This is a microhood that stopped heating. No odd sounds, but of course the magnetron is not firing, so the thing is quieter when I attempt to heat up food.

I took the case off, found the cover for the magnetron and the diode, and discovered that the magnetron seemed to be fine with an ohm check. The diode showed open in both directions. The HV capacitor showed good (1.04 microfarads and 1.05 is printed on the cap).

So I replaced the bad diode. Well, I put the case back on and tried to heat some water. It didn't work. I took it back apart and the new diode is showing open in both directions.

I guess I just fried a second diode. What could be the problem? All I see in the compartment is a huge transformer, which I thought would be the low voltage transformer. But from what I am gathering, that could be the one and only transformer in the machine, and it costs $170. But I don't know the procedure to test it or figure out why diodes are going bad.

The one thing I do know for this microwave is that the HV capacitor doesn't seem to be getting up to a high voltage. When I discharge it, I don't see or hear anything, but I am too scared to do a voltage test with my DVM on the chance that there is over 1000 volts on it.

Oh, and when I did my test, I tried heating the water at 50% power. I could hear a soft click everytime the magnetron was supposed to cycle on or off, but obviously there was no heating whatsoever and it didn't turn on.

And after further review, I found out that the magnetron temperature sensor is open. It was probably bad the first time and I hadn't discovered it. I don't see how this is related to a bad diode, unless the magnetron is somehow giving fits. Its filaments measure almost a dead short, which I presumed was fine. Is this all evidence of a failing magnetron drawing too much current and giving off too much heat?

Hi,

The transformer is a high voltage transformer, be careful.

The capacitor more then likely has a built in resistor to keep it from holding a charge.

If you have 120 Volts into the transformer then you have a high voltage problem, most likely the transformer.

Ok, I did some research. I don't see it listed on the poorly-drawn "exploded" views which don't show it as far as I see.

I believe it is Whirlpool part #560192, but that doesn't come up on any search. The three temperature sensors listed on the parts diagrams seem to be for different parts of the microwave. Two go inside the recirculating air to sense food (cavity thermostat 1&2), one is for the exhaust fan, and there is a 3-pin humidity sensor. The second cavity thermostat seems to be a new item, because it only shows up on the Tech Sheet supplement.

Printed on the bad thermostat is:
36TX21 (See note below)
560192
L125-40C
S9927

Note: I think that this specifies the size & shape of a standard thermal cutout switch with 125 volts and 40 degrees Celsius as its proper operating characteristics. "S9927" is apparently a 1999 date code. While I don't see this particular part at AppliancePartsPros, it's not like a big money maker from what I see online. :)

Here is a website that calls it a "Thermodisc" which rings a bell with me. See Thermodisc 36TX21 L125-25F
I think that I have replaced my dryer's thermodisc by buying parts from ApplicancePartsPros, so I wonder if you have tons of these in stock?

I guess I might need to find one that has the correct temperature setting, namely 40C. And I guess these discs are supposed to auto reset to a dead short when they are still working and below the setpoint.

Oh, here is the datasheet for the THERMODISC brand 36T. It explains it on page 16 of the pdf. See http://www.thermodisc.com/en-US...36T_Product_Bulletin.pdf - made in USA?!

SUCCESS!! I was able to bypass the bad magnetron thermal cutoff with a short piece of wire and it works. I heated up some water and tested 50% power again. Much better. So I need to order this part ASAP.

Wow, that's hotter than I thought. I figured the 125 was for voltage. Anyway, I chatted with someone and I ordered the part. She found the diagram that the part was on, and it was clearly the right part AP3038827. I am glad to have it on the way. Still a lot cheaper than a magnetron. Speaking of that, I guess this thermostat is designed to keep the magnetron from breaking, so in some ways it worked as designed in that respect.

Well, this is not supposed to "blow" or actually ever go bad... it is rated 100,000 cycles. So this was likely a faulty component that decided to go bad for whatever reason. I don't think it is necessarily related to the magnetron status.