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Have you tried unpluging and then plugging it back in? Sometimes a key strategic whack near where you think the problem is located helps... About 50/50 it works🤓

oh man, if it were only that simple with stuff like this... nothing is simple with vintage audio production hardware. I have tried the unplug/re-plug... and taken it apart completely and fuddled with it - out of my ballpark. I focus on production and writing, circuitry is beyond me.

If i had the manual and your # i might be able to help. I used to tech speakers. Not much with amps though. But there is simple things you can do like check resistance on the circut board between connections around the power source.
If the fuse isnt blown then look closer around power source to see if any visable motherboard pins are missing soder. Or maybe a common problem might be the step down transformer(also near power source)
Im sure you already typed in the model # and brand into google with a brief description of the problem.

Yea there is a disabled connection - trust me homie I have no intention of playing operation with solder in that thing or messing with it further. Leaving this one to the experts. I could easily ruin both modules with a tiny mistake - this gear is OOOOOLD - 1960s.