Tuesday, March 16, 2010

Replace Poly-61 battery with Lithium battery

Just a quick update. I made a small board out of strip board and placed a holder for the coin type Lithium batteries that are so common (CR2032). I put a schottky diode in series with it to prevent the reverse charge current.

I'll just put a photo here and then if you're interested you can read the rest of the boring details :)

First I tried a bigger battery actually but the holder I bought for it that was supposed to be able to hold it, was too shallow, so the clip sat too low where it was bent, preventing the battery to be inserted all the way. Annoying. So, that's why I used the smaller but more common CR2032 type. Lucky I bought a CR2032 holder+battery at the same time, just in case the bigger one wouldn't work for some reason...

After struggling with my useless little engraving machine (like a Dremel but wobbly and weaker, and cheaper..) I made a hole big enough to fit a screw through. I drilled a small hole in the bottom of the wooden case (yay for wooden cases!) and screwed the little battery board in place. Finally I attached the battery wires I had prepared earlier by putting a simple pin-header on them to a socket I placed on the battery card. I made it with three pins, using only the middle and one of the outer pins, so that if I put the connetor backwards I won't reverse the polarity. Of course I could still reverse it if I let one pin sit outside of the socket, but hey, it's a small safety precaution at least. I could have used one of those polarized connectors but I don't know if I had any at home and I already had wired soldered in, so.. Bah. This should be good enough.

The battery is a 3V cell but I measured the cell unloaded and it said around 3.2V (don't remember exactly) and when measuring unloaded after the schottky diode I even got about 3.07V. I hope that will be enough. Maybe I should measure the voltage when it's connected too :)

Now, all that remains to be seen is if it holds the patch memory after being powered off. If it turns out the voltage is too low I can always replace it with an NiMH battery instead I guess. At least it's easier now that I have the wires attached so I don't have to remove the CPU board.
Oh, it also remains to be seen if the battery explodes when the synthesizer is plugged in... We'll see :)
At least if it explodes it will do so away from the precious CPU board...


  1. Hello! I just bought a Korg Poly-61 Synth here in Nagano-city, Japan last weekend. Everything works great on it. I opened her up to check on the battery and noticed the original Varta 3.6v NiCad battery was in excellent condition. However, I am interested in changing the battery as soon as possible due to possible battery leakage in the future. I read your blog with great interest and would like to know how the outcome turned out. Any success? Much appreciated. - Jim

  2. Hi,
    You have a reference for schottky diode or Any reference is good ?

  3. I made some sounds and saved them and pulled the mains power cord, so it's been unplugged for a couple of weeks now.
    Plugged it back in last night and the sounds were still there. I haven't measured current consumption though, although that shouldn't be too hard if you have a good instrument, which I don't :)

    I used a BAT42 schottky diode, but if you can, get one with the lower forward voltage drop you can find when using a 3V-cell since it's already on the edge of what's tolerated by the RAM chip I guess. Of course, as low reverse current as possible too! You don't want any reverse current going into that battery...

    Please look at oldcrow's Polysix repair. It's basically the same procedure. http://www.oldcrows.net/~oldcrow/synth/korg/polysix/repair3.html
    However, the components he's mentioning are different on the Poly61 of course. I didn't remove any and I'm not sure exactly why he removed C40, but maybe it's leaking too much? R91 I guess is removed to reduce the voltage drop from the battery but I don't know to be honest.

    So, for similar changes on the Poly61 you might want to remove C29 (I think, the schematics are really crappy) and bypass R70 or replace it with the schottky diode like oldcrow did with R91 on the Polysix.
    I just left everything in place and it's working so far though so I'm not gonna change it unless the battery is drained too fast or something horrible happens :)

    Good luck!

  4. Hi there, I just bought a Poly-61 it has some issues and I found the battery was delivering just 1.6v and had also leaked fairly badly. One of the resistor networks had shorted and burst its case. So I want to faix that and replace the battery I don't want to do anything unverified so you solution looks attractive... Still working OK? So your CR2032/Schottkt Doide circuit... Can you diagram it? Words can be misleading I would like to know exactly how and where your doide is conneted! Read Old Crow's page but like you I don't want to try and transpose them to a different synth... Thanks very much, for sharing what you have!

    1. Hi! The photo at the top of the post pretty much explains it. Click on it to see it magnified.
      I just removed the battery and soldered 2 wires there instead. No modifications were done to the board.
      So it's like this:
      PCB(-) ==> black wire ==> ---Battery+++ ==> Diode--|>|--- ==> red wire ==> PCB(+)

      But, if you've had bad leakage I am worried that you may have bigger problems than just what you've seen. You may have broken traces and other damages that aren't obvious at first glance.

      I just switched it on (especially for you ;) ) and my presets were still there. So, at least the battery will last you 2.5 years :)

      Ask again if you have any more questions, and good luck!

  5. Haha I guesss when you built the circuit it looks like it does, but the connections are not shown at all they are on the underside of your little circuit

    Thanks for coming back and trying to enlighten me!

    I've read what you have written a few times and googled a bit

    I think I need to connect the negative (-) of the battery straight to the (-) of the CPU board and connect the positive (+) of the battery, first to the non striped end of the diode, then hook the stripe end of the diode to the CPU board's (+)

    Is that what you did?

