my delta 70 was running OK then one channel suddenly became very very loud. I could only use the amlifier with the balance contol fully clockwise. I isolated the fault to one plug-in board (not the pre-amp board). I have the circuit diagram, but need help to pin poibt the faulty component. I have checked the board for bad solder joints. Any suggestions please.
Looks like the NFB does go through the sockets. Lol... at least they are in the loop 
Make sure (measure on ohms range with amp OFF) that point "A" (measure on R36) goes down to virtually zero ohms at minimum volume. Check that R48 is OK and that all the plus/sockets are good. Many of the electroylitics will be getting past it too and it would all benefit from a re-cap... but find the fault first.
Edit... measure the resistance above with respect to ground (the thick black line).
Make sure (measure on ohms range with amp OFF) that point "A" (measure on R36) goes down to virtually zero ohms at minimum volume. Check that R48 is OK and that all the plus/sockets are good. Many of the electroylitics will be getting past it too and it would all benefit from a re-cap... but find the fault first.
Edit... measure the resistance above with respect to ground (the thick black line).
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