Polymoog 203a repair

Synth Repair
1

Hello everyone,

I was recently given a nonfunctional Polymoog 203A. While I’ve never repaired a synthesizer before, I have some experience working on home audio amplifiers and receivers.

When I power it on, the only sound I get is a low hum. Additionally, when I touch certain knobs, the hum becomes louder, which makes me suspect a potential grounding issue.

I also noticed a missing chip on the top-leftmost board. Based on the schematic, it’s labelled as IC8, but I haven’t been able to identify which chip belongs there.

So far, I’ve started cleaning components, following safety guidance from my mentor, who built a synth using breadboards from scratch. However, I’m struggling to find clear information on replacement parts in the schematics.

Does anyone have suggestions on:

  • How to identify the missing IC8 chip?
  • Common ground issues in the 203A that might cause this hum?
  • Best practices for locating replacement part information?

Any help or insights would be greatly appreciated.

Thank you!

Edit 1: so far I have only cleaned the “Polycom chips” and removable plugins on the board above them.

2

The first thing to know: the Polymoog with its many unbuffered CMOS chips is extremely sensitive to electrostatic discharging. Don’t work on it without proper grounded hands. Don’t wear clothes from wool, don’t wear synthetic clothes.

To identify the IC8 → get the servicemanual. E.G. from my page: https://www.florian-anwander.de/moog_polymoog/polymoog_service_manual.pdf

Then the absolutely first thing to do on a polymoog is getting the powersupply to work properly!

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