Recommended repair or magnetron replacement of broken microwave (Jenn-Air M170B)

An inverter is a switched SWITCHED POWER SUPPLY. More efficiency less weight, no big expensive power transformer. A magnetron has to be run full power. You just turn it on an off as needed.

In troubleshooting my brothers microwave, I forgot the exact steps we took. Ended up wasting money before finding out transformer was bad.

Greg

Reply to
gregz
Loading thread data ...

"When it doesn't heat..." Do you mean the microwave does everything else EXCEPT heat the contents? That is does if LOOK like it's working, turntable goes round, light comes on, timer works? If so, replacing the magnetron is a good first guess.

I say this because the other stuff is governed by a printed circuit board that has three to ten dodgy electrolytic capacitors on it. Replacing these capacitors is pretty easy and pretty cheap.

Reply to
HeyBub

Ah, there was something there.

formatting link
But it looks more like a rectangular ceramic resistor than a tubular diode.

I haven't measured it due to the warnings about the charge on the capacitor.

Today I looked at Lowes but they didn't have any black 22 inch by 13 inch microwaves. The size seems to be the biggest hurdle.

Reply to
Danny D.

Yes. EVERYTHING, fan, lights, table, controls, etc. ... everything else is working. The only thing that is not working is nothing gets heated.

Reply to
Danny D.

Could be the magnetron, altho the usual failure is a gradual decrease in power output so thing take longer and longer to get hot. If you can locate the two wires going to the magnetron filament, you should see someting less than 100 ohms for the filament. But, you have to disconnect one wire from the filament to the power transformer before you check the filament or you will just see the resistance of the transformer and not the filament of the magnetron.

Reply to
hrhofmann

When my JC Penny unit quit working, it turned out to be the fuse & fuse block--badly corroded. Replaced both 5 years ago, and they're still going strong.

Reply to
croy

That's the diode I saw in the pictures and the diagram. Diodes come in all shapes and sizes. ^_^

TDD

Reply to
The Daring Dufas

Ah. Thanks. I'll figure out how to discharge the capacitor first. It has been sitting all day, so maybe by tomorrow it will have discharged. My Fluke DMM has a diode test mode, so I can at least run that baseline.

Reply to
Danny D.

I was wondering WHERE the magnetron lay.

If these are the magnetron leads, they read 0.4 ohms with the Fluke in ohms mode:

formatting link
And, the diode reads OL in both directions, both forward biased and reverse biased with the Fluke 75 in the diode mode:
formatting link

Reply to
Danny D.

The safest way is to use a 100k ohm resistor across the capacitor then check for residual voltage with your DVM. There is always The Jesus Method for discharging caps. ^_^

TDD

Reply to
The Daring Dufas

If you are only on the filiment of the megatron and not in the circuit it is probably ok. If the megatron is still connected, you may be meauring the filiment windings of the transformer.

Some high voltage diodes are made of several lower voltage units in series in the same case. The diode function of the Fluke may not have enough voltage to check this out and will show open. Here is one way to check to see if it is actually open.

formatting link
They use a 9 volt battery and the voltage scale of the meter, One way will show open and the other will show a few volts less than 9 if the diode is good.

Reply to
Ralph Mowery

That looks more like a "block diagram" than a schematic. If you didn't find a folded up paper schematic tucked inside somewhere, then go online and find one. I've read other responses, but I'm sticking with a faulty thermal cutoff as most likely culprit.

Reply to
Smitty Two

Um, isn't "Megatron" one of the living robot Transformer creatures? ^_^

TDD

Reply to
The Daring Dufas

That's a nice procedure which I will try in the morning. Thanks for pointing it out - as I would have thought the basic diode function of the Fluke 75 would have sufficed.

At the moment, it shows the diode as bad - but - as you noted - that may be an anomaly due to the voltage of the Fluke in diode mode.

Reply to
Danny D.

From your wiring diagram that you posted earlier, the square black thing is more likely a high voltage diode. If that goes out, the microwave hums, but doesn't heat. If the diode goes, I'd expect the cap to lose its charge. You might have to slice off the heat shrink to reveal the diode markings on it. Dash, triangle, bar, dash. Somewhat like --|>|-- more or less.

Christopher A. Young Learn more about Jesus

formatting link
.

Ah, there was something there.

formatting link
But it looks more like a rectangular ceramic resistor than a tubular diode.

I haven't measured it due to the warnings about the charge on the capacitor.

Today I looked at Lowes but they didn't have any black 22 inch by 13 inch microwaves. The size seems to be the biggest hurdle.

Reply to
Stormin Mormon

And, all have personal self worth, and self esteem. Until they go bad. And then they go to a local school and spray every one with electrons. Using a high power transformer and......

Christopher A. Young Learn more about Jesus

formatting link
.

That's the diode I saw in the pictures and the diagram. Diodes come in all shapes and sizes. ^_^

TDD

Reply to
Stormin Mormon

Should be infinite ohms one way, and then reverse the leads, and get some where between 2k (about that) ohms the other way. My SWAG at the moment is the diode went. If the diode shorted, the cap may be discharged now.

Christopher A. Young Learn more about Jesus

formatting link
.

Ah. Thanks. I'll figure out how to discharge the capacitor first. It has been sitting all day, so maybe by tomorrow it will have discharged. My Fluke DMM has a diode test mode, so I can at least run that baseline.

Reply to
Stormin Mormon

Cookie! Cookie!

formatting link
Christopher A. Young Learn more about Jesus
formatting link
.

The safest way is to use a 100k ohm resistor across the capacitor then check for residual voltage with your DVM. There is always The Jesus Method for discharging caps. ^_^

TDD

Reply to
Stormin Mormon

Why do you say that? It sure looks like a schematic to me. It shows the various components and the circuit connections between them.

If you didn't

Reply to
trader4

Seems a little light on detail.

Reply to
Smitty Two

HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.