Hi John,
Like sinclairtv, I did one this week where the 2 470pF 1kV diodes near the FET were shorted. Took out 2 FETs, bridge diode and fuse. Replaced all and
still no go, relays clicking on/off. Found 2 open SMD diodes and 2 open SMD resistors on the underside of the board gone.
In your board, check DP803, DP804, RP805, RP811. Schematic attached .