.

Once you can get equal voltages on pin 1 and pin 6 of V2 it shouldn't be too hard to get a dot.
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 12, 2018, 02:54:42 PM
ok I,m back
here is my findings so far
R21 1.2k = 1.26
R22 2.7k= 2.65
R23  1K  =  1.24
R24  5.6K = 5.48
R25  2.7K = 2.60
R26  1K    = 1.26
R27  5.6K = 5.58
v2 pin1 =332   pin6 = 309

could it be the main tube is bad?
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 12, 2018, 03:18:31 PM
ok v6 is working fine

now to get v2 going
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 12, 2018, 03:28:25 PM
ok v2 pin1 =264
 pin6 = 250
but moving switch dose nothing
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 12, 2018, 03:53:25 PM
Quote
ok v6 is working fine
Great.

Quote
ok v2 pin1 =264
 pin6 = 250
but moving switch dose nothing
The thing that changes the voltages on V2 is the Vertical Position pot.

The pot is R19 on the schematic and has four wires.   The middle wire of the group of three pot connections is marked "2" on the schematic.   Make sure there is a wire from Vertical Pot  "pin 2"  to V2 pin 2.
The voltage on V2 pin 2 should vary with the Vertical Postion pot from about 30V to 45V.
The voltage between V2 pin 2 and V2 pin 7 should be adjustable  from -7.5 to -7.5V.
(The voltage on V2 pin 7 cannot be measure directly because the multimeter loading will change the measurement. Also excessive leakage on V2 pin 7 can shift the voltage.)

Title: Re: help with oscilloscope model 34
Post by: whomeno on October 12, 2018, 04:13:38 PM
ok wire is there to pins 2. switch moves voltage on v2 pin 2
how do i measure pin 7 if i can't do it directly?
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 12, 2018, 04:15:46 PM
v2 pin 2 = 34v to 54v
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 12, 2018, 04:23:49 PM
Quote
how do i measure pin 7 if i can't do it directly?
Just measure the difference between pin V2 pin 2 and V2 pin 7; see previous post.
The thing that is important it to get + and - voltage when you vary the Vertical Position pot.

Quote
v2 pin 2 = 34v to 54v
That is probably OK. 
Next do the voltage difference test.
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 12, 2018, 04:30:37 PM
ok with switch at 0 pin2 54.2  pin7  5.05
switch at 10  pin2  35.3          pin 7   6.6
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 12, 2018, 04:33:56 PM
R17  3.3m  = 3.7m
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 12, 2018, 04:35:53 PM
Quote
ok with switch at 0 pin2 54.2  pin7  5.05
switch at 10  pin2  35.3          pin 7   6.6
You need to measure the voltage difference by putting the probe on pin 7 and on pin 2 at the same time then measure the voltage with the Vertical Position pot at each extreme.

(Notice that the pin 7 is low because the multimeter loads it down.  To me it looks like it is loading it down a lot.)
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 12, 2018, 04:37:02 PM
Quote
R17  3.3m  = 3.7m
That's good to know. It looks OK (yet it has drifted up but the value isn't that critical).
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 12, 2018, 04:43:04 PM
ok    sw on 0   2.0
        sw on 10    it jumps around from -8.0  to -34
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 12, 2018, 04:59:52 PM
Quote
sw on 0   2.0
        sw on 10    it jumps around from -8.0  to -34
Not quite as symmetrical as I'd expect but at least you can get + and - so that's a good start.

The jumping around sounds like a bad contact in the pot.
Maybe the pot needs cleaning.
Sometimes moving it backward and forward a few times helps (for now) but later it will go bad again.

The main point is you can  get + and -.   You should be able to measure the voltage between V2 pin 1 and V2 pin 6 and adjust the pot to get zero output voltage.

Another thing you can check is the voltage on pin 4 of the pot to ground.  It should stay at a fixed voltage when you adjust the pot.  I expect about 40V there.
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 12, 2018, 07:22:20 PM
Oh,  another test is to measure the voltage difference between pin 3 and pin 4 of the pot for different pot settings.
If it's not symmetrical try pulling out V2 and re-checking.
If it's still not symmetrical there might be something weird going on with the pot, or perhaps leaky caps (but that would be low on the list).

Title: Re: help with oscilloscope model 34
Post by: whomeno on October 12, 2018, 09:41:30 PM
across v2  pins 1 & 6 I can take it too 0
which would be pin 4? here is a pic


(https://i.postimg.cc/t1232zxd/100-0762.jpg) (https://postimg.cc/t1232zxd)
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 12, 2018, 09:49:30 PM
Quote
across v2  pins 1 & 6 I can take it too 0
OK cool.   That means V2 and surround is probably working.

Quote
which would be pin 4? here is a pic
Pin 4 of the pot is single terminal with green wire on the left.
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 12, 2018, 09:54:09 PM
pin 3 would be below 2 right? not Above
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 12, 2018, 10:02:14 PM
ok  pin 4 to   pin above pin2  12v to 14v
pin 4 to pin below  pin2  -12 to -14
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 12, 2018, 10:35:58 PM
will be back on saturday.
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 12, 2018, 10:58:32 PM
Quote
ok  pin 4 to   pin above pin2  12v to 14v
pin 4 to pin below  pin2  -12 to -14
Those look good.

I think you measure the right voltage despite my mistyping.
I meant measure between pins *2* and 4 on the pot.

Here's the marked up pic:

(https://i.postimg.cc/06k8fdyq/vertical-position-pot.png) (https://postimg.cc/06k8fdyq)

Anyway,  is it possible to adjust the Vertical Position pot to get zero voltages between pin 6 and pin 1 of V2 ?

***** For some reason the pot is wired up with pin 1 in as the clockwise position.  Don't worry about that.
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 12, 2018, 10:59:34 PM
Quote
will be back on saturday.
OK no problem.
I think we are getting close to checking/debugging getting a green dot.
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 13, 2018, 10:38:28 AM
yes i can  adjust the Vertical Position pot to get zero voltages between pin 6 and pin 1 of V2
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 13, 2018, 05:49:09 PM
Quote
yes i can  adjust the Vertical Position pot to get zero voltages between pin 6 and pin 1 of V2
OK cool.

Do the following:
- Make sure all the tubes are in.
- Make sure the Sweep Selector (Red) is set to EXT.
- Set Vertical position so the voltage between pin 1 and pin 6 of V2 is zero
- Set Horizontal position so the voltage between pin 1 and pin 6 of V6 is zero
- Set the Intensity pot to full

Note down the positions of the Vertical position and Horizontal position pots so you
can set them back to that position quickly.

Do you see a dot or any form of green light from the screen?

Also, try wiggling the Focus control back and forth.
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 13, 2018, 06:30:41 PM
I think there is something wrong with the Vertical switch. I can't get it to zero now.
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 13, 2018, 06:34:32 PM
FYI,  my only "concern" at this point is normally the voltages on V2 and the voltage on V6 are about equal.
The Heathkit schematic shows these all at 280V.   From above, after adjusting the pots to get equal voltages, you were getting about 320V on V2 and 225V on V6.   So V2 high and V2 low and they are not equal.

Need to check if the drifted resistors values are contributing to this.

Maybe measure the voltages:
- "B+b" marked on the schematic, where R32 (1k) and R26 (1K) join
- "B+c" marked on the schematic, where R52 (27k) and R53 (27k) join.
- While you are there, measure "B+a+, at any point on the wire connecting R56, R31, R45 etc.



Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 13, 2018, 06:36:16 PM
Quote
I think there is something wrong with the Vertical switch. I can't get it to zero now.
It might be dirty.  You can clean it with electronic contact cleaner.
Sometimes you can wiggle it backward and forward a bit to get it going however it often goes bad again later.
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 13, 2018, 07:14:48 PM
where R23 (1k) and R26 (1K) join  359v
where R52 (27k) and R53 (27k) join  356v
for the life of me I can not find these resistors R56, R31, R45
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 13, 2018, 07:46:07 PM
Quote
for the life of me I can not find these resistors R56, R31, R45
Have a look at my pic from post #16.

One side of R56 (5k) is  B+b = 359V = the voltage you measure between R23 (1k) and R26 (1K).
The other side of R56 is B+a ; should be about 135V.
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 13, 2018, 07:53:44 PM
200 but it drops as time moves
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 13, 2018, 08:10:47 PM
Quote
200 but it drops as time moves
OK a but higher than I expected from the Heathkit circuit  - not a crazy value.
Same as the other voltages, B+b and B+a, not a close to the Heathkit as I hoped  - again, not crazy values.
They aren't exactly the *same* circuit so we might expect some differences.

Anyway, did you have any luck getting the Vertical Position pot to work?
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 13, 2018, 08:23:58 PM
not yet I will let you know when I got it working
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 13, 2018, 08:29:54 PM
Quote
not yet I will let you know when I got it working
It's best if you can get it working.

If you are really desperate and want to continue there is a trick to force the balance of the tubes.   You simply short the two anodes of V2 together and short the two anodes of V6 together.   From that point you can debug the CRT part.
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 13, 2018, 09:35:21 PM
I got it to zero but still no dot
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 14, 2018, 12:22:41 AM
c33A  =  425v
C33B  =  373v
C33C  =  348v
C33D  =  160v
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 14, 2018, 03:34:47 AM
Quote
c33A  =  425v
C33B  =  373v
C33C  =  348v
C33D  =  160v
Those voltage look better.

We need to measure the resistors around the tube.
One could be open circuit.
However you will need to discharge some caps first.

*** Do not touch any of the parts or wires around
      this whole area of the circuit.
      The voltages in this part of the circuit are 1000V to 1500V.
      They will zap you and your meter!

- Power off the unit
- Discharge C21, C30, C31, C32
- Measure the resistances R60, R62, R63, R67.
  You might have to wait a 30 secs or more for some of the measurements to settle
  (because we are measuring in circuit).
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 14, 2018, 12:38:37 PM
ok,  R59  1M = 888
R60 1M =   1.025
R62   560K = 606
R63   220K = 348
Is R64 the switch ?
I can not find a R67
Title: Re: help with oscilloscope model 34
Post by: amptramp on October 14, 2018, 07:15:51 PM
With equipment of this age, the high voltage capacitors, C30, C31 and C32 often leak to the extent that the voltage goes below the amount necessary to provide enough voltage for anything to be seen.  Discharge them and pull them out of circuit and measure their resistance.  It should be above 30 megohms and even that is suspect.
Title: Re: help with oscilloscope model 34
Post by: Slowpoke101 on October 14, 2018, 07:36:25 PM
Is R64 the switch ?
I can not find a R67

I think Rob meant R57 which should be 3M3
R64 (spot shape) appears to be (referring to the schematic) a 2M pot as is R58 (focus).
R64 may have been replaced or substituted by a switch (odd but possible).
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 14, 2018, 07:44:51 PM
Quote
ok,  R59  1M = 888
R60 1M =   1.025
R62   560K = 606
R63   220K = 348
Is R64 the switch ?
I can not find a R67
Yes, R64 is the pot.

I think the resistor numbers stop at R64 so no R67.   That's my typo I meant R57.

Obviously some of the resistors have drifted, especially R63.

*** Remember to be careful around this area of the circuit and don't touch anything
     while you are measuring.

The next step is to check if there's any CRT beam current.
- Turn on the unit and wait about 30 secs to 1 minute
- Turn the Intensity Pot to maximum
- Measure the voltages across R60, R62, R63
- Turn the Intensity Pot to minimum
- Measure the voltages across R60, R62, R63

After that you probably need to make a High Voltage Probe.
In order to determine the meter input impedance do the following:
- Set the multimeter to DC voltage
- Measure the voltage on say a 9V battery.
- Put a 10M resistorsin series with the +ve lead of the meter.
- Remeasure the battery voltage using the free end of the 10M resistor.
  You should expect somewhere between 1V and 4.5V depending on your meter impedance.

Quote
I think Rob meant R57 which should be 3M3
Yes!
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 14, 2018, 08:11:23 PM
what voltage should I see across the resistors?
My meter only go up to 600v
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 14, 2018, 08:17:24 PM
battery 9.56
with 10m =.87
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 14, 2018, 09:10:20 PM
Quote
what voltage should I see across the resistors?
My meter only go up to 600v
Hold off on doing that measurement.
We need to setup a good/safe way to do it.


Title: Re: help with oscilloscope model 34
Post by: whomeno on October 14, 2018, 11:48:13 PM
OK I will wait till you have a good plan
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 15, 2018, 08:49:51 PM
Quote
battery 9.56 with 10m =.87
FYI, your UTL33T multimeter input impedance is 1M ohm.
Most meters are 10M but the cheaper ones are often 1M.

Quote
OK I will wait till you have a good plan

Here's the problem:

I'm fairly sure there is a problem with the high voltage circuits around the CRT.  Exactly what I don't know.   In order to zoom-in on the problem we need to make measurements.

One way is to make voltage measurements but that means measuring high voltages.  We also have to be careful the meter doesn't load the circuit and give is a false reading.

Another way is to remove enough parts so all the parts around the high-voltage circuits can be measured individually.   That includes measure the pots and making sure the pot wipers are actually connecting properly to the resistive track of the pot.  Any part that is faulty you replace.    After replacing the parts you power it up and hope it works.    If it doesn't you have little option but to fall back on the measuring the high voltages.

I've put the Bell&Howell 34 and Heathkit IO-12 HV circuits side-by-side in order to compare the voltages.

(https://i.postimg.cc/8sxz7j2N/CRT-voltages-sch.png) (https://postimg.cc/8sxz7j2N)

The beam current measurement I mentioned before usually only requires the measurement of a < 100V voltage across a resistors.  However, that assumes it is working.  If there is a fault then the measurement might get up to 1500V.

Also there's one thing that looks weird to me about that circuit.  The cathode (pin 3 of the CRT) connects to the HV via a 1M resistor (R60).  I'd expect the beam current to be around 100 to 500uA however a 1M resistor will cause 100 to 500V drop.  Normally that resistor is smaller and the voltage drop is smaller.  I can't see how the beam current passes current through R60.  But then I look at the grid G1 (pin2 of the CRT).  On the Heathkit circuit there's (1200 - 1180) = 20V drop across a 100k so I = 200uA which is in the order of the beam current I expect.  However, I don't know why such a high current is passing through a grid.     Just to top it off, on Bell & Howell, the equivalent grid resistor is 560k.  At 200uA that's going to have about 112V drop across it - which is more than normal.  I obviously don't understand something about that particular CRT tube.

Title: Re: help with oscilloscope model 34
Post by: whomeno on October 15, 2018, 09:47:21 PM
I do have the devry 1s14 which dose go to 1500 volt. but there  is a pot on the back to calibrate it. How would I do that?
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 15, 2018, 10:13:19 PM
Quote
I do have the devry 1s14 which dose go to 1500 volt. but there  is a pot on the back to calibrate it. How would I do that?
I already sent a reply to your PM.
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 15, 2018, 11:21:46 PM
I got pm.
calibrated meter
5Up1 voltages
pin1 = 0
pin2 = 0
pin 3 =0
pin4 = 0
pin5 = n/c
pin6 =250
pin7 = 240
pin8 = 240
pin 9 = 190
pin 10 = 180
pin 11 = n/C
pin12 = 0
how do I read neg volts?
can not get a reading across resistors
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 15, 2018, 11:29:25 PM
ok vm has dc- but still reads o for neg readings
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 15, 2018, 11:45:58 PM
Quote
ok vm has dc- but still reads o for neg readings

***** Hold-off on using that meter any further *****

I found a schematic on the web.  It looks like the negative terminal is grounded!

