After I finished actually working on this Juno, I finally caved in to my perverse scientific curiosity and decided to see if I could use parts from a few half-failed Juno chips (ones from various Juno 106s I’ve worked on, that weren’t fully restored by the soaking/stripping process) to create some fully-functioning ones.
Sometimes you can tell that only a specific part of the voice chip circuit is bad (resonance doesn’t work right, VCA doesn’t work right, etc). I usually just pop in a clone at that point because they don’t cost that much and the time I already spent picking at it is a sunk cost. But I have the internal schematic for the 80017A voice chip and it shows which of the SMD chips is responsible for each of these. It should be possible to mix and match them to make a good one. The hard part of the process is just how cheap and delicate the PCBS are. The traces are just ceramic and once the solder comes off one of them for whatever reason, you’ll never get it to stick again. Soldering SMD is just fine but desoldering is another matter, and I couldn’t desolder things normally because of the need to make sure some solder remained on the pads.
So… as it turned out, just as I had pretty much known ahead of time, the process was really stupid and annoying and in my opinion, not worth the trouble. But because of my personality I had to try it at least once, just so I wouldn’t have to wonder any more.
YES, basically I did this in what would have otherwise been my “free time” just for “fun” and the possibility of ending up with something that was worth $43.
Next time I’m looking to have fun I should just do what I normally do and build one of my synths a new power supply.
Work done: the usual. Also, fixed a little bit of damage on the module board that was causing one of the voices not to work even with a good card in the slot.