Hi!
I'm restoring a Moog Realistic MG-1 analog synthesizer that I recently acquired. It wasn't working when I bought it, but that turned out to be due to bad solder joints, so things are good now. Everything works beautifully. Except...
When probing some signals with my scope I noticed that the ground of the synth - including the chassis - has a pretty large, about 27V p-p, 60Hz AC component (relative to mains ground; see attachment). Consequently all signals, when measured, has this rather large signal overlaid as well. The unit is NOT mains grounded: It has a two prong power cord ('three prong-style' with the ground pin plugged) which I believe is actually original and not a hack (see attached photo).
I've included the PSU schematic from the service manual - I imagine that's where the problem lies. Initial probing didn't reveal anything completely unexpected (to me, anyway) though I admit this is not really my area of expertise.
Any good ideas where to look next?