When you connected it to another circuit the -ve lead on the meter might short the supply through mains earth.

Also, and more of a problem, when you connect the -ve lead to a dangerous voltage it might make the case of the meter the same dangerous voltage.


***** Also don't go using this meter to measure any mains voltages *****
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 15, 2018, 11:47:34 PM
ok
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 15, 2018, 11:49:31 PM
***** Also don't go using this meter to measure any mains voltages *****
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 15, 2018, 11:52:26 PM
ok no more meter.
Title: Re: help with oscilloscope model 34
Post by: Slowpoke101 on October 16, 2018, 01:44:04 AM
Not wanting to cause any confusion but I find the measured resistance of R63 to be very high even with age drift.
I suggest making sure that no power is applied and all caps have discharged, lift one leg of R63 and measure directly across it. Remember to resolder the resistor back in position when finished.

Word of warning - if R63 is open circuit, C30 may not have discharged. Wait at least 10 minutes after power off and then carefully measure for voltage across C30. Put a 10M resistor in series with the multimeter's positive test lead to help protect the meter just in case C30 is fully charged.
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 16, 2018, 01:58:55 AM
Quote
Not wanting to cause any confusion but I find the measured resistance of R63 to be very high even with age drift.
No confusion.   It's bad for sure.   There may be more.

Quote
Word of warning - if R63 is open circuit, C30 may not have discharged. Wait at least 10 minutes after power off and then carefully measure for voltage across C30. Put a 10M resistor in series with the multimeter's positive test lead to help protect the meter just in case C30 is fully charged.
I think whomeno needs to build a simple HV probe.   Simple in the sense of handling 2kV and not 20kV to 40kV like some.

I haven't suggested 10M in series with the meter because common 0.25W to 0.5W resistors, the ones about 6.5mm long, are only rated for 250V.   For 1500V we really need at least 6 resistors in series covered with a few layers of insulation/heatshrink.

The voltage rating issue also brings up problems with replacing the resistors.  You really need to replace the resistors using high voltage rated ones not the common garden electonics store stuff.
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 16, 2018, 04:07:39 AM
Here's a simple 1.5kV Probe which will *just* do the job.
The circuit has a 60M ohm input impedance which shouldn't load the circuit much.

(https://i.postimg.cc/kBxFNYWY/1-5kv-probe-with-annotations.png) (https://postimg.cc/kBxFNYWY)

The earth clip connects to the circuit's 0V/Earth.  Nowhere else.  You cannot measure across resistors.

The probe touches the point you want to measure.

The resistors are through-hole types and need to be at least rated to at least 250V.  Those miniature resistors with body lengths around 3.5mm are too small and won't be 250V.  The ones with body lengths longer than  6.5mm are usually 250V.  Higher voltage resistors are of course much better is you want to buy them.

Connecting the resistors like this will do, 
https://forum.makehackvoid.com/t/1000-1-hv-probe/230

Here's another way to do the resistors but it needs to the tube to make it stiff and not put mechanical stress on the solder joints,
https://www.instructables.com/id/DIY-HIGH-VOLTAGE-MULTIMETER-PROBE/


Title: Re: help with oscilloscope model 34
Post by: whomeno on October 16, 2018, 07:50:21 AM
Rob,
how many 10m ohm would I need to be able to measure the mains. I am looking at building an amp in the future .If I am going to build one I want to do it right. After the heat shrink, I could put it in a pvc pipe and seal it
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 16, 2018, 11:05:41 AM
1.5kv probe done.


(https://i.postimg.cc/Hc4tGsZM/20181016-110305.jpg) (https://postimg.cc/Hc4tGsZM)
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 16, 2018, 05:14:54 PM
Quote
how many 10m ohm would I need to be able to measure the mains. I am looking at building an amp in the future .If I am going to build one I want to do it right. After the heat shrink, I could put it in a pvc pipe and seal it
It's got more to do with the construction.   Technically, these days you probably shouldn't measure mains inside equipment unless the meter *and leads* have at least at Cat II rating and a suitable voltage rating.  For fuseboxes etc you need Cat III or above.   The meters before about 1998/1999 don't tend to have markings, not even Flukes, and you need to decipher the manual.     A lot of cheaper meters and probes don't comply to the Cat ratings.

https://content.fluke.com/promotions/promo-dmm/0518-dmm-campaign/dmm/fluke_dmm-chfr/files/safetyguidelines.pdf

So you should only connect the 1.5kV probe to the non mains inside of equipment.
For testing HV inside of equipment, if the earth clip comes off the ground the 6x10M's will limit current to a safe level.   For example, Current I = 1.5kV /(6*10MEG) = 25uA.  This is would even pass the leakage test for medical equipment.
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 16, 2018, 05:25:15 PM
ok, so what do I need to check now?
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 16, 2018, 05:27:05 PM
Quote
1.5kv probe done.
Quote
ok, so what do I need to check now?

Looks pretty good.

The probe part looks a bit long you might want to slip some heatshrink over the end so only 1/2" (12mm), or less, of the tip is expose.  That will prevent accidental shorts on other stuff.

The thing to do now is to test the probe on low voltage then gradually move up.  If you find a problem don't continue with the higher voltages.

- Measure a 9V battery without the probe, then measure the 9V battery with the probe.   You expect 9/1000 = 9mV.
- Measure a 100V supply without the probe, then measure the 100V supply with the probe.   You expect 100/1000 = 100mV.
- Measure a 300V supply without the probe, then measure the 300V supply with the probe.   You expect 300/1000 = 300mV.
- Measure a 500V supply without the probe, then measure the 500V supply with the probe.   You expect 500/1000 = 500mV.

These don't have to be exact voltages the main point is to get some coverage across the range.  Your meter provides the reference.   For the higher voltages try to measure the actual power supply voltages not things like tube anodes.  The reason is, the tube anodes have high value resistors and your meter will give you a false low reading because its 1M input impedance loads the circuit.

Record the points.  If you can, record the value of the resistance feeding the supply rail. You will find the probe might be a little off (maybe +/-5% to10%) because of the resistor tolerances and possibly because your existing meter is loading the circuit.

There's a leakage test but I have to see what your meter can do.
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 16, 2018, 05:35:54 PM
Actually there are more basic tests to do first:

Using the ohms scale on your meter:
- Measure the resistance between the DMM- lead and the Earth clip.  Should be less than 0.5ohm.
- Measure the resistance between the DMM- lead and the DMM + lead.  Should be 63.7k +/- 5%.
- Measure the resistance between the Probe TIP and each of the other leads.  Wait about 30 seconds between each measurement.  It should be about 60M ohm +/- 10%.  However your meter might not provide a measurement.    If it shows overload, and you have made good contact, then it is at least 20M.
A leakage test will help measure this.
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 16, 2018, 05:37:33 PM
battery 9.55v
probe .008

203 volt
probe 0.19 on 20 on meter

346 Volt
probe 0.2 set on 200 on meter

428volt
0.3 set on 200 on meter
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 16, 2018, 05:44:21 PM
ok
gr and earth =.53 set on 20 on meter
DMM- lead and the DMM + lead. = 62.9
dimm- and tip =61.7
dimm earth and tip = 61.7
dimm + and tip =61.7
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 16, 2018, 05:46:52 PM
Quote
DMM- lead and the DMM + lead. = 62.9
Is that kilo ohms?

