Wow, so many questions
torinkrell wrote:I understand that the Memorymoog offers one of the biggest challenges in synth maintenance today.
While citing the Memorymoog, any analog polyphonic or analog with digital patch storage is a challenge as they are complex machines.
What other synths are similarly challenging to repair and keep running?
Repair-wise I'd say the worse ones are those with point-to-point "spaghetti" wiring such as the old Yamaha CS-80/60/50. Everybody has varying experiences on which vintage gear is easier to keep running, there doesn't seem to be a solid consensus.
Which use failure prone rare parts
Failure prone are those with early generation tantalum caps before 1982 (not every synth used them). Sometimes poor design can contribute to part failure downstream - I was never impressed by power supplies in ARPs, and SCI pushed their power supply current capacity too close to the maximum in their P5s.
Frankly every vintage synth has some rare parts in the form of switches, pots, ICs. I am not fond of anything with slidepots as they can be difficult to find in low quantities 20 years down the road and finding an exact physical fit can be a real problem (mm travel, footprint, etc). Board-mounted pots and switches pose a challenge - I have a Barbetta keyboard amp with bad pots and replacements that fit the PC board holes are nowhere to be found, had to shoehorn trimpots in place of them.
and which use parts that will be easy to find even in the future?
Don't count on EVERY part being easy to find in the future. Through-hole components are getting harder to find as OEMs are switching over to SMT. Stuff like the CEM3340 VCO ICs are not bloody likely to be made again because the original fabrication technology is obsolete and the development costs of converting the substrate design to modern fab lines would never be recovered in such a niche market. Many people buy a dead or dying synth to scavenge for spare parts. Technology proggresses and obsolescence is a part of it, fact of life.
Some stuff like the Pro-One and ARP Quadra use a microprocessor with the OS stored on the on-board EPROM. You can't retrieve the ROM contents off these ICs. The source code was written in 1982 and no longer exists. This part can't be duplicated. Lose the microprocessor and you have a doorstop.
Which vintage analog synths are relatively easy to repair
Generally any monophonic analog with no digital patch recall
or rather reliable and can be expected to stay that way as they age further?
That is a function of how well it was cared for by former owners and/or how well it was designed. Obviously storing a synth in a damp basement or garage is not good for certain components like switches and pots. And while an Oberheim OB-X is a great sounding synth that is easy to service, the DAC circuitry has a design error that will blow the CMOS ICs under certain conditions.
I would guess that (looking through my gear) a Minimoog D, Roland Juno 60 and a Yamaha CS-5 would be examples of the latter.
Those are a good start. But don't be so paranoid over reliability of vintage gear. In the right hands they can last a long time. Proper storage and operation go a long way to reliability. Of course there are risks with buying used vintage gear because you don't know how well they were taken care of. That's the price of admission for the vintage analog club and you have to be prepared for some repair or restoration costs.