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What you describe above it is often the result of a short in a component, the wiring or the harness.
You can check with the tech to see what he has already tested to get an idea of which way to go. It's important that the machine be exhibiting the problem when you test.
Someone needs to test the machine when the oven shuts down. We would start with the themostat/sensor for the oven (because it's related to that apparently) and then the the elements themselves. We would check that the board was receiving 120 volts when this problem was going on.
If these were found OK. Then the wiring harnesses and all the wiring to every component until we found out where the unit was shorting out.
Unfortunately, these types of problems are dificult to find and are time consumming.