Korg Polysix Repairs

[creatorlars]

Please let me know if this topic needs to be moved, I wasn't sure where else to post.

My friend just purchased a Korg Polysix off eBay and it's got some issues. I messed with it some last night and opened it up to take a look. Appearance-wise it's beautiful and clean, both inside and out.

Aside from some obviously easy stuff, like tuning up the oscillators, there seem to be some issues with the controls. The ADSR, filter, modulation and LFO controls are all ineffective at producing any change in sound at all.

I think I am correct in assuming that this synth uses a microprocessor to control the analogue components, so I am guessing the problem lies somewhere in the control board. There are 6 SSM2044s for the filters, and it doesn't seem likely that they could all be out. All six oscillators appear to be working. The stored patches load up and produce changes in sound -- but the envelope still appears to have no effect on the amp or filter, and I can't seem to hear the filter in action. Bend & Mod wheels produce no effect either. Since a few of the top panel controls appear to work fine and everything looks clean inside -- it doesn't seem like an issue with dead pots, but rather in the control interface somewhere. Power supply voltages check out okay. Arpeggiator works correctly with no issues.

Before I dismantle everything and frustrate myself, I was wondering if anyone here has clues on this? It sounds like something potentially simple. Could this have to do with the internal battery? Or a dead microprocessor? Are these symptoms pointing to a known issue with this synth?

Please advise!

Thanks,
Lars

[neandrewthal]

Is the big blue battery still on the control board? Are you sure there is no corrosion around it? Those things love to leak.

[EdisonRex]

Do the preset buttons latch, and only one lights at a time? Can you put it in manual mode?

Is the sound you are getting the default triangle sound?

The battery is highly suspect.

[richardc64]

This may or may not help:

http://www.oldcrows.net/~oldcrow/synth/korg/polysix/index.html

[rjd2]

im curious as well on this. i have a yamaha cs-40m that has 2 controls that dont function, but the actual pots work fine. the controls are read as 100% open pot, if you will. i am told that it is probably a multiplexer chip, but i have yet to source the chip(my amateur attempt at reading schematic hasnt found it). let me know what you come up with.

[scriptstyle]

i have a yamaha cs60 that has some issues i need to get to when i get some spare time. i kinda remember stumbling on a page where some one pulled the psu out of one and threw it in a tool box once, sound familiar?

[creatorlars]

Hey, thanks for the tips!!

I got it working last night. The battery seemed to definitely be the most suspect problem-area, after reading up on the leakage issues and referring back to my symptoms. After a second look, though -- it seemed as if the battery had already been swapped out with the coin lithium type, as detailed in oldcrow's site. The battery holder's mounting job seemed a little sloppy though. I positioned it a little bit more solidly and swapped out the battery with one I bought at the local Radio Shack. It powered up and appeared to still be broken, but after warming up for a few minutes, everything began to function correctly! I only wish I had an oscilloscope, so that I could tune everything back up to factory presets (the oscillators were way out of tune.)

Damn those SSM2044 filters are BEAUTIFUL!!

Anyway, thanks for the help.

[solidstate06]

I hate to disappoint you, but it sounds like you´ve still got something wrong with that Polysix. It should not take a few minutes of warming up to get it working properly. Replacing the battery was correct, but to me it sounds like you still got some problems with broken/corroded pcb traces around IC30/31 and the CPU. Almost EVERY old P6 suffers from that problem. I´ve repaired a few of them and even though I´ve repaired all the broken traces I could find at one given time, even more traces have broke months later, requiring further repair...

[creatorlars]

Well, when I referred to warming up, I meant only once, after replacing the battery. It turns on and works immediately now. I will definitely take the board out and examine it for broken traces if she experiences any regression or further issues. Thanks for the help.