Hi,
Note: I am generally aware of Microwave internal safety and the giant capacitor risk. The manual says it has an internal shunt resistor and is designed to discharge within 30 seconds. And I know there are shock issues if working on it with mains active, and the high voltage magnetron. And issues if I were to physically change the magnetron or case position/integrity where microwaves could be emitted to the exterior at harmful levels.
I have a GE Microwave oven that shows "PF" on the display and if you try to activate it, it goes dark (light inside goes off, buttons/display do not operate) for a while until PF eventually reappears.
So after taking it apart, I see two connectors that are brown/burnt a bit, one on each of two thermal cutoffs (TCOs) (labeled as "oven/cavity" and "magnetron").
With the cord unplugged, the "oven/cavity" TCO reads open circuit and the "magnetron" TCO reads short. I'm assuming of course these TCOs are normally short and go open circuit when they exceed some temperature.
Nothing else inside has any obvious visual signs of failure. The troubleshooting flow chart on the wiring diagram says to replace the TCOs that are reading open circuit.
What could have caused this? Something causing a short in the circuit that flows through the TCOs? Fan motor failure? Turntable motor failure? High voltage transformer failure? Magnetron failure? I admit I have not yet fully internalized the wiring layout.
Photo of oven/cavity TCO:
Photo of magnetron TCO:
Photo of internals overall:
Wiring diagram:
Schematic:
Troubleshooting:
Prior history of this unit is that:
1) for years there has been some weird issue with the door interlock where either a) it thinks the door is open when it is shut, and won't activate at times without a wiggle, OR b) when the door is shut but the magnetron is off, the fan actually activate and be blowing out the back, also fixed by a wiggle. I just assume the interlock switches (there are 3) and/or their alignment with the door was bad.
2) a few months ago, the main relay that activates the magnetron failed and was stuck on. I replaced it and it has worked fine ever since. I wonder if the fusing of that relay was caused by issue #1 where the flaky switches would make/break the circuit randomly causing arcing that welded it stuck on?
Thanks