[flyingtech55]

Here's my 2p worth. Put the height and linearity controls in the (physical) centre of their travel. See how much height you have and what the linearity is like. This may give a clue. Go through all the components in the chain R144, R145, R146, R147, R148, R150 and R151 and check that they all intact and that the values are accurate. Sometimes the carbon controls can drift dramatically. If you short R170 it will clear the thermistor.

Have you tried 'scoping the waveforms?

Good luck

TimR