At this point you know the problem is on the main board. If you lift the output leg of 7912 do you have a -12 volts? If so there are a handful of IC'S,Transistors,which include the LM361, not the 14060 I mentioned previously, because this IC only uses the +12 volt regulator.
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The -12 volt regulator supplies the SUB1 & SUB 2 board and the remote gain control circuit (Q510-KTC3198GR) plus the pull up supply(-2 volts) for the U101- LM36 (Q106-KTA1023y and D105-ISS133). Also Triangle wave gen circuit (Q102-KTC3198GR).
There is also a possibility that one of the caps across the -12 volt supply is shorted,check C779,C780 if you haven't done so.
1:Inspect the remote gain control socket (MOD1) for shorted pins.
2:Check with an Ohmmeter/diode checker all transistors, diodes,caps around Q510 and Q106.
3:Remove Sub1 and Sub2 boards one at a time and check to see if -12volts comes up with out burning R772.
The remote gain control circuit is a common issue so, carefully inspect the board, especially for signs of moisture.If one of the SUB boards prove to be the culprit I will advice further at that time.
My time here on DIYAudio is limited as I am occupied with other matters. I will respond when I'm able. In the meantime there may be others here who can offer good advice, namely Perry Babin which I'm sure your aware of.
There is also a possibility that one of the caps across the -12 volt supply is shorted,check C779,C780 if you haven't done so.
1:Inspect the remote gain control socket (MOD1) for shorted pins.
2:Check with an Ohmmeter/diode checker all transistors, diodes,caps around Q510 and Q106.
3:Remove Sub1 and Sub2 boards one at a time and check to see if -12volts comes up with out burning R772.
The remote gain control circuit is a common issue so, carefully inspect the board, especially for signs of moisture.If one of the SUB boards prove to be the culprit I will advice further at that time.
My time here on DIYAudio is limited as I am occupied with other matters. I will respond when I'm able. In the meantime there may be others here who can offer good advice, namely Perry Babin which I'm sure your aware of.
The -12 volts is tied to pin 1 of HP2 on the SUB1 board, The Signal Ground is the adjacent pin, pin 2 of the same board and pin groupings. The -12 volts is applied to the collector of Q71-KTA1661y.
Measure pins 1 and 2 with an ohmmeter for shorts. Also, check the pins of Q71 for the same. Examine the Sub1 board for and solder bridges, wire clippings or anything that might cause a short.
Keep in mind it's possible removing the board may have removed any shorted pins.
Measure pins 1 and 2 with an ohmmeter for shorts. Also, check the pins of Q71 for the same. Examine the Sub1 board for and solder bridges, wire clippings or anything that might cause a short.
Keep in mind it's possible removing the board may have removed any shorted pins.
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