Korg polysix is a really nice keyboard ,but over the years a lot of them got damaged in the battery board area. the internal memory battery leaks and eats the board traces and chips away. this happens especially when the synth is being stored and not being played for years.
i always assumed that the battery damage on a Korg Polysix is a hard and a time consuming fix but.. doable. this was after i fixed a similar problem on a bigger Korg trident battery circuit. i was wrong again. this Polysix repair was HELL and it's not over yet.
i always wanted to own a Polysix since my favorite synth is the Juno-60 which was at the time the equivalent synth (some will say more or less) from the rival Japanese company ROLAND.
i found this "NOT WORKING" Polysix in a reasonable price on eBay and decided to buy and fix it . the seller posted some pictures of the damage and i thought that I've seen worse ones before.
but when it arrived i discovered that the synth was stored in a humid environment (corrosion all over the metal parts), and was standing vertically on one side, probably for years, so the battery acid took it's time and crawled from the (top) side down toward the other voice board. yes, the one with all the rare and discontinued ssm2044 (Filters) and ssm2056 (EG) chips. i didn't get there yet. i'm still working on KLM-367, the infamous battery board. it was eaten by acid- in some areas on both of it's sides.
i took the time to rebuild all the traces, put a new battery with a new holder,replacing few chips etc. and when i finally got it done i found out the there is only one key on the keyboard that can make sound. probably there is a problem in the key assigner circuit as well. i also found out that someone tried to mess around with those tuning trimmers on the voice board so the sound is changing on each press on that single note.
and then i found that the big socket (for the programmer processor) was rotten from the inside the it's contacts were kinda intermittent.i needed to break it out little by little, ( in order to save the order all the small connections i soldered underneath) and then to clean everything and place a new socket instead. (see the picture). one hell of a machine it is! ...there is still so much to do , i hope it'll worth it finally...