Making sure the yellow and blue wires from the 24VAC transformer are off the HV board, clip on a volt meter and energize the unit with the front panel switch. I should have seen voltage there for about 5 seconds as the air proving switch turned on then off, but got nothing.

Turn off the 120VAC power switch.

Per the manual, I moved back to the air proving switch, a small board with a PTC thermistor and a triac that energize to provide 120VAC to transformer. With output lead 4 disconnected, connect he volt meter between pin 1 and 4.

Energize the unit once again. Still only a few 100mV. Carefully check that there is 120VAC on the incoming posts 2 & 3, yep it's there.

Turn off the 120VAC power once again.