cold microwave

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Stormin Mormon wrote:

Here's a way to test the HV diodes in a microwave. Don't kill yourself. I'm not sure if 6 volts would work with a color TV HV diode since they go up over 35,000 volts
http://www.gallawa.com/microtech/diode.html
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======================================================================
That site reads, in part, "Testing the HV diode requires an ohm meter with at least a 6 volt battery in order to accurately measure the front to back resistance of the diode. Meters with insufficient battery power may read infinite resistance (open) in each direction, mistakenly showing a good diode as being open."
It also reads; "IMPORTANT SAFETY INFORMATION: Microwave ovens are among the most dangerous appliances to work on. Before attempting any troubleshooting, testing or repairs, for your personal safety, we strongly urge you to carefully read the very important safety precautions found by clicking here and Please read our disclaimer at the bottom of this page.
Please be very careful. A microwave oven is essentially a 1000 watt transmitter in a metal box. With DC voltages up to 5000 volts at amperage that can easily kill. Also microwave radiation at wavelength of about 13 centimetres (approx. 5 inches) that can cook meat, including you. And fry human eyeballs .............. cataracts anyone!
More often we have found defective door micro-switches and faulty over- heat devices and or the magnetrons themsleves are reason for not working. Yesterday saw microwaves for sale in super market for $49!
Hope this helps.
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terry wrote:

I read it wrong, and didn't read the whole thing. I thought they were putting a 6 volt battery in series with the diode. Enough to get past the forward voltage drop of a high voltage diode.
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Bad diode is common cause. But you must know what you are doing because the hi voltage in a capacitor is deadly and can still be there after the diode has failed. WW
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WW, 1/15/2010,8:57:08 PM, wrote:

Considering it is over 10 years old and I have no drawings or parts list I assume it is not worth the effort.
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On Fri, 15 Jan 2010 21:42:08 -0500, "badgolferman"

Probably not. When my Amana model 2 Radarrange broke, about 20 years ago the parts woman suggested it was the microwave tube, about 250 dollars. When I called again, she (another she) suggested it was the diodes, about 125 dollars. When I actually took the thing apart, the insulation to the diodes was crumbling, and if I couldn't see arcing, I knew there had been some. This was the second model ever made and pretty old. I used some GE silicone to insulate it. I figured if they make glass out of silicon, the GE silicone must have a high dielectric value.
That worked for another 5 years and then the transformer went out. Again they wanted 375 but said he would give me the wholesale price of 250, dollars, for a replacement transformer. I said to him, you know I'm the last guy in America who's going to try to fix one of these? You know you can buy a new one that's nicer for about 100? Sell it to me for 50 so you can make a little money from your leftover parts.
He told me to write Iowa. I liked my prototype model, that looked just like the ones in history books, so I did. I told them to save 6 for their museum and the family of the inventor and owners, to keep theirs working, and sell the rest for what they could get. They wrote back and said to call a number in Pennsylvania. I called and it was like starting over again. He still wanted 250
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See: http://www.repairfaq.org/REPAIR/F_appfaq.html for good information on uwaves. You can probably find a wiring diagram on the inside of the metal uwave cover. Remove screws along the back and bottom to get the cover off. Read the FAQ carefully about electrical hazards. Then report here what you find and we can probably walk you thru some fairly simple checks. Do you have a voltmeter?
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hr(bob) snipped-for-privacy@att.net, 1/15/2010,11:48:43 PM, wrote:

Okay, I have done more troubleshooting of the microwave. There are three interlock switches on the door and they all open and close properly. There is a secondary interlock relay on the circuit board that 115 VAC is getting through. That is directly connected to the primary windings of the transformer and when I took both leads of the transformer I read the 115 VAC on the White & Black wires. Ohms checking of the primary and secondary windings are lower than what the schematic shows which are 49 and 89 ohms respectively, more like 20 ohms or so. The high voltage diode cannot be read either way and a replacement that someone gave me from their old oven reads the same way. I tried that one out and still get no heat. I put my multimeter on the capacitor on its highest ohms scale and get a wavering reading.
I do not think the interlocks or the diode are bad. The transformer and the capacitor are probably good but I defer to the experts here. I do not know how to check the magnetron. There are two round black components inline with the power that I assume are the flame and gas sensors. My guess is they are good since power is getting all the way to the transformer.
Any more ideas?
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wrote:

