Polysix - No saw wave when warm

Hello, I am having an intermittent issues where I lose the sawtooth wave on all voices - setting the knob to saw just gives a pulse wave instead. At the same time, the sub osc will get stuck on at 2 octave when the switch is set to off. For the most part, this seems to be related to heat - I can turn the synth off until the back panel is cool and it will return to normal function.
The battery was replaced by the previous owner and there is no visible damage that I can see. Thanks for any tips of where to look.

The problem is not where to look, but look everywhere. This sounds like a dry solder joint. This is an early failure symptom that much more is to come. Take a magnifying glass or microscope and go around the all circuit boards, connectors, power supply, pots, sliders, and do the best job you can at re-soldering using 60/40 solder everything that looks dry, cracked, or has missing or evaporated solder connections.

This happens to all electronics eventually so its nothing to panic over. As said do the best soldering job you can because of it doesn’t work and you end up taking the unit to another tech, you don’t want him fixing bad soldering too.