I have one of those 15 years old range top microwaves from Kenmore.
model # 721.8915580.
It blacked out during use and I found out the fuse had burned up.
I purchased the appropriate fuses from Radio Shack and replaced it with no problem.
Now the fuse blows up again and again.
When I put a new one in, the lights and the fan work fine. the display is alive. when I start the microwave, it works for a 2 or 3 seconds than makes an unusual rumbling sound and goes black again, blowing up the fuse.
Is it the magnetron or a diode that has gone bad??
I have the list of parts for that model, I just need to know what part to purchase.
thanks!

The loud hum would indicate a bad capacitor or diode.Magnatron maybe but not likely.

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thing to do is isolate the faulty part of the circuit......disconnect the feed to the ht transformer,replace your fuse and switch on-set the unit cooking on high ....if it runs ok without fusblowing reconnect the transformer.
disconnect the ht feed to the capacitor,disconnect the two wires connecting the mag(make note of which way round they go) and switch on again setting it on high for a short while-if it blows the fuse again replace the ht transformer-if not then reconnect the ht capacitor and try again-if it blows again check the capacitor for sc,the diode for sc and the asm rectifier(if fitted across the capacitor)for sc-if still no fuse blowing then the magnetron is at fault-check continuity of filament to case-if there is a reading throw the mag away and replace it.

regards mike

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