poly61m deathsmell fix

I’d been working on a track and moved a bunch of stuff around, including my battered Poly61M. After recording I turned everything off for the night. And mistakenly left the Korg on.

I woke up at about 3am thinking “what’s that godawful smell?”

Dead Poly61m safety capacitor on PSU board

Yeah, that looks wrong doesn’t it?

Mmmm, 30-plus years of dust. In the middle we have a bulging Rifa 33nF paper capacitor. It doesn’t smell very nice.

The synth still works, but worryingly the power switch doesn’t actually turn it off any more, so the capacitor has failed short.

I found the recommended replacement according to the Rifa datasheet – here’s the bottom of the old burned-up one on the left and the new one on the right.

Poly61M burned capacitor

…and now it works fine again: boring fix, sorry everyone.

Here are some random photos of the inside. I had to take the keyboard out to get the power supply board out, gahhh

Poly61M PSU board

Here’s the main voice board, socketed SSM2056 and all

Poly61M main board

And this is probably the main processor board – there’s another board wonkily attached for MIDI on the left which I cleverly didn’t get a photo of.

Poly61M processor board

Yes, the 80s:

Poly61M hot pink

The electrolytic capacitors in the power supply could probably do with replacing – as could the tactile switches on the front panel – but that’s a job for another day.

Oh and the keyboard barely works as well, which is standard with these. I’ve been in it before to try and fix it but they always die again, it’s one of those inherently shit designs. Good thing it’s the M version and I can control it externally.

I managed to threaten a few keys into action by banging seven bells out of it – here’s me absent-mindedly stepping through some presets and CLICK-CLICK-CLICKING the half-dead buttons.

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  1. 29th June 2020Kevin says:

    Those Rifa X2 caps are notorious. I had one fail in exactly the same way in my DX7. They are also found in the power supplies of BBC Micros, though in this case they are across the mains and always seem to fail open – the machine carries on running quite happily as the room fills with smoke,

  2. 10th April 2022Charlie says:

    Hi Would you mind if I ask what kind of Rifa capacitor should I get?

  3. 10th April 2022ua726 says:

    I wasn’t sure either, so I’ll show my working – the code on the size of the capacitor I whipped out was:


    labelled as Rifa 0.033uF, 250V.

    I found the datasheet for it: http://www.wima.com.ua/image/catalog/pdf/e5f87de61ec3874b2e2b1ea4ac7cb0ac-EVOXS00054-1.pdf

    …and the suggestion in there was to replace it with PME271Y (300VAC), so that’s what I ordered and put in, and it’s been alright ever since.

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