Tip & How-To about Microwave Ovens

How to replace a bad magnetron.

When sparks fly out of the port inside the microwave chamber you have a burned out magnetron. They are not hard to replace, but also are not cheap, so first you should check the following to make sure you do not have bigger problems. All the parts you need to check should be behind the control panel display. First you need to check the transformer to make sure it did not short. Using a DMM on ohms scale, disconnect one lead on each side of the transformer. If the transformer is OK it should read more than 0 ohms, say 2 or 3. If OK, check the High Voltage diode and replace if necessary. It should not be shorted but it will not check like a normal diode on forward current. As long as it isn't shorted it should be OK. Of course the fuse will need to be checked and replaced with the exact same value of ceramic fuse (not glass). All parts can be purchased at www.repairclinic.com . If all these components check OK you need to replace the magnetron. It is the large silver box on the side of the oven cavity, in the same area as the parts you have been checking, and has cooling fins on the perimeter. You will have to decide if it is cost effective to replace the magnetron. This site www.repairclinic.com should also have them. If they do not try www.partstore.com . The magnetron should come out easily with a few bolts and two wires to disconnect. When installing the new unit follow the instructions carefully and make sure the surfaces mate perfectly. You do not want stray microwaves bouncing around in the kitchen. At this point your unit should be back to working. I did not address the control panel.

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Check inside the oven chamber and look for missing powder paint or signs of arcing, if so there is a paint to repair microwaves for this issue or else just dispose of the microwave. If the inside is good remove all the screws and remove the cover. If the magnetron was making louder noises prior then replace the magnetron. the giant capacitor could be bad. While the cabinet is open make sure to look for burned wires, check the continuity of thermal cutoffs, and check the main circuit-board for burned traces or components. The relays in most electronics are known for arcing (spot welding) and staying in the wrong position. Tap them hard with the back end of a screwdriver. During all of this use safe electrical practices by having the power cord unplugged. The capacitor could still have a high charge on it so be careful.

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Then you have blown a fuse. Check inside the oven chamber and look for missing powder paint or signs of arcing, if so dispose of the microwave. If the inside is good remove all the screws and remove the cover. Replace the fuse. If the magnetron was making louder noises prior then replace the magnetron. Since the fuse went the giant capacitor is likely bad. While the cabinet is open make sure to look for burned wires, check the continuity of thermal cutoffs, and check the main circuit-board for burned traces or components. The relays in most electronics are known for arcing (spot welding) and staying in the wrong position. Tap them hard with the back end of a screwdriver. During all of this use safe electrical practices by having the power cord unplugged. The capacitor could still have a high charge on it so be careful.

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Then you have blown a fuse. Check inside the oven chamber and look for missing powder paint or signs of arcing, if so dispose of the microwave. If the inside is good remove all the screws and remove the cover. Replace the fuse. If the magnetron was making louder noises prior then replace the magnetron. Since the fuse went the giant capacitor is likely bad. While the cabinet is open make sure to look for burned wires, check the continuity of thermal cutoffs, and check the main circuit-board for burned traces or components. The relays in most electronics are known for arcing (spot welding) and staying in the wrong position. Tap them hard with the back end of a screwdriver. During all of this use safe electrical practices by having the power cord unplugged. The capacitor could still have a high charge on it so be careful.

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Then you have blown a fuse. Check inside the oven chamber and look for missing powder paint or signs of arcing, if so dispose of the microwave. If the inside is good remove all the screws and remove the cover. Replace the fuse. If the magnetron was making louder noises prior then replace the magnetron. Since the fuse went the giant capacitor is likely bad. While the cabinet is open make sure to look for burned wires, check the continuity of thermal cutoffs, and check the main circuit-board for burned traces or components. The relays in most electronics are known for arcing (spot welding) and staying in the wrong position. Tap them hard with the back end of a screwdriver. During all of this use safe electrical practices by having the power cord unplugged. The capacitor could still have a high charge on it so be careful.

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