The problem has now changed to this: the microwave works normally except that now if I am not cooking and open the door to put food in the microwave "turns on" while the door is open. By that I mean that the loud fan that normally comes on inside the cooking area comes on and the turntable begins rotating and the light is on - when the door is open! I was worried that actual microwaves were being produced but a cup of water was not heated so I think that no radiation is being produced. Other than this my microwave works normally and I can cook a meal fine. Is this a switch or the logic on the circuit board or what? Thanks. I would like to buy the right part for the repair.

try here for more info. Complete Microwave Oven Troubleshooting, Repair and Information and http://www.microwavedisplay.com/ .

A lot of microwaves will have a schematic inside the cover. It could be the relay, a door switch,the high voltage transformer, high voltage diode, or the magnetron. Typically if its the transformer or the magnetron , the cost of either is usually not much less than a new oven. The relay can sometimes mean replacing the circuit board which is a high cost item.

CAUTION CAPACITOR MAY HAVE LETHAL CHARGE (Clik on the 2 links above i sent you to find how to safely short the capacitor terminals)

To test the relay, unplug the oven, remove the cover, discharge the high voltage capacitor, and disconnect the wires from 2 terminals at the 120 volt ac side of the high voltage transformer. Set your volt meter to read 120 VAC and connect the voltmeter leads to the wires you disconnected. Make sure the bare ends of the wire connectors dont touch each other or ground. I usually use a couple of sheets of folded notebook paper to keep the leads separated and from other metal parts of the cabinet. Now plug the microwave back to the 120vac source, put a cup of water in the oven, and start it up. If you see nominal 120 VAC on the meter your keypad and relay is working. If no 120 vac then the relay or something on the keypad has failed.

unplug your microwave and disconnect your meter and reconnect the wires. I noticed that you didnt check the door switches for continuity or change of state with door opened or closed. there is usually 3 switches. some may have 3 terminals but use only 2, so look very close before remove a wire from the switch so you can get back on the right terminal. you usually only need to unplug the wires from one switch terminal to check it with your ohm meter. typically the top and bottom switches are closed with the door closed and open with the door open. the center switch is open with door closed and closed with door open. It is the one that usually trips the breaker if the door is open and the fan and turn table are running. Which didnt happen in your case.

Thank you for all the info. I believe all 3 of my switches behave : closed when door closed, then open. So maybe that is the problem? But all three swictches are functioning as tested by my VOM. Now I don't think I had removed any wires before the problems occurred but you info about the middle switch makes me wonder if I changed something. I am going to go back and check but I believe my plugs prevent the wires from being reconnected backwards. I better check on that. Now here is a last note: my complaint is that the fan and light run when the door is open (not the magnetron though) but this problem can be remedied if I pull the wires from the top switch and replace it - as I've done - with a switch that leads outside the cabinet. I can thenm switch off the fan/light manually. I'm thinking this indicates a board problem since the microwave switch is opening and closing properly, so that only leaves the board as a suspect. I ordered a used board of Craig's list and it will be here in a week.

Hi - what cover might I look under? I don't see any diagram so far. I didn't check for voltage from the board because when i fool the switch witht he door closed the food cooks properly.