Discussion about the Korg PolySix synthesizer

Well I'm happy to report that I made some progress.

Starting with my main Polysix:

I was able to test the power supply as you suggested. It checks out fine at all the test points: +/- 4.95 V and +/- 14.96 V.

I went through the KLM-367A and replaced it with a fresh battery. My battery mod was done about 15 years ago and it appears that the original mod never included the 1N914 and cap removal so I did that. I also re-checked the continuity for IC26, IC30, IC31, and IC32. Everything appeared to be working. Since I had the 367A out I gave it a thorough cleaning too and double checked the solder joints in key areas. I reflowed a few spots for good measure in kew areas on the card as well as on the MG board. All in all I didn't make major sweeping changes but I somehow managed to get rid of that intermittent MG level. Unfortunately I'm not certain how that was achieved. I did lose the original patch data though by keeping the battery out long enough. I also removed the 8048 and tried two others to test their integrity. Perhaps all this had some effect. It also doesn't seem to detune as heavily as before either so I just don't know what changed it so drastically! The clean up and tune was well worth it though. It feels like a fresher instrument. Time will tell. I'm watching and listening to it closely.