Author Topic: help with oscilloscope model 34  (Read 9273 times)

Rob Strand

Re: help with oscilloscope model 34
« Reply #160 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.
The mind often distorts without gain.

Rob Strand

Re: help with oscilloscope model 34
« Reply #161 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.
The mind often distorts without gain.

Rob Strand

Re: help with oscilloscope model 34
« Reply #162 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.
« Last Edit: October 18, 2018, 07:18:55 PM by Rob Strand »
The mind often distorts without gain.

whomeno

Re: help with oscilloscope model 34
« Reply #163 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
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Rob Strand

Re: help with oscilloscope model 34
« Reply #164 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.
The mind often distorts without gain.

whomeno

Re: help with oscilloscope model 34
« Reply #165 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
Gear as of now
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Peavey valveking2

whomeno

Re: help with oscilloscope model 34
« Reply #166 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?
Gear as of now
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Marshall DSL40cr
Peavey valveking2

whomeno

Re: help with oscilloscope model 34
« Reply #167 on: October 18, 2018, 09:24:40 PM »
 resistance between V8 pin 4 and pin 5 = open
Gear as of now
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Rob Strand

Re: help with oscilloscope model 34
« Reply #168 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.


« Last Edit: October 18, 2018, 09:36:03 PM by Rob Strand »
The mind often distorts without gain.

whomeno

Re: help with oscilloscope model 34
« Reply #169 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
Gear as of now
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Marshall DSL40cr
Peavey valveking2

Rob Strand

Re: help with oscilloscope model 34
« Reply #170 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!

The mind often distorts without gain.

whomeno

Re: help with oscilloscope model 34
« Reply #171 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
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Rob Strand

Re: help with oscilloscope model 34
« Reply #172 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:


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.

« Last Edit: October 18, 2018, 10:57:49 PM by Rob Strand »
The mind often distorts without gain.

whomeno

Re: help with oscilloscope model 34
« Reply #173 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
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whomeno

Re: help with oscilloscope model 34
« Reply #174 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?
Gear as of now
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Rob Strand

Re: help with oscilloscope model 34
« Reply #175 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.
The mind often distorts without gain.

whomeno

Re: help with oscilloscope model 34
« Reply #176 on: October 18, 2018, 10:49:41 PM »
ok
Gear as of now
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Rob Strand

Re: help with oscilloscope model 34
« Reply #177 on: October 18, 2018, 10:55:31 PM »
I've added the test pic to the previous post.
The mind often distorts without gain.

whomeno

Re: help with oscilloscope model 34
« Reply #178 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
Gear as of now
Gibson 2017 Les Paul Tribute T
Marshall DSL40cr
Peavey valveking2

Rob Strand

Re: help with oscilloscope model 34
« Reply #179 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.

« Last Edit: October 19, 2018, 12:32:29 AM by Rob Strand »
The mind often distorts without gain.