Normally you'd expect an old synthesizer to have problems, for example scratchy pots, dead voices, leaking batteries and dead keys.
Well, the Poly 61 was completely silent when I got it. It lit up and I could edit the presets and store them and everything, but there was just no sound anywhere. Also, I saw the leaking battery.
I was expecting a lot of hopeless searching for errors but I was pleasantly surprised...
I decided to power the thing up again and see if there really was no sound in it, and sure enough, I could hear a note being played from ONE of the keys on the entire keyboard. Wow, 1 out of 61 is quite bad. Anyway, this sort of calmed me down since I was afraid I was dealing with some sort of dead assigner for the voices or something major, but now I was hoping that all the problems were due to the keyboard rubber contacts needing some attention.
I removed the keyboard, disassembled it completely, gave the keys a bath, cleaned the rubber contacts a bit with rubbing alcohol and then rubbed them some more with cotton q-tips or whatever they're called (the things you can clean your ears with). I connected the keyboard before putting all the keys back just to test the rubber contacts and I was actually able to trigger a note from every key! I could also see that the every voice was working because there's a small LED for each voice that lights up when it's in use. Lovely!
So, I put the keys back and attached the whole keybed to the synthesizer and tried it. For some reason almost the entire top octave was not working and a couple of other keys worked only sometimes. Anyway, I now know that the problem was all keyboard related and not electronic.
I will let the keyboard stay like this for now as I would otherwise have to take the whole thing apart again and clean the rubber contacts more.
I DID measure the resistance when the contacts were pressed and I am pretty sure that every contact gave less than 500 ohms resistance. I think that should be enough but I could be wrong.
What about the battery?
Yeah, well. At the same time as I had the unit open I removed the CPU board with the leaking battery on it. I was wondering if I should cut the battery off first and then desolder it but I decided just to desolder it straight away and had no problem at all.
I then used rubbing alcohol, some pieces of cloth from an old pillow cover and a small paintbrush with stiff bristles to try to clean up around the battery area.
I still don't know what to replace the battery with: A new 3.6V NiMH battery or a small 3V Lithium cell that needs a diode as well to prevent charging.
I think I'll get a small NiMH battery pack as it doesn't require any diode and it's the same voltage. However, to make installation easier next time I soldered to wires to where the battery had been so I can install a new battery without having to remove the board next time.
So, this is what it looks like at the moment:
Camera flashes have a tendency to reveal things. I remove some of that dust on the left side of the board after seeing this photo...
I saw some corrosion on some places but since everything was still working I decided to just scrape off the worst visible crumbly stuff and clean as well as I could with rubbing alcohol.
Headphone volume and broken line out connector
I had noticed that the volume in the headphones jumped up and down and sounded bad when I moved some wires around. Bad connection somewhere? So, the last thing I did was to check the connector board. One solder joint was broken on the line-out socket so I fixed that. Also, I noticed that one of the pins on a connetor apparently was a bit loose since I could wiggle it in and out of the connetor a bit, causing the volume in the headphones to drop considerably.
It didn't seem to affect the line out volume though so I just left it. At least I now know what the problem is and I guess I can replace the connector or just attach the wires permanently to the board instead since the other end of the cable has a connector too so I can still separate them.
Oh, there are still problems with the buttons on the panel. I mean some barely respond, some "double click" and some barely respond AND double click. I'm not going to bother with those at the moment because of what I just realized. See below...
What? I knew it had no MIDI, but no CV/Gate either?
OK, I feel really stupid. When I bought this thing I got it for about 100 Euro, convinced by the seller that the problem was something simple. I knew it didn't have MIDI but I just ASSUMED that the Polysix had a CV/Gate interface and that the Poly 61 would have one too. Turns out neither of them have CV/Gate :)
Well... While repairing it I noticed that the ONLY real interface was a trigger input for the arpeggiator. Duh? How useful is that? Not that I have ANY way to currently control a synthesizer using CV/Gate but hey, I could always get a converter or something.
I bet a MIDI retrofit kit for this thing would cost more than twice as much as I paid for it. The Poly 61 is not really good enough to motivate investing in a MIDI retrofit kit. I guess they're difficult to find anyway since the Poly 61M also exists (M for MIDI) so why bother?
I know Korg sold them for the vanilla Poly 61 after they released the 61M but that was long ago :)
But, well... I guess I could always try to make my own MIDI interface for it... In another century or so when I'm done with my other projects :)
Anyway, I decided that I've had enough of this synthesizer for now. It sounds quite nice and a bit fatter than I expected it to, but the absence of any useful interface made me lose interest in it so I'm not going to bother fixing the small annoyances that remain. I know at least that the synthesizer part of it is working and I guess that's the most important thing...
If you have a cheap MIDI-retrofit kit or schematics for one, please let me know! :)