Does my microwave diode look good to you?

I just tested my microwave diode where, unfortunately, it seems to be good:

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Forward biased with a 9 VDC battery, I measure 7 VDC across the diode; reverse biased, I read 9 VDC across the diode (given a 200 ohm current-limiting resistance in series with the battery).

I was hoping the diode was bad, because otherwise, I don't know what's wrong with the microwave. It does everything but heat up the food.

It makes noise, the lights light up fine, the controls all work, and it beeps when done, etc. - but it just won't heat up anything.

Did I test the diode properly?

Reply to
Danny D.
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Reply to
Danny D.

if it does everything but heat it might be the magnatron

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Reply to
ChairMan

see other post for picture.

Since apparently there is no current in that direction, how about taking out the resistor and seeing what it says then?

Normally I'd say you should measure the voltages while it's in the circuit. That's a little different here since you'd have to have the cover off and that would expose you to a lot of microwaves. OTOH, it's not working so maybe there are no microwaves. I hate to rely on maybe. Do you have a microwave detector. I got one at Radio Shack about 30 years ago and it works well. I was able to test it because at that time I had Amana Model 2, and it didn't have door latches on it. So I could open the door a little before the safety switches turned the machine off, and I could see the detector reading rise from zero to at least half way across the scale (but I only allowed that for a second.) After that, I could check door leakage. RS doesn't still sell them iirc but you might find one used, or you might find a new one sold through another channel.

Here's exactly the same one I have, no bids yet, 18 hours left from my post time. If it doesnt' sell he'll probably relist it so click anyhow.

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and a new one for only 15 including shipping

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Here's one for more, $35

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And

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I'm self-taught for the most part, but I would have just measured the resistance directly with an ohmmeter, using the meter's internal battery, in both directions. If one direction is many times higher than the other, it's good. Even if I did it your way, I would do it my way too, to see if the results confirmed each other.

For more info, ask on sci.electronics.repair

***I used to have an Amana Radarrange model 2. I never saw a model 1, but this one looked just like the image of a microwave everyone used for years (except compeititors).

I got it used, fixed the door spring and had it for about 10 years. When it stopped working I called Amana and asked, figuring she might know which part failed most frequently. She suspected the magnetron. The next time I called, someone suspected the diode. I opened the high voltage cage**** and saw that there were cracks on the wires to the diode (one 20 or 30 times bigger than yours, counting heat radiation fins). I used silicione sealant by GE (available in black at auto parts stores, if color matters to the repairer) and put on large blobs of it, thicker than the thick wires. And it worked for another 10 years.

****The woman at Amana was very much afraid I wouldn't put the woven metal gasket back the way it had been and that it would leak. She also wouldn't send me a schematic. I had to promise her up and down that I had 20 years experience with electronics, and I would put the gasket just where it was, and she finally sent me a schematic, for free. I had to take apart another one^^ and I think they are designed differently now, but I would be very careful reassembling so as to not leak microwaves.

The next time it failed it did nothing, so it was the transformer. I think Amana wanted 380 dollars I said, "That's the price from 1970. They are worth less now (since you can buy a whole microwave for under

100.) After writing a letter -- I said, Save a few for your museum and the inventor's grandchildren and sell the rest at a price at which you will actually sell them -- and being referred to a place near Harrisburg, they lowered the price to the wholesale price, 250 or so. Much as I hated to part with model 2, I scrapped it.

^^This latest one has a bad relay, and I'll probably never get around to fixining it.

Reply to
micky

What do you mean by a "microwave diode"?

To me, it's a point-contact diode used in microwave measurements. My experience has been that sample-to-sample variation is high.

Reply to
William Sommerwerck

"microwave diode" can mean many things to me since I've experience in electronics. The context in which it's being used in this thread is a discussion of the high voltage diode used in the power supply for the magnetron in a homeowner's microwave oven. ^_^

TDD

Reply to
The Daring Dufas

I meant the high-voltage diode in the microwave oven.

Reply to
Danny D.

The resistor is to prevent the diode from burning up with too much current, I believe.

If I take out the resistor, I probably blow up the diode.

That does not sound like good advice, so I didn't read the rest of the suggestions for fear of being led astray.

Reply to
Danny D.

It would be difficult for most people to measure the voltage while the microwave is running. Not counting on any stray radiation,but at the voltages in the microwave, it would burn out most meters. Also the high voltage would most likely go through the insulation and into the person doing the measuring. Very few meters that are found are rated for much over 1000 volts, less than half of what is used in many microwaves.

The ohmmeter in the common meters will not check the diode either. The voltage drop across the diode in the microwave is more than the meter is set up to measure in the ohms range. It is not around .7 volts as one would find in the lower voltage diodes. Internally the diode is made up of several diodes so the voltage drop is much more.

Reply to
Ralph Mowery

"Arfa Daily"

** The OP is just begging for a Darwin Award.

So who are you to spoil his one moment of fame ??

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How amazing to find that the famous Award originates with USENET !!!!!!!

