Moog Polymoog 203a restoration thread.

[hfinn]

Well I'm about to undertake a Polymoog 203a restoration. This one is serial number 3999 so I estimate this to be one of the last 100 that were made which will be great since it will most likely have all the modifications that were don throughout production. This one has a bunch of issues, but should be restorable since nothing is terribly major, just A LOT of little things. I hope to update this thread with developments as I work though it. First up is basic fault finding and this week will be a disassembly which will allow me to redo the bushings (and get rid of that black piece of electrical tape holding middle C down...)

I'm also hoping to find a 280a for sale locally too as I want to have a pair.

Here are some pictures of it before I do anything to it:

[Z]

Cool! Keep us updated.

I picked up a 203A late 2009 with only a few issues. I'll be taking it to my tech soon (they've already got a few of my synths right now - don't want to overload them)

[rjd2]

man, refurbing one of those SUCKED. good luck.

i can give you some heads ups on some things if you want.

[hfinn]

Yesterday I received the huge service manual in the mail with all the foldouts and ordered some parts that I know I will need for it. Tomorrow I will get the 71 bushings I will be using for the keyboard.

Thanks rjd2, I might have some questions as I go.

[dr funk]

I have a fully functional 203a here (serviced by James Walker in the UK), so if I can help, feel free to ask!

Cheers
Frank

[madtheory]

Great idea! Thanks for sharing. Good luck with it.

What type are all those square white caps? They look like the long life type.

[hfinn]

Well it's about 60% dissassembled. Thought some might like to see what it looks like with the front control panel off and keybed removed. When I reassemble it I will make sure that screw standoff's are even at the same height... I have some other things to sort out like one of the tabs that a key bushing sits on was snapped off.

Planning on replacing all PSU caps, 24 divider chips with sockets added for ease, Both UA726's, opamps, all 38 LED's with lower power smaller ones, and lots of CMOS chips. I'm hoping that when I'm done and it's back together I will have one of the most reliable 203a polymoog's out there. Now to find a 280a...

[shaun]

Hi there,

I wish you could luck with this one.
I have one sitting here for more than a year now which has probably been stuffed with all defective boards from other Polymoogs in some workshop.
So far I've replaced more than 10 Polycom Boards with dead polycom chips. The balancer boards had 5 out of 6 LM358 (!) dead. Several LEDs where dark, the 7 Segment as well. One of the 1458 buffer amplifiers on the mainboards was gone and the whole power supply was destroyed by some idiot who bolted the regulators to the heatsink without mica washers. The rectifiers and the transformer blew up, as well as the 16V Transil.
It has two toroids now and a completely rebuilt power supply. Three octave dividers where dead which have been replaced with the perfect little boards I bought from some guy in UK for a very, very fair price (when it comes to TOS chips like the 50240 and similar I have developped my own universal TOS module which also allows for special tunings like well tempered and so on and improves the frequency precision on demand).

I think it's not done by just replacing the CMOS chips, actually I left them there because faults in logic circuits are easy to find, they tend to be somewhat logic
It makes me much more nervous that 1458 and 358 fail, as they are spread all over the instrument. Now I have to work on the filter section and it will be done for now.

regards
Stefan

[minime123]

polymoogs can be a serious pain to work on, but theyre great once youve finally got them fully functional. good luck, heath!
mini

[masyst]

That seems to be a nice little project :p
Do the Polymoogs sound nice? Been curious about them since when I heard that Richard Tandy used one in ELO...

[dr funk]

This my be of interest: Famous Polymoogs

Frank

[LWG]

This my be of interest: Famous Polymoogs

Frank

Hello,

Pretty good page, although a number of noteables don't appear on that list. Keyboardist/guitarist, David Sancious
was a major user of the Polymoog in the late 70's

Here, he toured with bassist, Jack Bruce and used one on the road:

Jack Bruce - "Bird Alone"



He also recorded with the Polymoog extensively on his own solo releases, which prior to 1980, inluded a
Minimoog and a rev2 Prophet 5:

David Sancious - "Valley Of The Shadow" (1979)




David Sancious and Tone - "Prelude #3" (1978)




The Polymoog is also used by him on his recorded version of, "The Bridge", classical piano compositions
with synth overdubs, which also include Minimoog and P5.

Other noteables who used the Polymoog was Dexter Wansel, producer/keyboardist with Philly International
records during the 70's, and Brian Jackson from the Gil Scott-Heron band.


Regards,


-L

[hfinn]

Well, I pretty much disassembled the whole thing and put it back together again. No new parts are in it yet and a good chunk of the problems it had are already gone. I still have an issue with the rectangle wave in "Free" mode not following fine tune or pitch ribbon, Most all of my noise issues are gone though. I'm planning on buying a complete set of the newly remade divider chips from flatkeys and installing all new ones.

I CLEARLY have an LFO issue. The "Shape/mod" section isnt working right.

Good news:

-Resonator section works 100% although I want a new three way selector switch for the low/band/high as this one is noisy as h**l and cleaning it really didn't help.

-VCF section works 100% (just needs a calibration)

-Loudness Contour section appears to be 100%

[ZeeOne]

That's a cool synth you've got there...everytime I see a PolyMoog, I get reminded of the video for Gary Numan's "Cars"...

Fast forward to 2:49 to see what I mean...

[hfinn]

I'd argue to say that when I'm done with this one it will be probably one of the most reliable, functional polymoogs in existence. I'm pretty much replacing every CMOS chip, op amp. 18 CA3080's, 24 dividers, 2 UA726's, 38 LED's (lower current ones to take some strain off the PSU as well) in it as well as rebuilding the PSU with modern day components. Full set of new keyboard bushings as well.

In talking to Chris Burrell who is producing modern divider chips he also told me this which will be interesting:

"We will be introducing our MK50240 replacement soon, the top octave synthesizer chips. Our replacement has 12 "real" synthesizers which produce outputs that are either a) Original MK50240 divisions ratios (slightly out of tune) b) precise equal temperament (to within 10 millihertz), c) Pythagorean or d) just. These are selectable via a rotary switch which can be panel mounted. There is also a rotary switch to transpose key! Again panel mounted."

Yesterday fixed one of my LFO issues with the saw wave, now I just need to adjust the Rectangle wave.