So I recently got a Polymoog 203A (2nd one I’ve had) and of course it wasn’t working. Tempted as I was to just turn it into a coffee table I decided to try to bring it back to life. Probably a dumb and pointless endeavor but first up was getting the power supply working. I only had +15, the -15 and +5 rails were gone. Some of the bridge diodes got a bit toasty and were actually crumbling away -
They were 1N4002s, were they underspec’d and couldnt’ handle the current perhaps? Anyway replaced those and got 1 rail back and it took me a while but I found a 723 regulator in the 10-pin can and that brought back the other dead power rail. After verifying all voltages with the synth boards disconnected I plugged in the power conenctor to the synth and powered her up and got lights and sound!
About 1/3rd of the keys weren’t working so I though uh-oh lots of divider chips to replace but after re-seating some of the boards and working the dirty key contacts I am down to just a handful. The C#, D, and D# keys in the lower 4 octaves don’t have saw waveforms and a couple keys are completely dead. Some troubleshooting and looking at the schems and I think I only have 1 or 2 bad divider chips (ICs 14 and possibly 22 on the divider board if I’m reading the schems correctly) and possibly 2 polycom chips. Swapping polycom chip cards with another key and the problem follows the card. Anyone know of a source for the polycom ICs?
Oh yeah 723 is the regulator, 726 is the VCO… Today it took a step backward as I seem to have lost the Direct signal output. All the other modes work OK but nothing from Direct, any ideas?
Sigh, yeah I know. Actually compared to the Memorymoog it does seem a bit simpler. Does anyone have a scan of part 1 of the Polymoog service manual? I found one for part 2…
I have an original copy of part 1 but never saw a scanned one online. Damn thing reads like a college textbook.
Last known source of the polycom ICs was DB Electronic Music in Buffalo NY. I visited that shop back in 1998 - the guy there used to work at Moog and had a bunch of surplus stuff including the polycom ICs. His AOL page is 404 and I’m not sure he is still around.
Awful looking cracked up diodes shown here… What’s the serial number of this machine?
Keep us posted on new developments.
Luckily, my own Poly was pretty clean and around 80% functional when I got it. Simply bringing it back home, it fell down around 50%. I removed all the boards, cleaned it up. I did not replace any parts. Went back up to 90%, rough estimate. All keys are working, and most presets. I played it only a couple of times, put it back into storage, waiting for better days (and to find a proper technician to work on it).
Reading all over, I am less confident that day will ever come, but still hopeful.
Yeah that looks like the Faratron power supply used in the first generation of Polymoogs before Moog designed their own power supply.
Good to hear that Besecker is still in business.
I fired up my Polymoog and it has developed some new problems. It’s one of the last units and has gone THIS LONG with few problems. Oh the joy of synth maintenance This is what is under the hood of a Polymoog (there are another set of boards under the top ones)
Not sure I came across this page before but very interesting reading, Thanks for the link. Not sure it makes me feel any better
I got the poly pedals too. I don’t know much about them, I never plugged them into the poly. I always thought I could use them somehow to control the D or other vintages. Any thoughts on that?
All right, thanks for the tip. I do have a DIY power supply with +5, -5, +12, -12, +15, -15 power rails that I use for the 1130 among other things. Pretty much loaded at work ATM, yet I can’t get my mind off little circuit things. Time to print out some docs
Not a slam, but an honest question: Do you know of any actual differences between the Moog power supply and the Faratron?
I’m not sure I remember any, but if the Faratrons are older, that alone could be cause for greater failures.
Yup, service bulletin #1207 does list some corrections to the Faratron supply including a PCB etch error that made it vulnerable to overvoltage conditions. That definitely may had blown some Polymoogs. Will scan the pages and upload soon.
None of the 14-preset Polymoog Keyboards had the Faratron, only the 8-preset version up to serial 3200 had the Faratrons.
Does anyone have a scan of part 1 of the Polymoog service manual? I found one for part 2…