[sdiy] Ground loop problem with Polysix

[Sean Ellis]

After several months I finally got my sick polysix working! I'm thrilled but 
it has a bad problem with ground hum when the power cable is plugged in. If 
I remove the back panel bracket from the case the hum goes away but fully 
isolating it will be a pain. The 2 audio output jacks are isolated plastic 
types and no connection to the bracket is being made. Has anyone noticed 
this before with a polysix and could give me some pointers on where to look? 
My model has the thick ground cable going from near the battery to the front 
panel board.

BTW thanks to the 2 list members who helped with parts, I removed all the 
keys and front panel components and gave the synth a complete physical 
overhaul. Looks almost like new now :) Just need to replace the front panel 
switches since 2 are barely functioning.