GE 24 inch Wall Oven / Microwave unit.

A few years ago a electrical surge took out the oven control board. Replaced the control board assembly, but not the power supply assemble piggy backed onto the control board. Tried a self clean and received a F2 error code. Replaced the temperature sensor twice and that did not fix it. fas forward a couple of years, now I need to self clean instead of manually cleaning (bad knees) and I need to fix it
Things I have checked:
1. Oven works fine in normal bake and broiled mode.
2. Oven fails on F2 error code 20 minutes into self clean cycle. Oven did get hot enough to burn some of the deposits to ash.
3. There is a fan located between the microwave and oven. It blows air across the top of the ovens outer shell where the lock motor and what appears to be limit sensors are located. This fan does turn on during self clean. I cannot verify it is turning fast enough, but there is a very faint breeze coming out of the vents between the microwave and oven. Just enough to barely move a kleenex. There is no dust screen on either side of the fan or in any of the sheet metal channels that directs air flow to it.
4. At room temperature, temperature probe reads i6 ohms (part number WB21X158). When the error occurs the probe is reading 75 ohms.
5. Visually inspected control board and power transformer board. No signs of damage or overheating, no smell of magical smoke. :)
6. Inspected and verified all connectors are clean and tight.
7. Left the control board hanging out of the oven (its designed to swing out on a hinge). Placed a 12 inch fan in front of the unit on high, Directing the air over the control board and into the cavity the oven fan blows into.

Any suggestions? I can't afford at this time to buy a new unit, plus this has now become personal... :)

IS there a limit switch that should be opening to cut power at high temp during the cleaning cycle?