Troubleshooting a nukular oven that no longer heats

Old 02-22-17, 08:05 AM
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Troubleshooting a nukular oven that no longer heats

My mom's microwave oven stopped heating. It looks to be working normally -- display, lights, turntable, exhaust fan -- but nothing gets hot. It's a Hamilton Beach from Wally World.

The magnetron still looks new, no signs that the smoke has escaped. I tested it with my el-cheapo Craftsman DMM and I get OR from either post to the outer case, and 10-ish Ohms between the posts. Dr. YouTube says this means the magentron isn't burned out (but I struggle to diagnose a burned-out light bulb). The thermal fuse, OTOH, tests 40-ish Ohms.

Does this sound like a bad thermal fuse to you? I've checked ebay and I can replace it for less than $10. Is there any harm in reassembling the mike, shorting across the thermal fuse and (briefly) testing it to confirm the fuse in fact is the cause?
Old 02-22-17, 06:38 PM
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The magnetron filament should be around 1 ohm.

If the thermal fuse measures 40 ohms it's bad.
A thermal fuse is a fuse which should measure close to 0 ohms.

Typically.... the thermal fuse, if bad, will cause the entire unit to be dead.
The fuse should be a 15A or 20A white ceramic type.

There are several parts that can cause no heat.
High voltage transformer
High voltage capacitor
High voltage diode.

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