GE microwave
All runs, but no heating.

I am writing this while trouble shooting.

I just measured the voltage on the Mag Xfmr Blue and Red wires, 120V with oven not running, (coming back through the transformer) these are supposed to go low (ground) when the Relays close to connect these wires to neutral. Mag is running, here is the key, they go low for less than a second, then go high again, like the relays close, then re-open right away.
So, it appears the Board with the relays is not keeping the relays closed, I get that, but why? Both relays do go closed for a almost a second, but open back up.
The troubleshooting guide suggests a new PCB, but I am wondering, where does the "gas sensor" the 4 wire sensor on the exhaust duct come in? It connects directly to the PCB, could it be bad, not allowing the relays to remain closed and the Mag to run.

Thank you for any thoughts or advice.
Rob

Any ideas??