Kenmore elite over range microwave quit after buzzing & zap noise. Would not heat water. Repair man ordered and installed inverter board and magnetron. While he installed parts I tried to clean off grease on various parts. After installing parts and buttoning it back up, remounting we tried to cook but blew the circuit breaker, reset it and blew again. However the touchpad, clock, exhaust fan and lights work. He then said cost too much to repair. I replaced the 20 amp ceramic fuse and ran the keypad diagnostics. After entering test mode it shows 6183 with small 3 on upper right. I test all functions and get the "OK " 8 on the display. When I test #3 on number pad I blow the house circuit breaker. It looks like it tests relay 4903 on the power and display PCB. Other numbers on key pad test without triping circuit breaker . Am I correct? My wife thinks it is unsafe and fears fire disaster. Is it worth repair and can I safely use the exhaust fan and lights. Seems like something in the cooking circuit is bad. PS- I asked the repair man about discharging the capacitor and he said no need since there is a power inverter board. Thanks.