I bought this Korg Poly-61 as “for parts or repair”, it basically did not work at all. From the description of the Ebay listing I suspected that it had a battery leak. These old NiCad batteries can do quite a lot of damage as it eats the copper away in the traces in the board and it can also damage components. The patch memory of the unit will most likely be corrupt and there will be damage around the battery.
Note that it is possible to buy newly made boards and this is probably the easier option especially if you do not have the tools and/or time. I enjoy a bit if troubleshooting so I decided that I would give a manual repair a try and I could not really do more damage to the unit as is was already in such bad shape.
I have done this procedure on a Korg Polysix a couple of years ago following Old Crow’s Polysix Guide. The board in the Korg Poly-61 (KLM-475) is pretty similar so it is applicable here also. This is very time consuming; I suspect this took 10-12hrs of combined time for me. This will most likely not work on the first attempt and you will need to go back and forth. The damage will vary between different units depending on how much it has leaked etc.
Basically you will need to:
- Remove the old NiCad battery and recycle it safely
- Clean the board and inspect the damage (I used isopropanol, distilled water and a toothbrush)
- Mark all traces that have damage on a printout of the schematic from the service manual
- Remove ALL traces which have black spots on them or have other visible damage
- Possibly drill out the via holes of the affected components. I did not do this as I do not have drill press and I think I would just do more damage with the Dremel if I do it by hand
- Manually patch the traces by soldering wires (it is now that you are glad you have marked traces on your printout!)
- Mount a CR2032 battery holder, remove C29 and replace R70 with a diode
- Restore the factory patches (or create patches manually) via the tape interface
In my case I also had to rebuild the cable loom from the main board to the voice board as the corrosion had eaten away the crimp terminals in the cable even on the voice board side. The patches are not that beautiful, but it works and they are hidden on the underside of the board 🙂