Quote
dimm- and tip =61.7
dimm earth and tip = 61.7
dimm + and tip =61.7
Is that Mega ohms?
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 16, 2018, 05:49:27 PM
Quote
battery 9.55v
probe .008

203 volt
probe 0.19 on 20 on meter

346 Volt
probe 0.2 set on 200 on meter

428volt
0.3 set on 200 on meter
Ah, your meter is manually ranged.
For accurate results the meter needs to be set on the 2V range when used with the probe.
With the probe, a reading of 1.2V on the meter now means 1.2kV as the probe divides the voltage by 1000.
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 16, 2018, 05:52:13 PM
meter set on 200m   61.7 mohms
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 16, 2018, 06:00:22 PM
9.55v
probe = .008

202volt
probe = .197

360 Volt
probe =.361

415 volt
probe =.403
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 16, 2018, 06:20:33 PM
Those are much better.

I calculated the measurement errors below so they are within say +/-3%.
If the reference meter is loading the supply at all then the true error could
be a bit more in the negative direction.

Meter UTL33T manually set to 2V
Ref Meter   1.5kV probe   Error %
202V           197V             -2.48%
360V         361V           0.28%
415V            403V           -2.89%

OK we need to do a leakage test.   
I'll draw-up the set-up.
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 16, 2018, 06:22:10 PM
For convenience I've linked your UTL UTL33T meter manual:
https://inspectusa.com/uei/UTL33T-PS.pdf
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 16, 2018, 06:33:35 PM
is there a little better meter out there that will not kill my wallet?
This one was 19.99 years ago
What would be a good choice under 50.00
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 16, 2018, 06:51:57 PM
Here's the leakage test (click to enlarge),

(https://i.postimg.cc/DJxjHdNH/leakage-test.png) (https://postimg.cc/DJxjHdNH)
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 16, 2018, 07:05:01 PM
Quote
is there a little better meter out there that will not kill my wallet?
This one was 19.99 years ago
What would be a good choice under 50.00
I'm scared to recommend any $50.00 meters as they vary enormously
and to be honest many are probably of poorer quality than what you have.
There's a stack of meter shootouts on youtube's EEVblog channel.
Unfortunately they are a bit dated not. The general conclusion is the $50 meters
aren't great and you need to spend $100.

A lot of $50 meters don't have gold switch contacts.  Also the switch and meter contacts fail quite often.
I have seen this on some of the cheaper meters at work.

Beyond the quality issue is the features you want from a meter.  This will further limit the choices.

I have a $30 meter which I bought for $10 20 years ago.  I use it for kamikaze jobs.
The switch contacts are all gold and it has survived this long. 
The supplied leads are totally crap and the type of leads aren't a modern style.
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 16, 2018, 07:13:55 PM
if i set meter to 2v I get 1 error
set meter to 20
probe + 1.64
probe-  1.62
probe earth= 1.61
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 16, 2018, 07:37:52 PM
Quote
if i set meter to 2v I get 1 error
set meter to 20
probe + 1.64
probe-  1.62
probe earth= 1.61
I think you did the test wrong.
For the leakage test only you need to set the meter to 2mA DC.
When you finish the test set the meter back to volts.
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 16, 2018, 07:46:53 PM
meter dose not have a 2 ma - 600v 200v 20v 2v 200m
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 16, 2018, 07:53:26 PM
i'm sorry i found it.
getting 0 on all
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 16, 2018, 07:57:10 PM
I am using c33a as 400volt source
dimm - to ground
each lead of probe to dimm +
1 at a time
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 16, 2018, 08:00:18 PM
Quote
i'm sorry i found it.
getting 0 on all
Not good.   
I think the fuse in your meter is blown.

You can check the fuse as follows using a 9V battery:

- Set meter to 2mA DC

- Connect up a circuit like this (a big circle)

        +9V  ->  10 k ohm resistor ->  Meter + terminals
and    0V    ->   Meter -  terminals   

- Take the measurement.
   If it is 0.9mA then the fuse is OK. 
   If it is 0 then the fuse is blown.

- Set the meter to 2V DC.
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 16, 2018, 08:35:04 PM
fuse is shot.
will need to find another one.
will let you know when back up and running
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 16, 2018, 08:39:13 PM
Quote
fuse is shot.
will need to find another one.
will let you know when back up and running
No worries.
What can happen is if you are measuring a voltage and spin the meter switch over any of those mA or A ranges it will create a near short across the meter leads and normally blow the fuse.   You should watch out for this because it can create a hazard (and blow-up the circuit).
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 16, 2018, 08:41:48 PM
ok will do need to order some in.
nobody around here has them
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 17, 2018, 01:29:11 AM
Quote
if i set meter to 2v I get 1 error
set meter to 20
probe + 1.64
probe-  1.62
probe earth= 1.61
Your meter has some funky behaviour.

The previous battery +10M test in Post Reply #88 shows the multimeter input impedance is 1MEG on the 2V range.  For 1M input impedance I would expect the result of this "incorrect" test to produce 6.7V,  which is expected to overload the 2V range (ie. the  "1" on the DMM display).

However for the 20V range we don't get 6.7V we get 1.6V.  That implies the input impedance of your meter on the 20V ranges is only 244k ohm.   So it has dropped by a factor of 4.   An input impedance of 244k ohm is quite low for a DMM.  Notice also if you were on 20V range and saw a 1.6V reading you would think you could step down to the 2V range but when you did it you would get an overload.
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 17, 2018, 09:34:01 AM
leak down test
probe + lead = .006
probe - Lead =.006
probe earth lead =.006
meter set on 2ma
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 17, 2018, 09:45:52 AM
redid the 10m ohm test
on 20v it gives a 0.86
on 2 v it gives a 0.867
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 17, 2018, 05:33:32 PM
Quote
leak down test
probe + lead = .006
probe - Lead =.006
probe earth lead =.006
meter set on 2ma
OK, all those look good.
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 17, 2018, 05:37:38 PM
Quote
redid the 10m ohm test
on 20v it gives a 0.86
on 2 v it gives a 0.867
Hmmm.  From those measurements the impedance works out to be 1M ohm on both 2V and 20V.  That's more of a normal result.

Not sure what happened in the previous test.    It worries me when I see weird results.
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 17, 2018, 06:22:43 PM
kewl, so what is the next steps
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 17, 2018, 07:09:47 PM
I will replace resisters and capacitors if need be. Would like to know if the 5Up1 is ok.
On the resistors that is not marked with a wattage ,what size would I use?
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 17, 2018, 07:45:27 PM
Quote
kewl, so what is the next steps
The next steps you have to be freaking careful as you need to measure dangerous voltages!!!
You have to make sure all the connections are correct, the meter is set correctly
and you are probing the right points, even which side of the resistors,  *before you start*. 
Plan it all out up front.   

Don't measure anything yet.  I'll mark-up the schematic.

Title: Re: help with oscilloscope model 34
Post by: whomeno on October 17, 2018, 07:50:00 PM
ok I replaced R63 220k measures 260 now instead of  360
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 17, 2018, 08:30:32 PM
Quote
I will replace resisters and capacitors if need be. Would like to know if the 5Up1 is ok.
On the resistors that is not marked with a wattage ,what size would I use?
These days the best resistors for that part of the of circuit probably Flame Proof Metal Oxides.
I'll have to check you pics for the wattage.   
The caps are special items. 

Quote
ok I replaced R63 220k measures 260 now instead of  360
I'm not fond of using standard resistors in HV circuits.   The standard resistors only handle 250V.
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 17, 2018, 08:38:51 PM
i had some old stock here. it is the same type of resistor. that is why it read 260 instead of 220.
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 17, 2018, 08:46:12 PM
where would be the best place to get the Flame Proof Metal Oxides?
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 17, 2018, 09:41:16 PM
I found them on digikey
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 17, 2018, 10:30:14 PM
Quote
I found them on digikey
Bigger suppliers are more likely to keep them.

