We see (and repair) this a lot. The problem is on the control panel, which
we regularly repair nationwide by mail for $39.95 postpaid.
This light failure often occurs when a bulb goes out and the filament
shorts, or when the bulbs are removed or installed without first
unplugging the oven from the power line. Either can cause such a
failure on the controller.
This can often also affect the exhaust fan operation, too. The lights and fan can be inoperable or stuck on too.
Details of our service and critical safety information and disassembly information is at our site, and our link is at our listing
here on FixYa.
Feel free to contact me directly.We're happy to help you with free advice and we'd appreciate your thoughtful rating of our answer.
William E. Miller[email protected]http://www.microwavedisplay.com