So what are the common reliability issues and how easy are they to fix? I thought it best if this section was written by the technician who is restoring my Polymoog 280a. Hearing it from "someone who knows" seems the best way to approach the subject so over to you Colin...










You could be forgiven for assuming that the Polymoog is a nightmare to own. This is partly because of its early reputation and also because nearly all second-hand Polymoog's are inevitably sold with some kind of fault. These vary from simple power supply problems to total non-working units. A prospective buyer should put this into perspective. The majority of the machines that are still around today are now entering their third decade. A Polymoog that does come up for sale may have been stored unused in a loft or garage for 10 to15 years before they are sold, so some investment in restoring them would seem inevitable. A buyer should also be aware that because of the shortage of certain parts, on rare occasions some Polymoog's that are sold as "non-working" may have been stripped to keep another machine running so always check carefully before parting with any cash.

As far as reliability is concerned, most Polymoog's that have survived into this millennium can be made as reliable as any other analogue synth of their vintage. Most, (if not all) have had some or all of the factory reliability updates added along the way and these have addressed all of the issues that came to light during early production. Any mod's that haven't been carried out can easily be added by a competent tech in an hour or so.






Polymoog owners & service manuals














Common Faults. There are a few which crop up regularly and in particular, the single most common fault found on a Polymoog is the Modulator Card connections. Each card sits in a slot, (similar to a PCI slot on your computer). It is quite common for a "dead key" to be just a poorly seated Mod card. You can save yourself a lot of time and money by simply taking it out and re seating it. Any roadie that hauled a Polymoog around on tour in the late seventies/early eighties knows that one, as cards do have a tendency to pop out when the unit is moved.

Most other problems involve the Integrated Circuits (IC's). A Polymoog uses an abundance of them and all IC's have a certain life expectancy. This is based on their substrate, heat and workload. Substrate is the insulation between the internal components on the IC. Early IC's as used on the Polymoog had a substrate (insulation) thickness of 0.25 microns which inevitably breaks down with time and heat. Modern IC's use a 0.5 micron substrate and are likely to out live their owners. This doesn't mean that all the IC's should be replaced or are about to spontaneously combust, but a few failures are inevitable over a lifetime.

The Polymoog has 2 divider IC's (MM5823) associated with each key. Each divider services 6 notes for either pulse or sawtooth waves. If you find "dead notes" on certain presets or a continuous sustain then it is most likely that this is the cause. It is also quite common for the same note across several octaves to be affected. There are also Ca3080 and Ca3130 IC's associated with the VCA's and Reference Oscillators which are another common failure. Usually, the symptoms are that the Beat LED is permanently lit, (no pulsing) and the loss of a tone source or modulation. Another very common IC is the CMOS 4007, 4051, 4016. Most of these are for switching tasks. Common symptoms are dead controls, buttons or presets.






Fine tuning on the production line (1977)


















Another common fault is the keyboard itself. If the synthesizer has been in a dirty environment, key triggering can become a problem. Poor key alignment and a "clonky action" are a sign of a tired set of bushes. Repairing the keyboard itself is very fiddly and is best left to a tech in my opinion, unless you know what you are doing. Once it has been re-aligned and new bushes fitted however, the keyboard action on a Polymoog can be superb.

There are also some things you can do to help your Polymoog out where reliability is concerned. If you own a 203a, it's a very good idea to replace the LED's and load resistors for new ones. Modern LED's use much less power and you will be giving the already hard pressed power supply unit (PSU) a break. If your Polymoog has seen a lot of action you might also be wise to replace the capacitors on the PSU as well. This will help reduce the load and prevent ripple on the output. If you're still confident and would like to take it a step further, you can also consider replacing every Op Amp and CMOS IC - they cost very little!

Possibly the most comprehensive refit has been carried out by Kevin Lightner, (a top tech in the US). He has re-soldered all 4000 joints and replaced every capacitor during a full rebuild but you will need deep pockets as the amount of hours spent can be up to 3 weeks solid work!

These faults are what you might expect to find on a second-hand purchase or faulty Polymoog. I wouldn't consider these to be everyday occurrences, because they are not. My studio Polymoog's have remained fault free for 2 years now. I just wouldn't recommend that you gig with the old lady these days, a studio environment is far more dignified and should allow the Polymoog to remain trouble free if it's kept cool, clean and not moved with excessive force.




MainBoard assembly, Cheektowaga (1977)