You have to get the correct power and voltage.
I don't know what's in the unit as it's not marked on the schematic.

Most old style carbon composites, the ones that are in the unit now, were 700V to 1000V.   At least that's what was quoted in the day.    Modern carbon composites are somewhat less for the same size package.

The voltage you want is working voltage (not overload or dielectric withstand).  Without any additional info a 1000V rating is safest.

"Limiting Element Voltage" comes up on the datasheet a lot.


Title: Re: help with oscilloscope model 34
Post by: whomeno on October 17, 2018, 11:07:04 PM
1000v what would that be in watts 1w 2 w?
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 17, 2018, 11:18:24 PM
Quote
1000v what would that be in watts 1w 2 w?

They are completely different things.

No offense,  but I don't think you aren't up to doing this project.
You are going to get hurt. 
Stop!
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 17, 2018, 11:24:33 PM
I just don't under stand .
you said use 1000 volt resistor
Resister are rated in watts not volts
on the schmatic it has which resisters need to be 1 watt -2watt and so on
if they are not marked as 1-2-3 watt what would the be?
smaller then 1 watt?
I ask question before doing any thing if I don't under stand.
I would love to finish this project. You have taught me a lot over the past days.
Title: Re: help with oscilloscope model 34
Post by: bluebunny on October 18, 2018, 02:30:36 AM
I just don't under stand .
you said use 1000 volt resistor
Resister are rated in watts not volts

If you look at the datasheet for a resistor, you will see that it has a maximum voltage rating too.
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 18, 2018, 02:31:40 AM
I found a place that sells the same resistors used in the build.
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 18, 2018, 02:32:40 AM
thanks bluebunny
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 18, 2018, 02:34:05 AM
I hope I didn't make Rob mad at me. sure hope he helps finish this.
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 18, 2018, 11:39:26 AM
measure votage across 60 62 63
intensity max
R60=7.68
R62 = .010
R63 = -2.161

intensity min
R60 = 5.914
R62 = .013
R63 = -1.57
done with new meter
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 18, 2018, 04:33:34 PM
new meter is auto range and 10m input impedance

meter input impedance
battery = 9.60
with 10m resistor =5.01

Probe check
battery 9.60
with probe =.009

151v w probe= .154
234v w probe =.241
352.6 v w probe = .360
427.4 w probe = .436

resistance of probe
DMM- to earth =.4
dimm- to dimm + =OL
probe tip to earth =OL
probe tip to dimm=OL
probe tip to dimm+ =OL

leak down test meter set on auto dc volts
probe +  = 59
probe-  =  59
probe earth = 59



(https://i.postimg.cc/cvH7DxcC/20181018-165338.jpg) (https://postimg.cc/cvH7DxcC)
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 18, 2018, 05:45:27 PM
Quote
I hope I didn't make Rob mad at me. sure hope he helps finish this.

I'm not mad.  I'm just concerned.   I've done this stuff a long time and I can see you have limited experience.  That's fair enough everyone is in the same position at some point.  This job is risky you can get electrocuted.   If your mind is thinking about how to set the meter you aren't thinking five steps ahead to avoid the dangers.

Imagine going on an climb to Mt Everest with limited experience.   It doesn't matter how experienced your guide is, you are at extreme risk.   Your guide can tell you stuff but  if you make a mistake tying one of the knots you will be in trouble.   The guide's not only thinking about the knots (which he can do easily) he's thinking about checking the knots and thinking many steps ahead, making choices so he doesn't get into trouble.   If you have limited experience you might not even be aware of the danger at all.   This is how you get in trouble.

Here's an example where you are close to danger. It's in the area of the power supply where
you are making measurements.   It's very easy to slip or make a mistake.

Click to enlarge:
(https://i.postimg.cc/5HNWxtrH/mains-cables.jpg) (https://postimg.cc/5HNWxtrH)

I might add the unit is not Earthed. It uses a two-wire mains cable.

Also the mains inlet is just knotted and can push-in and get amongst the 1kV stuff.
That old mains cable is not rated for 1kV.
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 18, 2018, 06:20:54 PM
I do understand your concerns. I know this can kill me that is why I have been taking my time and learning from you. Like i told you in messenger I have worked with 3 phase 440 and 410. But you have helped me through this so far and i hope we can continue or journey.
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 18, 2018, 06:28:06 PM
Quote
leak down test meter set on auto dc volts
probe +  = 59
probe-  =  59
probe earth = 59

With the new meter the leakage test has to be done differently.

To measure current on your old meter you have to:
- Set the current range
- Use meter terminals  "COM" and "V".  ie. same meter terminals as the voltage measurements.

To measure current on the new meter you have
- Set the meter to current range
-  Use the terminals COM and mA/uA.

For the new meter there is essentially a short between COM and the 10A terminal and also a short between COM and the mA/uA terminal.

A good practice is to move the meter lead from mA/uA to V as soon as you are finished doing a current measurement.   If you leave the meter lead in the mA/uA socket and then later go to measure a voltage the meter will short out the circuit you are measuring and create a big bang.    Accidentally leaving the meter leads plugged into 10A then doing a mains measurement is a very hazardous situation because you are shorting out the mains supply with the meter.
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 18, 2018, 06:37:31 PM
Set the meter to current range----That would be the ma  on the dial?
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 18, 2018, 06:39:28 PM
Quote
new meter is auto range and 10m input impedance

meter input impedance
battery = 9.60
with 10m resistor =5.01
OK and that test confirms the meter is 10M

Quote
Probe check
battery 9.60
with probe =.009

151v w probe= .154
234v w probe =.241
352.6 v w probe = .360
427.4 w probe = .436
Ok those voltages look good.

FYI:  The R8 in the 1.5kV Probe was actually chosen for your old meter with 1M input impedances.
With the new 10M input impedance meter a value of R8=1M  should make the 1.5kV Probe should measure +5% higher.  However, because the parts have tolerances it is actually only 3% high; on the old meter it was 2% low.  Anyway, the accuracy is fine and there's no need to change R8.

Quote
resistance of probe
DMM- to earth =.4
dimm- to dimm + =OL
probe tip to earth =OL
probe tip to dimm=OL
probe tip to dimm+ =OL
The new meter only goes upto 20M ohm and we are expecting 60M ohm.   The old meter can go to 200M ohm, so it can do something the new meter can't.

Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 18, 2018, 06:42:11 PM
Quote
Set the meter to current range----That would be the ma  on the dial?
Yes.   Just set it to the 2mA range.

FYI: I think your new meter can do 200uA which will give a better measurement. 
You can try both.
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 18, 2018, 06:55:08 PM
on ma ===0
on  UA all three are 6.8
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 18, 2018, 06:59:35 PM
Have to go make supper. My wife has Brain cancer so I do all the work around the house. Be back in An hour.
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 18, 2018, 07:06:23 PM
Quote
on ma ===0
on  UA all three are 6.8

It's odd the mA range is zero.
I think it might be on the 200mA range not 2mA.
I'll need to find a manual for the meter.

The uA measurement looks good. 
6.8ua = 0.0068mA 
which agrees with 0.007mA pass requirement (which is actually 0.0067mA rounded up to 0.007mA)

Meter issues aside, the leakage test passes.
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 18, 2018, 07:07:00 PM
Quote
Have to go make supper. My wife has Brain cancer so I do all the work around the house. Be back in An hour.
No problems.
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 18, 2018, 07:14:41 PM
Quote
It's odd the mA range is zero.
I think it might be on the 200mA range not 2mA.
I'll need to find a manual for the meter.
I found this info on your meter:

"DC Current Range: 6000μA/600μA /60mA/600mA /10A"
6000uA = 6mA.

