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MU524 Vari-Mu Tube Compressor / Re: Low output voltage step 6

« Last post by JPK on Today at 06:49:12 PM »

TP2=  0.057 VDC
Here is the issue. You should get around 30VDC.
You must check the solder joints on R7, on the tube socket, on the connector that links the tube PCB to the main PCB.
Check that the 48V gets to both sides of R7 (you can check without the tube inserted).

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MU524 Vari-Mu Tube Compressor / Re: Low output voltage step 6

« Last post by Ben on April 07, 2026, 04:22:11 PM »

Sure can, 
TP2= 0.297 VAC and 0.057 VDC
TP3= 0.077 VAC and 0 VDC

Pot 1, R1 and R2 test ok as well
Thanks,
Ben

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MU524 Vari-Mu Tube Compressor / Re: Low output voltage step 6

« Last post by JPK on April 07, 2026, 09:04:14 AM »

Can you please also report the values on TP2 and TP3?

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MU524 Vari-Mu Tube Compressor / Re: Low output voltage step 6

« Last post by Ben on April 03, 2026, 05:05:53 PM »

I reheated all solder joints and rechecked for bridging or shorts, no change
Thanks,
Ben

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MU524 Vari-Mu Tube Compressor / Re: Low output voltage step 6

« Last post by Ben on April 01, 2026, 07:50:42 PM »

 0.05vac and 29.69vdc @ TP1
0.077vac and .258vdc @ TP4

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CP554 Diode bridge compressor / Re: Cant get 3v at step 5

« Last post by JPK on April 01, 2026, 05:46:35 PM »

Check the solder joint on D20.
If solder joints are OK try to replace D20 (Zener 4V7-1.3W).

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CP554 Diode bridge compressor / Re: Cant get 3v at step 5

« Last post by vwyf11 on March 30, 2026, 07:18:47 PM »

No, the voltage from tp3 to 0v is not stable.  It bounces around from -10 to -12.5 very erratically.  I’ve tried tapping around and checking at each component or the pcb but nothing seems to directly affect the erratic nature of the voltage readings.  It seems it’s getting even worse.  The readings are jumping instantaneously from 0v to 4.5v when measuring between tp2 and tp3.  Measuring the voltage at the card extender is a steady 15.5 volts + and -

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CP554 Diode bridge compressor / Re: Cant get 3v at step 5

« Last post by JPK on March 30, 2026, 11:19:39 AM »

The diodes D10, D11 on the front PCB have no effect on the the output stage bias setting.
Is the voltage on TP3, against 0V stable, around -11.5V ?
Is the bias voltage bouncing when you tap the PCB or specific components with a pen ?

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CP554 Diode bridge compressor / Re: Cant get 3v at step 5

« Last post by vwyf11 on March 29, 2026, 07:42:40 PM »

When I installed the diodes I was able to get a solid 3v between tp2 and tp3.  After this step I had double checked the next day and am back to not being able to get a steady 3v from tp2 to tp3.  The meter bounces around from 2.4 or so volts to 2.8v.  I cannot even get to 3v anymore. I’ve ripped everything apart and double checked everything now.  Tried reflowing parts, nothing seems to be working.  

The voltage from 0v to V+ and V- both give me steady correct voltage.  

All the other tests on the page you link to are giving me results in the ballpark for the required voltages but all fluctuate around 0.25v up or down from the target voltage

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MU524 Vari-Mu Tube Compressor / Re: Low output voltage step 6

« Last post by JPK on March 27, 2026, 04:08:55 PM »

Remove U4.
What values (DC and AC) do you get on TP1 to TP4 in the initial conditions here.