Reliability
Although built into a substantial (and heavy) chipboard case, the Polysix has some reliability problems.
Like other programmable synthesizers of the era, it had a rechargeable nickel-cadmium battery that powered the memory when the unit was switched off. The original batteries are now well past their designed lifespan and thus prone to failure, leaving the instrument unable to recall user designed patches from its memory. More seriously, if the battery is not replaced, it can leak and corrode the circuits. Unfortunately for the Polysix, this battery is mounted on the main processor board and corrosion here can be fatally damaging to the circuitry of the instrument.
Some instruments of its era had begun the move towards digital technology by using DCOs or microprocessor-generated envelopes. The Polysix, however, used a separate analog VCO, VCF and envelope generator for each voice. Whilst this might have benefits for the richness of the sound, the extra complexity also brings greater tuning problems and more possibilities for failure.
The Polysix keyboard used a light plastic keyboard with conductive rubber contacts. These contacts are often the source of 'dead' keys on the keyboard. This is probably the most common problem on old Polysix units, and one shared with some other Korg instruments that used the same keyboard, such as the Poly-61 and Mono/Poly.
The patch recall buttons also have a tendency to fail.
Read more about this topic: Korg Polysix