Microwave repair

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** You'll need an ohm meter test to tell if a ceramic case fuse is blown. Any 15A ceramic of the correct size will work, but best find a HRC ( high rupture current) type.

...... Phil

LOL You are a trip. I've already ordered some fuses. Enjoy.

The only other option is the door switches. Seems they use three. Two are actuated when the door latch is fully engaged, one on each side of the line. Another is deactivated when the latch is first engaged, i.e. latch is pushed in, but not fully latched. This one shorts the circuit side of the other two switches. I can't get why this is there, other than to act as a crowbar in case the other two don't work and power is applied with the door open.

I can't verify that one of the line switches is working. Looks like the plastic mechanism is not moving to activate the switch. But it's hard to reach, so I'll try the fuse first. Besides, according to the schematic, the fuse, timer switch and pilot light are on the power input side of the door switches, so the light would come on anytime the timer switch is closed and the unit is plugged in... if the fuse is good. I'm not seeing a pilot light. I suppose the pilot light could be failed, but neon bulbs typically last a long time.

Sigh... I little use of internet search engines can often help here:

That third which is present *exactly* to be a crowbar to prevent power application with the door open.

A DVM (with thermocouple input) is a fundamental home appliance. As is a bench power supply, a Dremel, some test leads, and a glue gun.

I've considered having a cheap LCD oscilloscope around, but it would be rarely or never used at home.

Why are you sighing? I sussed out what the switch does and you confirmed it. Thank you.

Other than checking the fuse, it would all be pointless here, because I can't get to the switches to probe. Easier to just give the fuse a try, then toss the unit in the bin if that doesn't fix it.

Like I've said, the microwave has a debugging tool built in, the pilot light, which says it's the fuse.

Such protective fuses seldom blow without a very good reason. Usually that the magnetron PSU has failed in some interesting way.

I had one fail that way and repaired under warrantee.

Replacing the fuse may only result in blowing it again immediately.

What is your point? Are you suggesting I try replacing the power supply to prevent wasting a fuse?

On the one I had for years (an Amana commercial microwave) the fuse blew for the reason others have mentioned.

Part of the door-switch assembly failed (some plastic wore down, I think), and the "disconnect the mains if the door is opened" switch didn't open properly when the door was opened.

The secondary (safety) switch in the door-switch assembly operated as intended. It was/is designed to close (creating a short circuit across the power to the magnetron) an instant after the primary switch is supposed to open. Since the primary was still closed, the secondary shorted the supply and blew the fuse.

I replaced the fuse (figuring that it might have just been an age-related failure). Nope. The microwave worked OK for a day or so, but the next time somebody opened the door before pushing the "off" button, the fuse blew again.

Replacing the failing switch (or its actuator) wasn't practical or safe, as they aren't made available separately. The tech replaced the whole multi-switch assembly, and the microwave worked fine for several years more. The cost (including service) was about a quarter of the cost of a new microwave of equivalent type.

The fuse on ours blew and I found a replacement at Home Depot. They had a couple of ones labeled for microwave use - I got the one that matched the part number (it had several part numbers on the label).

It seems it just died of old age (~15-20 yr). The replacement has worked fine for several month and is still going.

Which was what?

This is actually two switches. So they both had to fail.

The switches can be bought. They come with many lever arrangements, so you have to match up to the one in the oven, but they are not so hard to find. The problem is getting to the suckers. I'm pretty lazy when it comes to this sort of repair. My concern is one of the primary safety switches does not seem to be activating because of the plastic bits I can't see. So if the fuse doesn't repair it, it's going in the bin.

I tried getting a friend's microwave repaired last year and there was no one who works on these anymore. Most microwaves sold are under $100, so not much room for profit in repairing them.

I wouldn't even have bothered with the fuse, but I can't find one with dial controls, medium sized internal dimensions and a sub $300 price tag.

Standard UL single fault abnormals allows replacing fuse once.

RL

Sometimes a fuse may blow because it is old so to speak. I had an amplifier that ran on 12 volts DC. About every 2 months the fuse would open up. Nothing wrong with the amp. The fuse was rated for 20 amps and the amp draw was 15 amps. The fuse and holder would get warm and looing in the glass fuse it looked like the fuse just sagged out.

Where I worked sometimes the circuit breakers on equipment would trip. If a quick check with an ohmeter did not show a problem it was recommended we reset the breaker. Often that was all it took. This is on 480 volt 3 phase equipment that could be from 5 amps to 200 amps.