Does it have the infamous battery damage? A blinking speed LED indicates that the key assigner circuit is probably working (which also means that the four key mode buttons should theoretically work). If all the other lights in the programmer section are lit it hints at a problem with the processor board (KLM367). There is an active Polysix yahoo group which I suggest subscribing to.
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Re: [vintagesynthrepair] Restoring a Korg Polysix
2011-11-06 by Malte Rogacki