When you select the mA current range does the meter display show "AC" ? 
Some meters default to AC and you have to press a button to get DC.
Be aware some meters have a third option of AC + DC; you only use this in special circumstances.
(from what I can see yours doesn't have this.)
------------------------------
More info:

From,
https://www.amazon.com/gp/product/B078JDL61X/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

Click, "See more product details" at the bottom of the description text.

Then you will see,

DC/AC Current Measurement
Step 1. Insert the black test lead into the "COM" socket, insert the red test lead into the "mA / uA" jack, or insert the red test lead into "10A" (max. 10A)
Step 2. Press "SELECT" botton to switch between AC and DC current
Step 3. Turn the range switch to the corresponding "DC/AC" position, connect the device into the circuit to test.
Step 4. The current value of the measured current and the polarity of the red test point will also be displayed on the screen at the same time.


So it does have an AC/DC button.  I just don't know if it starts up in AC or DC mode.
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 18, 2018, 07:54:44 PM
yes it defaults to dc. I tried the range button all it dose is move the point over form 0.000 to 00.00 and to 000.0
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 18, 2018, 09:05:02 PM
Quote
yes it defaults to dc. I tried the range button all it dose is move the point over form 0.000 to 00.00 and to 000.0
It's probably worth getting to the bottom of this.  It's a distraction from the main job but it will come back to get you one day.  The meter could even have a problem.

- Connect this up:
   9V battery --->   100k resistor  ---> Red Meter lead inserted in the meter mA/uA socket
   0V battery --->  Black meter lead inserted into the meter COM socket

  We expect approximately I = 9V / 100k = 90uA.

- Meter set switch to uA.   Read current.  Should be about 90uA.
- Set meter switch mA.   Set range to 6mA ie. "0.000".  Read current.  Should read 0.090 mA.
- Press the range switch to set range to 60mA ie. "00.00". Read current.  Should read 00.00mA,
  you might see 00.01mA; both are OK.
- Plug red meter lead back into V terminal.
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 18, 2018, 09:15:21 PM
ok in UA mode will only give me 000.0 reading was 95.4
in MA mode 00.00 = .08 MA other mode is 000.0
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 18, 2018, 09:21:21 PM
slowpoke had me test the transformer  here are the results
V8 pin 5 to gr =1.76
v8 pin 4 to gr = open
V6 pin 1 to gr = .01
V6 pin 6 to gr =.01
V7 pin 1 to gr = open
V7 pin 6 to gr = open
shot transformer right?
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 18, 2018, 09:24:40 PM
 resistance between V8 pin 4 and pin 5 = open
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 18, 2018, 09:34:31 PM
Quote
slowpoke had me test the transformer  here are the results
Worth doing.

Quote
V7 pin 1 to gr = open
V7 pin 6 to gr = open
shot transformer right?
Something is wrong with the measurements.  Are you on a high ohms scale?
If these windings were open I wouldn't expect to get 400V and all the DC voltages we saw previously.

Also, from what I can see from your measurements across R60, R62, R63 (Reply #150) you are getting some current through the 1200V/1400V rail.  The intensity control is also changing the current.


Title: Re: help with oscilloscope model 34
Post by: whomeno on October 18, 2018, 09:40:28 PM
I'm so glad you said that. the meter was set on 2k (old meter). slowpoke was not sure on his findings. he just said"Hopefully Rob will see something I missed and the transformer is OK. Just reassure him that all tests were done without power being applied and with the plug removed."
ok so my hopes are up again
Thanks
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 18, 2018, 09:43:04 PM
If you are confident about taking a measurement, the voltage across R57 would be a good indicator.
- Turn off the unit.
- Wait about 1min
- Set the meter to 1000V DC scale.
- Make sure the meter leads are in the COM and V terminals
- Wire the meter to R57 (the side that goes to the Focus pot) and ground
- Power up the unit and take the measurement.
   (- You expect about 550V)
- Turn off the unit 
- Wait about 1min

Be careful!

Title: Re: help with oscilloscope model 34
Post by: whomeno on October 18, 2018, 10:04:53 PM
ok done
with meter set  dc auto 1.034
with meter set to 0.000=1.034
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 18, 2018, 10:27:53 PM
Quote
ok done
with meter set  dc auto 1.034
with meter set to 0.000=1.034
Well that's way off.

I've got an idea.
- Turn the unit off the unit
- Remove the power plug from the mains
- Wait about 1/2 hr.
- Clip a wire to the ground
- With the other end of the wire, short out caps C30, C31, C30 again then C32
  for about 10 seconds.
- Remove V8
- Get a 9V battery.
- Connect the negative terminal of the battery to the chassis using a clip.
- Connect the positive terminal of the battery to the point where C30, R63, V8 pins 1 & 9 meet.
- Set your multimeter to DC voltage auto.
- Measure the following.

Click to Enlarge:
(https://i.postimg.cc/B8SRJJgw/HV-test-with-9-V-battery.png) (https://postimg.cc/B8SRJJgw)

All 8 voltages marked on the schematic.
For the measurements set the Focus pot and the intensity pot to the mid positions.
For VCRT4 measure with Focus at the mid position, when Focus on Max and when Focus on Min
For V60 measure with Intensity at the mid position, when Intensity on Max and when Intensity on Min

***** Do not power up unit in this state!!! *****

Those should be a good start.

Remove the 9V  battery when finished.

Title: Re: help with oscilloscope model 34
Post by: whomeno on October 18, 2018, 10:39:15 PM
there is nothing connected to v8 pin1
just looking not hooking anything up  on the strip  C30 R63 and V8 pin 9 connect
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 18, 2018, 10:43:33 PM
I just looked at the schematic. and v8 pin 1 should also go to the strip,right?
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 18, 2018, 10:48:11 PM
Quote
I just looked at the schematic. and v8 pin 1 should also go to the strip,right?
I think it's OK to connect only pin 9.
The tube internally connects pin 1 and pin 9.
The heathkit schematic only connects pin 9.
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 18, 2018, 10:49:41 PM
ok
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 18, 2018, 10:55:31 PM
I've added the test pic to the previous post.
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 18, 2018, 11:16:04 PM
V63  = 9.58
V61 = 8.78
V62 = 8.30
V60  mid  = 7.58
V60  min  =7.34
V60  Max  =8.0
V59 =8.05
V58  = 6.35
V57  =3.633
VCRT4 mid =5.126
VCRT4  Min  =3.630
VCRT4  Max  =6.35
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 19, 2018, 12:30:37 AM
Sorry for the delay.  Took me longer than expected to process the results.

What I've done is calculated the expected voltage in each case assuming a 10M ohm meter is loading that point.

Here's the results:  (+ = pot max, m = pot mid, - = pot min)


Measured vs Calculated Voltages         

R63=260k         
Other resistors assumed to be exact values         
         
Measurement   Vmeas_set1   Vcalc_set1   Vmeas_set1/Vcalc_set1
V61                   8.78                    9.002           0.98
V62                     8.3                    8.535           0.97
V60+                     8                    8.202           0.98
V60m             7.58            7.747           0.98
V60-                     7.34            7.320           1.00
V59                     8.05            8.006           1.01
V58                     6.35            6.352           1.00
VCRT4+             6.35            6.352            1.00
VCRT4m             5.126            4.995            1.03
VCRT4-             3.63            3.809            0.95
V57                     3.644            3.809           0.96


From a percentage error point of view the results look pretty close.
There's no obvious issues.