    I've ordered all my bits, and I've continuity checked all my traces. All looks good. The leakage and corrosion was mostly superficial even little transistor leads are all OK, but the RA3 is deffo blown up

    I'll let you know hao I get on. BTW found another guy on gearslutz.com with exactly the same battery dilemma so I've posted a link here. You're a real gent for sharing:-D

    1. Yeah, hehe, that's what I was trying to describe with my ASCII-art-schematic ;)

      One could also replace 470ohm R70 (or whatever it is, hard to see in the service manual) with the diode, if you know which way to turn it (again, hard to tell from the service manual). I guess R70 is only used for current limiting when charging the battery, which isn't supposed to happen with the CR2032 in place anyway, so it could be replaced.
      But, I just left it and put the diode externally in series with the battery instead. Seems to work just fine, so why not :)

      Good to hear that people care for this thing even if it's a bit "cheap".

      Glad I can be of help!

  6. This comment has been removed by the author.

  7. Haha yeah it certainly is cheap but not for long I suspect

    - I had to delete my previous comment becasue I used HTML links which didn't display!

    Anyway with your help and that of 'Acriel' (who suggested similar) and 'mik-music' who you can find on Google+ All is soreted 100% grabbed my factory presets in a .Wav file here


    All loaded up and retained perfectly

    Here's my post and a couple of pics on GearSlutz:


    Pity I can't find a decent schematic anywhere:-( I have no display output but everything else is perfect now

    But massive thanks to you Peter! I owe you a pint!

    1. Hey, glad to hear you got that part of the problem sorted at least :)
      Though I bet there are more areas/components that are damaged from that leak, probably traces.

      Like I said, you could have replaced R70 with the diode instead of doing your little trick, but that was an interesting solution :)

      I actually own an original service manual (the only one I own) for the Poly-61, but if it's any comfort for you, the print is just as bad as the scanned PDFs you'll find online :(

      Keep it up though. You'll fix it sooner or later :)

  8. please help me, I was sold a poly 61 by random guy on garage clearance saying the synth works fine - it doesn't!
    I would give my right arm to play this but upon switching on here are the problems:

    - Sound is like white noise, I can just about hear the sounds up loud but there is too much distortion

    - The display numbers are scrambled

    - The chord memory and other buttons light up and work but due to the above problems it's a useless point to make

    I checked the main board and there is a slight dark brown bubbling on the tracks near the battery - so I'm suspecting it was that.
    There is a maxell 3.6v rectangle plastic battery on Velcro over a chip with the two wire soldered to the battery ports, battery dates november 2012 - I have no meter to read if its ok but i should imagine it is.

    If this is a battery leakage - and there are never fresh boards available, what can i do to repair it, where can I send it.

    any advice greatly welcomed.

    1. Hi.
      It's hard for me to say what the problem is. Sometimes people replace the battery without cleaning leaked electrolyte and fixing the damage done by previous battery electrolyte leakage. Even if it worked at the time, the electrolyte can still eat away at the traces and cause it to fail at a later time.
      Though I would say your problem is most likely due to a leaking battery, since they basically all have this problem, you should have someone take a look at it unless you're familiar with electronics and using a soldering iron, multimeter and possibly oscilloscope.

      I don't know of any replacement boards for the Poly-61. It's extremely rare to find such things. I only know there's one for the Polysix, but it won't work in the Poly-61.

      I don't know which part of the world you're in, but I guess it's not Sweden, so I can't really recommend anyone.
      You could try joining the Polysix Yahoo group and ask around there.
      Read bottom of page for subscribe address.
      Polysixes have exactly the same problem and someone who knows how to fix them would be able to fix a Poly-61.

      Sorry I can't be of more direct assistance. If you live in Sweden, feel free to ask me again, otherwise I advice you to ask in the polysix group. Good luck!


  9. Hi Peter,

    Thanks for keeping a site like this up and running.

    I have a poly 61 that hasn't been played in 20 plus years. When I plugged it in, not much happened. I opened it up and found the battery had leaked. I found your site and did the battery change out. I now have some sound, but not much.

    The program number keys don't all seem to work. Some work most of the time, some work some of the time and others seem to not work at all.

    Any ideas what I should look at next?


    1. Hey Mike,
      If your battery leaked, then there is likely some trace damage if not further component damage - did you clean up the CPU board and check for damaged component legs?
      A further danger is that the corrosion seeps to the connectors - check all the connectors to the board and make sure there's no brown or green corrosion going on there - that's probably where your problems are..
      BTW @moderator: I'm certain you want to delete "Guzzi sager"'s post - it's simply forum spam!

  10. If your battery leaked, then there is likely some trace damage if not further component damage - did you clean up the CPU board and check for damaged component legs?
    A further danger is that the corrosion seeps to the connectors - check all the connectors to the board and make sure there's no brown or green corrosion going on there - that's probably where your problems are..

  11. Jimbo,

    Thanks for the info. I'll have to open it up again and check it over. I did clean up what I could find. I'm not an electronics person but I'm pretty handy, so I try my hand at repair. It's been sitting in the attic for 20 ish years, so....I'm probably gonna end up tossing it in 20 or so more years anyway...lol.

  12. Hello Peter
    I want to copy your work pictured in the post above, and I have inte question. The old NiCad battery has two legs soldered to the PCB. I got CR2023 battery holder and a diode (1N4148..something) . Why two positive points and which do I use? can I put the diode between the postive connector on the batteryholder and the PCB (i have ni breadboard)

    Thanks for any help
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