Marshall Valvestate Bi-Chorus 8200 Resource Thread:

67plexi said:
If your running a signal into the efx return no sound it's the amp section at fault.
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The amps sounds fine, when my friend brought it to me it was not sounding at all, upon opening I saw the caps in the power section had swollen, proceeded to change them and in the process I changed all the electrolytic caps as well.
Once I did that the amp came back to life.
When I started inspecting each channel, noticed that the treble in the OD channel, when dimed it was cutting all sound.
So I proceeded to investigate removing resistors in parallel to check if they were open and also changed the other caps, basically the whole eq section has been changed with brand new components except the c9 (capacitor that looks like resistor) that I don’t have in stock.
My last step was to put sockets for the IC and change the ic1 5534a then I swapped around the 5201 within the amp.
 
So I just run a full check of the grounding and all seems healthy, I’m running out of ideas for the treble. One of my first test was to swap the pot vr8 with vr2 that are the same value, but the problem remained, maybe both are bad, but the vr2 position works fine. So I’m clueless here
 
Robert Herndon said:
Awesome!!!!

Please post your details!!!!!
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Sure buddy, I was getting desperate with the eq behavior, so I thought “what if I could go straight from the valve to the IC5534.
Then I started removing parts and looking at the schematic, testing continuity, and it wasn’t making sense in my head every component was testing well outside the circuit and the traces were fine and healthy.
Decided to put everything back in reflowing all the pots not only the problematic ones.
I was about to give up, I plugged in turned it on and viola! It was alive completely with eq and all!
 
Theabducted said:
Sure buddy, I was getting desperate with the eq behavior, so I thought “what if I could go straight from the valve to the IC5534.
Then I started removing parts and looking at the schematic, testing continuity, and it wasn’t making sense in my head every component was testing well outside the circuit and the traces were fine and healthy.
Decided to put everything back in reflowing all the pots not only the problematic ones.
I was about to give up, I plugged in turned it on and viola! It was alive completely with eq and all!
Click to expand...
So, a cold solder joint?
 
Theabducted said:
So I went and asked if they had military grade, their answer was simply, there’s cheap and there’s expensive .
Got the expensive, they were about 0.89aud, so I got 5 and 1x 14pin.
Got home mounted them, changed the 5534, and put back all the 5201a’s and the LM348N the issue is still there.
I got the suspicion that it’ll be c9 that is a 4.7nF cap that looks like a resistor, it is directly connected to the treble pot to ground and it is the only component I haven’t change in that section
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What about the plus / minus 15 volt supplies?
Are the voltages on pin 8 pin 4 of 5532 fairly equal or is one voltage far off spec?

When the problem happens
does the voltage on pin 3 of 5532 go positive?
 
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