.... Phil

Reply to
Phil Allison

That's true of most DMMs, but there are exceptions. My Keithley 2000 will bias a diode up to 10VDC. Useful for checking smaller zeners as well.

Reply to
JW

Sort of. A 9 volt battery isn't really a good test for a high voltage recifier. The forward drop will exceed that of that battery, at least a rated current of 0.3 to 0.5A, depending on the diode and oven.

The results of your test though, show the diode isn't open and isn't shorted, so that's good. I'd not bother to replace the diode at this point of the oven was in front of me.

I'd test the heater coil of the magnetron. It should measure close to dead short ohms if it's good. If it's open, well, that explains why there's no heat. You'd also want to make sure the transformer is even being turned on, you can usually tell this from just listening to the oven or watching lights flicker when the oven turns on.

Be sure you discarge the cap before you mess around in a microwave oven.

As mentioned in this thread by others, a normal volt meter cannot be safely used to test the HV section of a microwave. You really don't even need to for the most part either.

Reply to
Cydrome Leader

see other post for picture.

Since apparently there is no current in that direction, how about taking out the resistor and seeing what it says then?

Normally I'd say you should measure the voltages while it's in the circuit. That's a little different here since you'd have to have the cover off and that would expose you to a lot of microwaves. OTOH, it's not working so maybe there are no microwaves. I hate to rely on maybe. Do you have a microwave detector. I got one at Radio Shack about 30 years ago and it works well. I was able to test it because at that time I had Amana Model 2, and it didn't have door latches on it. So I could open the door a little before the safety switches turned the machine off, and I could see the detector reading rise from zero to at least half way across the scale (but I only allowed that for a second.) After that, I could check door leakage. RS doesn't still sell them iirc but you might find one used, or you might find a new one sold through another channel.

Here's exactly the same one I have, no bids yet, 18 hours left from my post time. If it doesnt' sell he'll probably relist it so click anyhow.

formatting link

and a new one for only 15 including shipping

formatting link

Here's one for more, $35

formatting link

And

formatting link

I'm self-taught for the most part, but I would have just measured the resistance directly with an ohmmeter, using the meter's internal battery, in both directions. If one direction is many times higher than the other, it's good. Even if I did it your way, I would do it my way too, to see if the results confirmed each other.

For more info, ask on sci.electronics.repair

***I used to have an Amana Radarrange model 2. I never saw a model 1, but this one looked just like the image of a microwave everyone used for years (except compeititors).

I got it used, fixed the door spring and had it for about 10 years. When it stopped working I called Amana and asked, figuring she might know which part failed most frequently. She suspected the magnetron. The next time I called, someone suspected the diode. I opened the high voltage cage**** and saw that there were cracks on the wires to the diode (one 20 or 30 times bigger than yours, counting heat radiation fins). I used silicione sealant by GE (available in black at auto parts stores, if color matters to the repairer) and put on large blobs of it, thicker than the thick wires. And it worked for another 10 years.

****The woman at Amana was very much afraid I wouldn't put the woven metal gasket back the way it had been and that it would leak. She also wouldn't send me a schematic. I had to promise her up and down that I had 20 years experience with electronics, and I would put the gasket just where it was, and she finally sent me a schematic, for free. I had to take apart another one^^ and I think they are designed differently now, but I would be very careful reassembling so as to not leak microwaves.

The next time it failed it did nothing, so it was the transformer. I think Amana wanted 380 dollars I said, "That's the price from 1970. They are worth less now (since you can buy a whole microwave for under

100.) After writing a letter -- I said, Save a few for your museum and the inventor's grandchildren and sell the rest at a price at which you will actually sell them -- and being referred to a place near Harrisburg, they lowered the price to the wholesale price, 250 or so. Much as I hated to part with model 2, I scrapped it.

^^This latest one has a bad relay, and I'll probably never get around to fixining it.

Reply to
micky

I think so too.

Now why would you think that? Did you fail to notice that if there is 9 volts across the diode, there is no current running through the diode. How can you imagine that removing a 200 ohm resistorr will increase the current much? And with a 9-volt battery no less.

Since ;your answer does not sound like you think well, I won't read the rest of your posts, for fear I'll read foolishness but be too weak to avoid believing it. .

Reply to
micky

Thanks for that confirmation. Bummer. But now at least I know it's most likely the magnetron.

Reply to
Danny D.

Except there isn't 9 volts across the diode. There was 7 volts across the diode.

Reply to
Danny D.

That was forward biased. My reply was clearly about reverse biased. If you hadn't snipped so much and didn't want so much for me to be wrong, you'd have noticed.

Quote

End Quote.

I added the blank line between your first and second line so there'd be no doubt which direction I was talking about.

Reply to
micky

Would it make sense to hook the diode to a 9 v transistor battery in each polarity, and measure the milliamps current in each direction?

. Christopher A. Young Learn about Jesus

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Reply to
Stormin Mormon

"Normal" diodes would fry under those circumstances; but I don't know what would happen with high-voltage diodes. That's why I have the resistor there.

Reply to
Danny D.

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