[WaveyDipole]

Then there must be another explanation for that very low voltage reading across R310/C311. Assuming that your probes made good contact, then such a low voltage would indicate to all intents and purposes a short or at least a very low resistance under running conditions. Back in post #40 wme_bill mentioned that resistors can sometimes change value under high voltage stress conditions. Maybe R310 is OK when examined using a low test voltage, but breaking down under running conditions where much higher voltages are present. I would suggest replacing that resistor.