I think your problem is that you are a bit stubborn to be honest. When Wakh and anatech say you should try replacing or disconnecting this capacitor, there is thinking behind it. Leaving the cap for now, there is no thinking behind that.
Just disconnect that cap C1 and see if that works!
The capacitor Wakh is talking about in post #671 , I think is the blue one in this picture:
https://www.diyaudio.com/community/attachments/1704426534462-jpeg.1255752/
Maybe others could check this also.
This capacitor looks different than the others on the board, I think it is more recent, it may have been replaced in the past.
It has a + and a - side. Take it out and remember where the + and - were. Put it aside. Now measure voltage of your circuit: put red probe where the - of the capacitor was, black probe on ground (- of power supply). Now you should measure about 27 volts, maybe you have to adjust the potmeter.
https://www.diyaudio.com/community/attachments/1704426534462-jpeg.1255752/
Maybe others could check this also.
This capacitor looks different than the others on the board, I think it is more recent, it may have been replaced in the past.
It has a + and a - side. Take it out and remember where the + and - were. Put it aside. Now measure voltage of your circuit: put red probe where the - of the capacitor was, black probe on ground (- of power supply). Now you should measure about 27 volts, maybe you have to adjust the potmeter.
+ and - are correct.
Where did you measure 12V?
On the plus side, on the minus side, or did you measure between them?
Where did you measure 12V?
On the plus side, on the minus side, or did you measure between them?