Tuesday, January 5, 2010

Poly 61 is "almost" working now

Dead keys
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! :)


  1. Hi I just want to confirm that if I remove the leaking battery from my poly-61, I just won't be able to save patchs right thats all???

  2. I won't promise anything but I am pretty sure that the only purpose of the battery is to keep the RAM powered while the unit is switched off.

  3. it might be a bit difficult tracking down one of those retrofit MIDI kits in 2010....

    had to carve a valley into my cpu board. the acid got to cn12, ic12, ic18,and everything surrounding q10 & q11. dry joints everywhere, only two that have to be repaired. Battery acid is a bad thing to get on CN12,yet the battery *is right next to it*

    you're lucky. every connection on my board in that area looks like its been covered in blue sweetarts.

  4. I actually ordered a newly released 3rd party MIDI kit for the Poly61 from CHD Elektroservis (http://www.chd-el.cz/) in Czech republic. They also sell Polysix kits so I bought one of those too.

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  6. that does make me a bit envious.

    I'm curious to know how the polysix affects your fondness of your poly-61M.

    Originally I wanted the polysix.I passed one up for 250USD because I need MIDI.

    If I had to choose again, I think I'd go with the midi-less Polysix.

  7. Actually I don't have either of them playable at the moment as I have no room. I did however order a MIDI kit for the Polysix from CHD as well when I ordered the Poly61 kit. So yes, I'd say a Polysix with MIDI would be nicer than a Poly61 :)

  8. I have a polysix that still has the original battery. no leakage at all but I know I should remove it. I'd like to set it up the way you did with the wires moving the battery pack off the board. Could you give anymore instruction on that? Do I have to take out the board to solder the wires to the bottom of it or can I just connect them to where the battery was connected, from the top? any info would be helpful... thanks

  9. @Anonymous: Ah Polysix. Was thinking Poly61, although the battery issue is the same. For starters, have you seen this http://www.oldcrows.net/~oldcrow/synth/korg/polysix/repair.html ?
    I GUESS you could solder the wires without removing the board if you're lazy, or even cut the battery off, leaving part of the legs and solder the wire to there.
    Shouldn't be too hard but it all comes down to how comfortable you are working with a soldering iron :) Usually soldering is done on the reverse side of a board, which is also what I did.

  10. Hy,

    I love my Poly61. My first hardware/analog synth. Got it for just 50€ in December 08 in "dead" condition - just cleaning the key contacts was solving the whole problem. Also exchanged battery for NiMh-pack.
    About the Arpeggio trigIN: It´s one of the most useful Interfaces to integrate the Poly61 into Studio environment as long as it has no MIDI. The trick is to get a type of Metronome Signal from a MIDI-controlable Sampler or Drumcomputer such as my Yamaha RX7 (RX5 should also work). You can grab it from the "Click"-Output. Amplify it to the trigger level (eg. AUX-CH PreAMP on a Mixer). I designed a 19" Unit containing an AMP ripped out of cheap active PC-speakers combined with the PCB of a 30€ digi-delay pedal from the bad-taste-brand called "Beh..." (for this task it`s fine) to shift the timing as the original "Click" is a bit shifted from Drum-Rythm. It is also great to generate creative arpeggio patterns as you tweak the feedback knob of delay and the Amp-Out Knob against each other.

    More infos and schematics will be released soon.


  11. Hi, found your page trying to get a solution with a problem I'm Having with my poly-61M, I got it used and seller told me I had to reload sounds cause some of them where "not there"
    I got the sound banks on WAV file, followed instructions on the manual to load from tape, got a "good" in the display and still some banks do not produce any sounds, any ideas?

    Thank you

  12. First thing you should do is open it up and check the battery area. If it looks like on mine you are in trouble as acid from leakking battery can damage circuit board traces and components. Battery has to get replaced, board has to be cleaned and repaired. Other than that it's really hard to tell but it's almost always leaking battery problems on these things.

  13. I believe this is what your looking for ...





  14. where,i can send my board to get clean?

  15. i am from canada bc i dont know who,can do that??