I used to troubleshoot these things with a fused "fool killer", connecting it directly to the primary of the transformer. This elininates a lot of the circuity in a hurry.
JImmie
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mm wrote:

Uh... silicone is nowhere near the same thing as silicon, or was that a joke?
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wrote:

It's what I thought at the time. I still don't know what the relationship is.
But it worked. I've successfully used GE silicone** for the micowave, and for a color tv flyback transformer where the voltage is about 30,000 iirc. (The second time I had to put on several layers. Each layer would move the spark somewhere else, and the final one stopped it.)
**(sealer or cement?)
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mm wrote:

There is no relationship between the two except they are both found on planet earth and they are spelled very similar. Silicone is man made and silicon is natural (I think silicon is the second most common element on earth). Seriously, it's about the same as comparing toothpaste to granite.

Glad it worked for you. I used it once on an old video game monitor to fix a high voltage leak also, (although I gave the guy no warranty and told him it was patched up, not fixed.) Careful with that high voltage, it does go that high, actually higher. Get zapped enough times and you may end up like me and you know you wouldn't like that! And the picture tube holds a charge like a big capacitor. Some will stay charged up for many months.
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wrote:

There's no silicon in silicone!!! I feel as if I caught my wife cheating on me. Sure, she never said she woudln't, but I assumed it.
Whew, you had me scared, but silicon is an essential ingredient in silicones. As well as H, C, and O, and other things like Cl at times.

What are you like?

Yeah, I know about all that stuff, but thanks for the warning. If I have to touch a CRT, I'm careful to discharge it first.
I did get what I think was a 2000 volt shock once. I don't know how. I was being careful. I didn't fall over or anything. I think my other hand was 3 feet away. Either fear or the shock itself sent me falling 6 feet back and I dislocated my shoulder for the first time in about 10 years.** Then it came out a lot, within a year there was a 4-day period that it came out 3 times. But I had already started looking for a doctor, and a month later I had it fixed and it hasn't been out in 32 years. I can't sleep on my belly with my arm over my head anymore, though.
So I too am trying hard to avoid a shock. I don't touch anything when I put the silicone on, let it dry for a day, and don't touch anything when the tv is on.
**(I had dislocated it about 8 times prior to that, but then I got a job that required hard work, and I guess my increased muscle tone held my arm in place.)
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On Fri, 15 Jan 2010 17:38:17 -0500, "badgolferman"

When I wanted a wiring diagram from Amana, I had to beg the woman and promise up and down that I knew what I was doing and wouldn't kill myself. It's bad that everything else seems to work. It means the problem is serious and probably beyond your or my skill.
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wrote:

Maybe someone replaced the Magnetron with a Cryrotron.
Sorry couldnt resist a bad joke.
Dead oven can be caused by a lot of things. There are numerous saftey circuit and interlocks. One of the first things a tech would do is bypass all of this and see i fit will come up. Should only be done by a qualified tech. The circuit is very simple consisting of a very simple power supply connected to a Magnetron. Everything else just turns the power supply off/on. This doesnt mean it is easy to troubleshoot and it is very unforgiving of stupid mistakes the consequences of may be death.
Jimmie
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Could just be a fuse. These fuses are not readily accessible, requiring removing the cabinet/shell. And, these fuses can be soldered in place. God forbid the end user is kept in mind.
--
EA



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Call GE to if if there is a secret recall on the unit . Mine stopped working and it was repaired at no charge. Not sure what model it is .

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badgolferman wrote the following:

find a new microwave with the same or slightly smaller dimensions. I had a to replace an old cabinet MW with one slightly smaller. I put an oak frame around it to hide the gaps.
--

Bill
In Hamptonburgh, NY
  Click to see the full signature.
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"Everything seems to work fine on it except for cooking" - what the heck else is there? A light? The clock? My opinion is that if the oven doesn't cook, it really doesn't matter what else does. Microwave ovens are generally not thought to be a DYI kind of appliance. In today's world it probably could cost more to repair than replace. Measure its size and head to Wal-Mart. They are bound to have one almost exactly the same size.
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You think a chinese fly by night microwave is a good idea?
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