Have a Kenmore 721.67680790 lost all power is there a fuse somewhere?
Microwave ovens have both electrical and thermal fuses. The former are usually cylindrical (1/4" x 1 1/4" or 5 mm x 20 mm) and mounted in a clip-type holder. The latter are either rectangular ceramic blocks about the same size as an electrical fuse, or metal and plastic cans about 9/16" in diameter with blade-type electrical terminals on top and a diamond-shaped metal mounting plate on the bottom. They are usually mounted on or near the magnetron or on top of the oven cavity.
Do not test by replacement; use an ohmmeter or continuity tester to check the fuse.
If the electrical fuse is blown, check the high-voltage capacitor behind the big transformer for a short circuit. Caution: discharge it through a large resistor before touching the terminals with your fingers or an instrument other than a high-voltage probe. If you see a spark when you touch the discharge lead to the capacitor, you can stop that test; the capacitor is NOT shorted, although it's internal safety discharge resistor may be open. If you don't see a spark, set your digital multimeter to its highest DC voltage range and confirm that the capacitor is discharge, then set it to resistance to check for a short. A good capacitor will have a constantly increasing resistance reading until it finally settles on a number above 1 million ohms (internal discharge resistor); a bad one will quickly settle on a very low value. (A continuity tester may give a brief indication of continuity as the capacitor starts to charge, then show "open".)
Inspect the door switches to make sure they aren't broken or burned. I've seen them literally fall apart - the contacts start going bad, get hot, deteriorate further and eventually cause the plastic case of the switch to fail. Usually you have trouble getting the oven to work properly when this happens, but it's possible the first sign of failure is a short to ground from a terminal that fell off the switch, and a blown fuse. Inspect the rest of the wiring for anomalies as well. If you can't find any shorts to ground or across the power line (don't be fooled by the low resistance of the controller transformer), then you can try replacing the fuse.
Again, use an ohmmeter or continuity tester to check these. Thermal fuses can go out simply because the oven got over-worked in a hot environment, especially if the cooling vents were blocked or the fan is not turning fast enough. Clean the vents and magnetron fins if necessary, and make sure the fan spins freely and easily.
Dec 06, 2010 |
Kenmore Microwave Ovens