When my polymoog arrived, there were a few problems.
What's a "polymoog"? It's a pseudo-polyphonic analog synthesizer comprising of 71 keys. They're essentially... a glorified string synthesizer; but capable of many ambient drones, super hyperactive zinging strings, aaand, mellow due to the single filter. Some deride these as being unreliable, all I have to say is: OF COURSE something is going to have problems if it has electrolytic and tantalum capacitors from 1970 without ever being replaced
#1 tantalum capacitors were cut out of the circuit due to shorting
#2 the electrolytic capacitors are butt-ancient
#3 the previous "tech" that worked on it put nasty electrolytics in place of where actual tantalums should have been.
#4 LEDs were mismatched
The first hurdle is opening this thing, which I always dislike doing :p
I ended up tackling the power supply last, but I had a DOA diode which caused the 5v rail to be almost nonexistent. Thankfully the service manual (which is very very long and hard to read from ADD), brought me to the right spot.
Nichicon VX axials, along with vishay-sprague. Finding those capacitors is noooot fun at all. The original chemicons should never be looked at again. The terminals had corrosion: at which point the chemicon is telling you that it doesn't want to live anymore.
Upon taking a look at the reference oscillator board, you'll see a cut tantalum. Along with some Fairchild UA726HC dual-transistormahoozits. These transistormahoozits are very important. If they decide to die, sourcing genuine ones is very difficult. Most NOS ones are about $80 apiece, they will ALWAYS have gold legs if genuine.
So here's what happened after I went through all of the tantalums:
There were also other electroyltics I went through.
It's doing much better now. The only problem is that the 5v rail is at 6v and REQUIRES 6v to produce any sound. I recently found out that this is due to failing opamps. I'll go through those whenever I get time and/or feel like revisiting this thing.
Unfortunately I don't have any more board shots, I wish I took more as I went through it. Oh well. It looks very nice now, after I went through it.
What's a "polymoog"? It's a pseudo-polyphonic analog synthesizer comprising of 71 keys. They're essentially... a glorified string synthesizer; but capable of many ambient drones, super hyperactive zinging strings, aaand, mellow due to the single filter. Some deride these as being unreliable, all I have to say is: OF COURSE something is going to have problems if it has electrolytic and tantalum capacitors from 1970 without ever being replaced
#1 tantalum capacitors were cut out of the circuit due to shorting
#2 the electrolytic capacitors are butt-ancient
#3 the previous "tech" that worked on it put nasty electrolytics in place of where actual tantalums should have been.
#4 LEDs were mismatched
The first hurdle is opening this thing, which I always dislike doing :p
I ended up tackling the power supply last, but I had a DOA diode which caused the 5v rail to be almost nonexistent. Thankfully the service manual (which is very very long and hard to read from ADD), brought me to the right spot.
Nichicon VX axials, along with vishay-sprague. Finding those capacitors is noooot fun at all. The original chemicons should never be looked at again. The terminals had corrosion: at which point the chemicon is telling you that it doesn't want to live anymore.
Upon taking a look at the reference oscillator board, you'll see a cut tantalum. Along with some Fairchild UA726HC dual-transistormahoozits. These transistormahoozits are very important. If they decide to die, sourcing genuine ones is very difficult. Most NOS ones are about $80 apiece, they will ALWAYS have gold legs if genuine.
So here's what happened after I went through all of the tantalums:
There were also other electroyltics I went through.
It's doing much better now. The only problem is that the 5v rail is at 6v and REQUIRES 6v to produce any sound. I recently found out that this is due to failing opamps. I'll go through those whenever I get time and/or feel like revisiting this thing.
Unfortunately I don't have any more board shots, I wish I took more as I went through it. Oh well. It looks very nice now, after I went through it.
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