Author Topic: help with oscilloscope model 34  (Read 9272 times)

whomeno

Re: help with oscilloscope model 34
« Reply #200 on: October 19, 2018, 02:35:59 AM »
just tried with old meter same results
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whomeno

Re: help with oscilloscope model 34
« Reply #201 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
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whomeno

Re: help with oscilloscope model 34
« Reply #202 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?
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Rob Strand

Re: help with oscilloscope model 34
« Reply #203 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.



« Last Edit: October 19, 2018, 03:04:37 AM by Rob Strand »
The mind often distorts without gain.

Rob Strand

Re: help with oscilloscope model 34
« Reply #204 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.
The mind often distorts without gain.

whomeno

Re: help with oscilloscope model 34
« Reply #205 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
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Rob Strand

Re: help with oscilloscope model 34
« Reply #206 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)
The mind often distorts without gain.

whomeno

Re: help with oscilloscope model 34
« Reply #207 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!
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whomeno

Re: help with oscilloscope model 34
« Reply #208 on: October 19, 2018, 03:12:24 AM »
sorry k ohms
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Rob Strand

Re: help with oscilloscope model 34
« Reply #209 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.
The mind often distorts without gain.

whomeno

Re: help with oscilloscope model 34
« Reply #210 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
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thermionix

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Re: help with oscilloscope model 34
« Reply #211 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.

Rob Strand

Re: help with oscilloscope model 34
« Reply #212 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.

The mind often distorts without gain.

whomeno

Re: help with oscilloscope model 34
« Reply #213 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
« Last Edit: October 19, 2018, 03:41:24 AM by whomeno »
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whomeno

Re: help with oscilloscope model 34
« Reply #214 on: October 19, 2018, 03:44:17 AM »
v7 is lit
v8 no more
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whomeno

Re: help with oscilloscope model 34
« Reply #215 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
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Rob Strand

Re: help with oscilloscope model 34
« Reply #216 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.

The mind often distorts without gain.

Rob Strand

Re: help with oscilloscope model 34
« Reply #217 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.
The mind often distorts without gain.

whomeno

Re: help with oscilloscope model 34
« Reply #218 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?
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whomeno

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