Polymoog 203A Restoration - You Got to Love Spaghetti!!

[HideawayStudio]

Not new to to these beasts but there is so much wrong with this example I've decided to blitz this restoration and tear the whole thing down to nothing but a huge wiring harness and a pile of pcbs..

Worth it though - its complete, almost entirely original/unbotched and remarkably free of corrosion.

A h**l of a lot of work though and not for the faint of heart.

Can you guess what it is?





It's one of three major restorations due this year...

This is just the front panel assembly.. a sea of connectors and colored wire - very thankfully with reference designators on each but rather bizarrely not with pin 1 positions marked.

Now with a new set of LEDs and around 25 new 4007 transistor arrays - both notorious for failure on these beasts (yes, even the LEDs fail!.. something that is rarely seen with modern LEDs.)...

[HideawayStudio]

I ditched the download and posted the pics directly..

Having reassembled the whole front panel assembly this evening after replacing all of the LEDs, CD4007 transistor arrays, CMOS MUX and Op Amps in the resistor pack drivers and audio reference voltage rail (Vch) I managed to test most of the front panel functionality on the bench in isolation. All seems to be ok.

The pcbs within the front panel are a bit of a sod to get to to say the least which is why I have taken such a drastic route with component replacement in this case.

[Cybercardinal]

Sweet jesus that's a lot of work. I have one with a list of 10 faults or so. Wish I could send it over to your. Way to expensive and troublesome though.

Would you happen to know where I can get the male part of these connectors?

[desmond]

You keep getting these doozy jobs, Dan!

What's next after this one I wonder - complete CS80 rebuild..(!)

[sam]

I noticed a few with blue LEDs....are you staying original..?

[HideawayStudio]

You keep getting these doozy jobs, Dan!

What's next after this one I wonder - complete CS80 rebuild..(!)

A Late 1940s Ondioline next...

[HideawayStudio]

I noticed a few with blue LEDs....are you staying original..?

I'm not sure blue look right on a 1977 Polymoog. The original 5mm LEDs are unusually squat in the Polymoog so most, including myself, fit 3mm LEDs in their place. In this case I've decided to go with just red but the last one I restored I fitted red, amber and green LEDs for each block of functions which was quite pretty.

[HideawayStudio]

Sweet jesus that's a lot of work. I have one with a list of 10 faults or so. Wish I could send it over to your. Way to expensive and troublesome though.

Would you happen to know where I can get the male part of these connectors?

CORRECTION:

These are 0.15" (3.81mm) pitch connectors. The original series is obsolete but there is at least one more modern series of pin header that can be used as a replacement with a compatible mating body. Unfortunately it looks like these are now end of life too.

This pin header should fit the original footprint: (still in stock)

http://www.digikey.co.uk/product-detail ... ND/2273451

Sadly it looks like Digikey no longer stock the mating half which looks like this but in 0.15" pitch:

http://www.digikey.co.uk/product-detail ... ND/1136248

My biggest gripe with these in the Polymoog is that in almost all cases they didn't use polarised versions so its really easy to make a mistake and plug them in backwards.

TIP:

If you accidentally break a single pin on one of these headers it is possible to remove it by heating the pin at the bottom of the plastic base with a soldering iron and carefully extracting it with a pair of pliers. A suitably long pin from a 0.1" KK series header should fit in its place.

[Automatic Gainsay]

LOOK WHAT DAVE LUCE DID TO YOU

[Dr. Phibes]

It's odd how they socketed some chips but not others.

[ppg_wavecomputer]

[...] What's next after this one I wonder - complete CS80 rebuild..(!)

I'll have some voiceboards, please.

Stephen

[HideawayStudio]

LOOK WHAT DAVE LUCE DID TO YOU

Many of Dave's designs were very clever and I think he was perhaps given a hard time for them being a little too convoluted and complex but that said there was definitely a slight lack of common sense from time to time! - like a mad professor

His patented carrier wave based keying method on the Taurus and several other models was very clever. It AC coupled a 20KHz tone to the pitch CV resistor ladder so that both a pitch CV and a demodulated gate could be derived from just a single set of keyboard contacts.

The PLL controlled twin divide down ranks with beat control in the Polymoog is very clever too and makes it quite a lot more capable and characterful than many more basic divide down synths. Although the velocity sensing has some pretty basic flaws (like having to be "pumped up" for the first few seconds of playing!) it adds SO much dimension to the instrument - it really is a joy to play in this respect especially with a new set of bushings fitted to the semi weighted keyboard.

[HideawayStudio]

It's odd how they socketed some chips but not others.

Actually this is quite normal in gear of this age and quite telling too...

Moog very sensibly fitted all of the 4000 series multiplexor ICs and CD4007 transistor arrays and CA3080 OTAs in sockets.

..interestingly though - the frequency MM5823 divider chips are not in sockets!

So it seems even when they were new those early CMOS MUX were considered likely to fail.

You will find many other synths and outboard of the era have the same thing.

Shame they didn't socket the dual op amps though!!... I worked on a Polymoog a few years back where the op amps were failing on literally a daily basis after a very long time in storage. After replacing lord knows how many of them over several days the whole thing settled down and has been fine ever since.

[synthroom]

It's odd how they socketed some chips but not others.

Check out an Emulator II some time - there's like 175 chips in sockets on them.

[Dr. Phibes]

You will find many other synths and outboard of the era have the same thing.

Indeed I have. I guessed it had something to do with their perceived reliability, I just wish they were more... consistent. Seems like when I'm fault finding it's always the chip that isn't socketed

Check out an Emulator II some time - there's like 175 chips in sockets on them.

I've recently been fixing up a Crumar Trilogy and every single chip is in its own little socket; it doesn't half make life easier, although there's not quite that many.