Frigidaire Oven Problem

Hopefully someone can help me diagnose this -
Frigidaire FEB798ccbh electric oven (double). Bottom oven works fine, top oven shuts off after setting temp, display just turns off. Occasionally will work, if you try it enough times. Discovered disconnected oven vent when unit was opened - Sure the excess moisture caused or worstened the issue. Tried "rebooting" the oven with no success.
I'm guessing it's either the transformer relay board or the ECU, any way to rule one or the other out?
I'm fairly handy with a DVM, so specific troubleshooting steps would be most appreciated
Thanks for any help and happy holidays!

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