I found a great price on a KORG polysix but it needs some repairs. The seller has this to say about it:
“Vintage korg polysix analog synth in excellent condition. There are about 15 keys that do not connect or are only making proper contact some of the time. Some will work if you push them extra hard. Buyer will need to have that issue serviced by a proper tech. All synth functions work and operate as they should. Overall, this synth is great aside from the select troubled keys.”
It seems like it may be an easy fix. Do you guys sell any thoughts on this? Does syntaur sell any replacement products for the polysix? Could this be as easy as cleaning the contacts?
The main issue to watch for on a Polysix is damage to the circuit board(s) from a leaky battery. If it is working correctly, that’s a good sign - but once there is battery leakage, it can slowly corrode the PCB traces. So it may work fine now, but not in six months. I don’t want to be a nay-sayer - it’s certainly possible that the board could be undamaged, or it could have been damaged and then repaired, which is also fine. It’s a good question for the seller: Was there ever battery damage?
I’m gonna say that the key issue is likely very easily fixed. You might want to disassemble the keybed, and wash the contact strips in warm water with dish soap. Or you can slice up a Cap’n Crunch box, and likely get it fixed pretty easily: https://syntaur.com/DIYdocs/DIY0017.html
I just finished to restore completely mine this summer including keyboard. I really love this synth but sadly the keyboard is not the best designed part. First the keys are flimsy, very “light” in touch and have an horrible springy sound when released. To have an access to the rubbers you’ll have to remove an incredible number of screws, take a lot of care with the plastic retainers/spacers that hold the pcb (they always want to jump and hide somewhere). At this stage … this is yet a lot of work so my advice is : go for complete restoration. I mean all the rubber have a thin carbon disc that makes the contact with the pcb that is more or less aged depending on use and the octaves. If they fail to make contact with the pcb even after cleaning with isopropyl alcohol (and lot of mine did) you’ll have to replace the whole raw of contacts and of course they are not all the same ! When i did mine no rubber strip was available at syntaur (i needed also some for a sixtrak that shares the same keyboard) so i went for the cheapest (and time consuming !) solution, i bought hundreds of thin carbon disks used to repair remote controllers and that have the exact same radius, and simply glued them on the existing disks with a very thin layer of glue. Then i bought a steel metal bar that i cutted in 3.5 cm strips that i glued under each key (beware with the black keys to not place them in the travel of the key guide before gluing !) . Then finally i took some thick natural wool and put a little piece thru each of the springs with a needle (always use a natural wool, felt, or subtance here because synthetic stuff will badly decay with time). Before putting all keys back again i reinstalled the rubbers and pcb on the key bed and connect it to the synth to verify that all keys are playing by just gently touching the top of the rubbers. If all is ok it’s time for final assembly !.
The bushings (rubber parts restraining side movement of the keys) are prone to crackle and retract causing bad playing sensation and clacky flimsy keys. If the part is unobtainable i take cheap thermo retractible rubber tubes used in electronics and add a layer on the existing ones verifying that the key is still moving freely and more than one layer if the old bushing is gone. I add a little dot of silicon grease at this place when installing the keys back (always the black keys first !). At this time you can control and adjust the level of each reassembled key with a plier if necessary by pulling up or down the corresponding bushing on the keybed. All of this will take you more or less 2 hours but the final result is just awesome ! the keyboard is now very comfortable with the weight added, much more precise due to the new bushings and totally silent (no more ringy noise at the end !) … forever !
My special advice for this synth if job has to be done around PSU and CPU board (common issue) … install a kiwisix kit . I did it for mine and i have now hundreds of presets, total midi implementation and a much greater global use for live performances.