From a suspicion point view there's a trend of low values around points V61, V62.

The next step?   It's weird the voltage divider is OK and we are getting currents in the CRT
but your R57 measurement was way off.

Title: Re: help with oscilloscope model 34
Post by: thermionix on October 19, 2018, 12:44:52 AM
I haven't read through the whole thread, but it would be pretty sucky to go through all this trouble and find out the CRT is dead.  Do you at least see the heater lighting up?  Assuming it's not obscured by the cathode, socket, yoke or something.
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 19, 2018, 12:54:10 AM
From the part values you sent me this one looks a but suspicious,
Quote
R62 560K=185 METER SET ON 2M

Now the measurement was done in circuit and the surround parts could upset the measurement.
The paths in the circuit that would effect it are:  C32 and pin 2 of the CRT.

It could be you didn't wait long enough to take the measurement.  When you have caps in the circuit, especially with high impedances, it can take some time to settle.

Another good practice for measuring in-circuit resistances it to take two measurements.  One with the probe in one direction and one with the probe in the other.   You have to wait for the measurement to settle in each case.

Now, even if C32 had a problem it would not cause the voltage on R57 to be low.

Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 19, 2018, 12:57:24 AM
Quote
I haven't read through the whole thread, but it would be pretty sucky to go through all this trouble and find out the CRT is dead.  Do you at least see the heater lighting up?  Assuming it's not obscured by the cathode, socket, yoke or something.

I think he mentioned it was lighting up very early in the thread.  Maybe even in his other thread where be bought the equipment. see post #3 and post# 10
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 19, 2018, 01:00:32 AM
R62 560k = 927
R60 1m  = 1.023
R63  220k =325.4
R57 3.3m = 1.766
R59  1m = .887
C30 .1uf 1600v=19.16
C31 .1uf 1600v=OL
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 19, 2018, 01:02:27 AM
yes the crt is lighting up at the rear by the plug.
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 19, 2018, 01:04:51 AM
the last measurements are ohms
do you want me to put it back together and take live voltage with the probe?
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 19, 2018, 01:06:14 AM
this one was done with old meter "R62 560K=185 METER SET ON 2M"
The last set was with new meter
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 19, 2018, 01:08:14 AM
The ones i sent by messanger was resister values. done with old meter.
Just got new meter today. glad i got it
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 19, 2018, 01:11:10 AM
Quote
the last measurements are ohms
I'm not sure which ones are in ohms as some seem like they are in K or M

Quote
R62 560k = 927                 k?
R60 1m  = 1.023                         M?
R63  220k =325.4                        k?
R57 3.3m = 1.766                        M?
R59  1m = .887                           M?
C30 .1uf 1600v=19.16                ???
C31 .1uf 1600v=OL

Quote
do you want me to put it back together and take live voltage with the probe?
If you are confident making the measurements safely we can go ahead.

A couple of things though:
-  You probably want to force you meter to be on the 6V DC range.   At least that way the measurement will be in kV (so 1V = 1000V)   If it's bobbling around the scales it harder to interpret the results.

- Before you measure the HV measure a 200V rail and a 400V rail and make sure you are getting 0.2V and 0.4V measurements respectively.   If not, do not continue as there is something wrong with the setup or the probe.

Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 19, 2018, 01:13:45 AM
Maybe consider using you old meter first?
Then repeat with the new if all looks ok?
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 19, 2018, 01:15:30 AM
Quote
I haven't read through the whole thread, but it would be pretty sucky to go through all this trouble and find out the CRT is dead.  Do you at least see the heater lighting up?  Assuming it's not obscured by the cathode, socket, yoke or something.

Another really annoying possibility is someone has broken a pin on the CRT.

I wouldn't like to check at this point as we may break it by accident trying to look at it!.
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 19, 2018, 01:17:27 AM
ok just to be sure where can I find the 200 and 400 v rails
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 19, 2018, 01:30:28 AM
ok useing C33 for voltage
235v with meter set on 00.00 =.24
set on 000.0  =.2

424v meter set on 00.00 =.43
meter set on 000.0 =.4

useing probe
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 19, 2018, 01:32:47 AM
Quote
ok just to be sure where can I find the 200 and 400 v rails

You found some back in post #106.

The 400V rail is from C33A. 

Quote
V7pin7   c33A  =  425v
B+a           C33D  =  160v
B+b [V]   C33C  =  348v
B+c [H]   C33B  =  373v

The 400V on C33A and the 160V on C33D would be fine.
It might be less cramped measuring this on the resistors.

You might want to get more exact values for those voltages by measuring with your DMM.
After that measure with the 1.5kV probe and check they match up.

The whole idea is to make sure both measure the same voltage and that nothing has changed since the other day when we checked the 1.5kV probe.   It's a good idea to verify things like 1.5kV probes.
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 19, 2018, 01:35:56 AM
Quote
ok useing C33 for voltage
235v with meter set on 00.00 =.24
set on 000.0  =.2

424v meter set on 00.00 =.43
meter set on 000.0 =.4

useing probe
You beat me to it.

Those results look good:
Probe 0.43V => measured voltage = 0.43kV = 430V   (1.4% high)
Probe 0.24V => measured voltage = 0.24kV = 240V  (2.1% high)
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 19, 2018, 01:39:53 AM
Great, waiting further instructions. sorry I don't spell so good.
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 19, 2018, 01:42:49 AM
I seen on the bottom of the one schematic you posted. all resistors are 1/2 watt unless marked different.
So I would go with 1 wat to be safe, will this work? will not change any resisters till we get it working.
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 19, 2018, 01:52:16 AM
Quote
I seen on the bottom of the one schematic you posted. all resistors are 1/2 watt unless marked different.
So I would go with 1 wat to be safe, will this work? will not change any resisters till we get it working.
Yes, hold off on any resistors replacements at this point.
The test with 9V battery didn't show up anything to be concerned about.
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 19, 2018, 02:03:44 AM
Quote
Great, waiting further instructions. sorry I don't spell so good.

OK.
So we will check some of the HV voltages.  I'm purposely not checking the voltage on either side of R63 at this point.  All the other voltages I've marked have some sort of resistance in series with them to limit mishaps.

So,
- Check the ground lead on the 1.5kV probe is attached well to the chassis of the CRO and make sure it won't get knocked off during the measurements.
- Connect the probe to the multimeter COM (-) and meter V(+) inputs.
- Don't touch the meter or the connections during the measurement.
- Set the meter to 6V DC.   Force the range if possible.
- Set the Focus pot to mid position
- Power-up the unit
- Set the Intensity pot to mid position.
- wait about 30 secs to a minute for the unit to warm up
- measure the six voltages marked in blue on the diagram below.
- turn off the CRO.
- remove the mains plug
- wait about 30 secs to a minute and removed the 1.5kV probe ground connector.
- If anything weird happens like smoke, fizzling noises, sounds of arcing. stop the test immediately,
  turn off the CRO and remove the mains plug.   Tell me what happened and we'll take it from there.

(https://i.postimg.cc/p5T3jjLF/HV-test-pt1.png) (https://postimg.cc/p5T3jjLF)
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 19, 2018, 02:30:57 AM
probe is working can test C33 a-b -c-d
getting 0 on all test points


V57 =0
V58 =
V59 =
V60 =
V62 =
VCRT4 =
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 19, 2018, 02:35:59 AM
just tried with old meter same results
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 19, 2018, 02:51:00 AM
if i probe the 400v rail I get .43
If i probe any test points I get 0
Hooked up meter like post 170
there is power there= 1.034 set on auto
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 19, 2018, 02:54:16 AM
if there was some thing wrong with probe
how can i get the 400v rail to measure?
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 19, 2018, 03:01:23 AM
Quote
probe is working can test C33 a-b -c-d

Quote
just tried with old meter same results

It's good you checked those because it makes the numbers more believable.

