Sharp R1830 Microwave/Convection oven

[BobE]

This is an 18 year old oven in a motorhome. A year ago we had a voltage spike in a campground that took out a VCR, DVD player, the Sharp microwave and a 2000 watt inverter. I managed to find a control board for the microwave which brought it back to life and I thought it was completely repaired but lately the unit will trip the 20 amp breaker for the circuit it is on but only when operating on convection. The heating element still works as the oven is being heated up until the breaker trips. The only other symptom is that sometimes I see sparks inside the oven cavity while it is operating on convection. These are similar to sparks when the carousel tray or racks are off center and make contact with the walls of the cavity during microwave operation. However, this is not supposed to happen during convection operation, is it? Do I have a short somewhere or could the convection heating element be bad somehow even though it is still heating?

 

[Tha fios agaibh]

Could be a number of things. The voltage spike may have damaged insulation and its shorting out somewhere when it heats up.

The circulation fan used for convection may be shorted out. You could try to unwire it temporarily to see if problem goes away.

I would try to discern exactly where sparks are comming from.

If you still can't find the fault, its probably time to pony up for another microwave.

 

[Bluejets]

Heating elements are made up of a steel tube with manganese dioxide compressed powder as an insulator and the element suspended inside.
With continual heat cool cycles the outer sheath developes small cracks into which moisture gets sucked in when cooling. The insulator is highly absorbent and this gives rise to tripping any safety switches.
If you do sometimes manage to get it heating the heat forces the moisture out again but a track starts to develope and eventually the element will begin to break down to earth or just simply begin to eat away at the element material causing a blow point in the continuity hence the sparks.