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Kenmore microwave acting intermittently

Okay, so I've tried everything possible to get a microwave that was picked up off the street to work. It's a Kenmore 565.8925590, 1300W, serial 1V7C01490, manufactured September 1991. The magnetron and controller IC are made by Sanyo, so I imagine that the entire oven was, too. So, here's the symptoms the microwave exhibits: The microwave will happily begin to microwave a cup of water. After about a minute or so, the fan and the turntable will stop. The light stays on, and the counter keeps going. If I stop the microwave cycle and let the oven cool down, I can start it up again, for about another minute. So, I opened it up, and checked the usual suspects (fuse, interlock switches, etc.) The primary interlock switch was always open, so I replaced it. That didn't fix anything. All of the switches appear to be making good contact with the actuators on the door. There are two thermal protectors. Both offer a resistance of zero, and according to the schematic (and the actual wire routing) if either opened, it would kill power to the entire oven--so I know that they are not at fault here. The magnetron does become hot to the touch, but it's not _that_ (135 degrees centigrade) hot. As far as I can tell, the only thing left to be at fault is the relays, that are located on the controller board. I'm a little leery of testing the relays on it with the oven live--especially because the warning labels clearly state that the step-down transformer will give me a jolt. :-) There is a burn mark on the PCB in the center, but the resistors, diodes, and caps in that area all test fine.

Any suggestions?

Thanks!

--Chris

Reply to
Beanie
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Sounds like one of the thermostats inside the case is bad. Could also be a bad transformer.

Reply to
Astriapo

What powers the stirrer and turntable? Do they have their own power supply separate from everything else?

Does the magenetron continue to operate?

PS: Thanks for giving a clear description of what happened and what you did. Most people don't!

Reply to
William Sommerwerck

Or an intermittent filament connection to the magnetron.

Put it on 50 percent power and listen carefully for the sound as the magnetron kicks in. There should be a subtle change in the hum as the filament heats up and the magnetron starts drawing power. I bet that will be absent once it stops heating. Of course, could also be a bad transformer, relay, other wiring, etc. This should be repariable relatively easily though. Inexpensively unless it's a bad transformer or an intermittent filament inside the magnetron.

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Reply to
Sam Goldwasser

I've been seeing a lot of bad solder joints on the control boards in microwaves lately. I think it's due to the switch to lead-free solder.

Reply to
James Sweet

I was either reading something on the net or shopping for something and read the features of whatever it was touting that it was made entirely with lead-free solder. I though OH BOY to myself, is that something to advertise on?

Reply to
Meat Plow

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