RetroFit - First-aid for Keyboards!

What it’s all about...

A few years ago I bought a Polymoog ‘spares or repair’, confident in my ability to repair it and then play it for my own pleasure and that of others.

Unfortunately the MM5823N required for its repair, although used extensively in the 70s and 80s, ceased to be produced some time ago, thus rendering my Polymoog only good for spares.

Or so I thought.

Not being the type to give up easily, I managed to get a datasheet for the MM5823N and found that, whilst strangely it used negative supply, the actual divided outputs didn’t. This meant that it would be possible to use standard CMOS parts, which have equivalent supply voltages (just not negative ones) to make a replacement chip.

So I did.

Here’s a picture of the first one...made by my own fair hands and attached to the Polymoog divider board.

Then I realised that there might be other people out there wanting to repair their kit, so I set about making replacement chips of several types, smaller and neater too!

Click on the links at left to see what's on offer!

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