So power down the unit and remove the mains plug.
Wait about 1 min or so.

I'm not sure if you actually got a resistance measurement for V8 pin 5 to ground and V8 pin 4 to ground.
A good measurement there will help at this stage.  Perhaps V7 pin 6 to ground and V7 pin 1 to ground.
For sake of removing ambiguity pull V8 and V7 for the test.



Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 19, 2018, 03:04:19 AM
Quote
Hooked up meter like post 170
there is power there= 1.034 set on auto
I didn't get what you were saying here.

Quote
if there was some thing wrong with probe
how can i get the 400v rail to measure?
That's the point of measuring the 400V line.
The probe measurement looks good.
It's not only close it is measuring quite accurately.
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 19, 2018, 03:08:49 AM
V8 pin 4 OL
pin 5  = 1.8
V7
pin1 =all over the place
pin 6 =.1
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 19, 2018, 03:10:51 AM
Quote
V8 pin 4 OL
pin 5  = 1.8
V7
pin1 =all over the place
pin 6 =.1

Were they ohms, k ohms or M ohms?  (makes a big difference)
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 19, 2018, 03:11:21 AM
back when we tested for the 550 to see if the transformer was bad
If you are confident about taking a measurement, the voltage across R57 would be a good indicator.
- Turn off the unit.
- Wait about 1min
- Set the meter to 1000V DC scale.
- Make sure the meter leads are in the COM and V terminals
- Wire the meter to R57 (the side that goes to the Focus pot) and ground
- Power up the unit and take the measurement.
   (- You expect about 550V)
- Turn off the unit 
- Wait about 1min

Be careful!
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 19, 2018, 03:12:24 AM
sorry k ohms
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 19, 2018, 03:18:26 AM
Quote
back when we tested for the 550 to see if the transformer was bad
OK.   Well if you were getting 1V with just the meter it is 1V but with the 1.5kV probe
you will see 1V / 1000 = 0.001 kV  so it might show up as 0.000 or 0.001.

Quote
sorry k ohms
Hmm, well those measurements don't look promising.
Another check would be to measure the resistance *between* V8 pin 4 and V8 pin 5.
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 19, 2018, 03:23:10 AM
v8
pin 4 to pin 5 =OL
v7
pin 1 to pin 6 = all over the place
Title: Re: help with oscilloscope model 34
Post by: thermionix on October 19, 2018, 03:35:45 AM
Quote
I haven't read through the whole thread, but it would be pretty sucky to go through all this trouble and find out the CRT is dead.  Do you at least see the heater lighting up?  Assuming it's not obscured by the cathode, socket, yoke or something.

I think he mentioned it was lighting up very early in the thread.  Maybe even in his other thread where be bought the equipment. see post #3 and post# 10

My bad.  Ignore me.  Carry on.
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 19, 2018, 03:37:26 AM
Quote
v8
pin 4 to pin 5 =OL
That implies the heater winding has gone.   
Your previous result that pin 4 is OL would imply that it is the winding going to pin 4.

When the unit is running can you see the heater of V8 operating?
From what I remember it was hard to see those heaters working.

Quote
v7
pin 1 to pin 6 = all over the place
That's not good.  It agrees with your previous measurement that pin 1 to ground is all over the place.
That's implying the winding from pin 1 to ground has failed.

We are getting 430V DC but it's only half-wave rectified and is only utilizing one side of the winding.

Title: Re: help with oscilloscope model 34
Post by: whomeno on October 19, 2018, 03:39:53 AM
ok, so how much would it cost to replace.
More then it is worth right
How would I know what to replace it with even
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 19, 2018, 03:44:17 AM
v7 is lit
v8 no more
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 19, 2018, 03:47:45 AM
I got a quick question about something else.
I am going to build a tonepad mctube with a 12ax7.
I think you answered this before but can't find it
would this transformer work
https://www.tubesandmore.com/products/transformer-power-125-v-15-ma
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 19, 2018, 04:01:58 AM
Quote
ok, so how much would it cost to replace.
More then it is worth right
How would I know what to replace it with even
My gut feeling is that. 

However, it would need some research. You never know what you find.

Sometimes you find people selling second hand transformers from the same model oscilloscope.
The problem with these is they could work today and fail tomorrow.  Pot luck but better than nothing

Another pot luck solution is to get another unit cheap and use it for parts.   No guarantee the transformer in that unit is any good either.

If you had to get one made I suspect it would cost a lot.

Another option would be to adapt an existing transformer.  You would probably have to redesign
some of the power supply to do that.

You could turn things around and see that unit for parts.  One issue is you don't know the CRT is good.

Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 19, 2018, 04:07:27 AM
Quote
I got a quick question about something else.
I am going to build a tonepad mctube with a 12ax7.
I think you answered this before but can't find it
would this transformer work
https://www.tubesandmore.com/products/transformer-power-125-v-15-ma
It won't work directly. 

This come-up in another thread within the last month or so.
(To me) the issue is the transformer voltage is going to produce a high-voltage DC rail which exceeds
the 150V/160V rating on the caps.  You will need to add a dropping resistor (with appropriate power and voltage ratings), possibly even a voltage divider, on the high voltage winding.   
Alternatively, you could use higher voltage caps but then all the voltages are out and you might have to tweak the circuit a bit.   Also it's not quite the same thing as it was before.
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 19, 2018, 04:07:36 AM
That was my thinking try and sell it for parts.
Would i need one if i try to build an amp?
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 19, 2018, 04:09:38 AM
ok if I go the 2 transformer route would these ones be ok to use?
https://www.mouser.com/ProductDetail/Triad-Magnetics/F-113X?qs=A0MODW4pnbR3qV1G9EWZYQ%3D%3D&gclid=CjwKCAjwu5veBRBBEiwAFTqDwc0r1RviKAbPNR4Iu5jhZrIGahC92p0ADnX3SXYq4Kl3uKGbbbVmUhoCMIUQAvD_BwE
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 19, 2018, 04:14:12 AM
I know i am a pain in the butt. my wife tells me that all the time! I want to thank you for taking the time working on this.
I have learned a lot, but I need to learn a lot more.
Thanks Rob
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 19, 2018, 04:14:17 AM
Quote
That was my thinking try and sell it for parts.
Would i need one if i try to build an amp?
You can go a long way taking DC measurements however there's some problems which are really hard to solve without a CRO.  One is oscillation.  If an amp oscillates you can see it quite clearly on the CRO.  Without a CRO you have to use a lot of guess work and tinkering; even then with dubious results.

It is possible to use a sound card but it's usually not good enough to solve oscillation problems.   The devices PRR mentioned very early in this thread are quite cheap and are probably good enough to get by.    Yet another option is second hand stuff but then you don't always come out on top.  Like your current case.
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 19, 2018, 04:18:28 AM
Quote
ok if I go the 2 transformer route would these ones be ok to use?
I wouldn't like to use those since they are only 0.15A secondaries.   The rating is a bit marginal when we consider the rectified and filtered heaters.  I think you should aim for at least 0.3A secondaries.   The original  effectively had 0.5A secondaries.
Title: Re: help with oscilloscope model 34
Post by: Rob Strand on October 19, 2018, 04:19:43 AM
Quote
I know i am a pain in the butt. my wife tells me that all the time! I want to thank you for taking the time working on this.
I have learned a lot, but I need to learn a lot more.
Thanks Rob
No problem at all.  I'm happy you survived!
Title: Re: help with oscilloscope model 34
Post by: whomeno on October 19, 2018, 04:21:35 AM
ok i see where i need to focus now  0.5A secondaries.
Thanks again
Rob