70's Roland JC120 (CH1 Sawtooth)

[g1]

Sometimes grounding faults will show as 120Hz ripple somewhere. I see a grounding screw holding down that Ch.1 board, make sure it is tight and you may even want to clean the trace underneath. You should be able to do that by removing the screw and pulling up on the board a bit. Get a piece of sandpaper between the screw turret and the trace and scuff it up a bit. Also make sure the pot nuts and jacks are tight.
The power switch up/down is a polarity (grounding) switch. That it makes a difference backs up the idea that it may be a grounding issue.

Note that for schematics and layouts, we are referring to post #7 schems., pg.6 and 7.

[dubulup]

Upon inspection the traces...I saw a pad that was totally MIA! found an unused GND connection for C23 and we are singing again!

Many thanks for providing the schematics and tips!

[g1]

Your photo with the added jumper only shows you making the connection on one side, did you also repair the trace going from the other side?

[Delta362]

I agree with g1. While your jumper connected the missing pad of the left component to the component below it, it looks like it might not be making a solid connection to the component on the trace to the right.

[dubulup]

That's why I love this forum! I went back in (too excited to test) and there is only one component installed downstream of C23 on the CH1 board...R18. It still had GND continuity but as you mention...no telling how solid that connection was with that broken pad, so I solidified R18 with a jumper. Is it a safe assumption there are no internal multi-layered traces on boards this old...not even a ground plane, ha!

[Delta362]

I don't think these boards have any more traces other than the bottom side.

Edit: Removed top side trace comment