Microwave oven capacitor.. Dead short overnight?

[Frank]

Thanks. The new fan is cheap enough at around $30. I'm going to tackle this because when you cook a turkey or anything that takes a long time the fan noise drives you nuts.

[Rich256]

The megneto is a limited pulse. Doesn't quite approach what can be in a large capacitor. Both can hurt like hell.

I got "bit" just turning the flywheel by hand on a mower engine. Checking how close the magnets came. The plug wire was close to my hand. Just made me jump a bit.

I got my fingers across a 300 VDC source once. The current flowing from one finger to another. I had a hard time letting go. My army hurt for two weeks.

[maradcliff]

I bet that voltage made your voice go up a few octaves :) I wonder why they have such a high voltage? I may be wrong, but I think cars only have about 5KV to 10KV going to sparkplugs.

Similar to an electric fence. They are basically a capacitor discharge into a coil that puts out a pulse about the same as an ignition coil.

Thats good, then you knew the magneto was working. Thats how I always test them. The shock is minimal when you turn by hand compared to when the engine is running.

DC is much worse than AC. When I was a kid I had gotten an old tube type army radio transmitter. I got about 1000VDC shock, in addition to the RF coming from the unit. I was grounded to a metal microphone in my other hand. The chair under me was a heavy oak chair. After that jolt, I was sitting on the concrete floor about 20 feet away, the chair was flipped over and 10 feet from my bench, and the microphone was all the way across the basement, with the plug pulled out of it, and it hit my friend as it flew. My friend said I was walking around in a daze for at least a half hour, and I kept drinking water. He said I was not making sense, but I did pull the plug on that transmitter while stumbling around. I vividly remember this happening, but I still to this day find this void or memory loss for a short time. I think I darn near electricuted myself that time. I know I touched a tuning capacitor that was directly across the high voltage output of the power supply with a huge electrolytic cap right ahead of it. I grabbed it bare handed, and with that mic in my other hand, I got the full load. Additionally, I did not have a decent load on the antenna (like I should have), and got the full load of the RF too. This thing transmitted in the AM band, and used to knock everyones AM radio stations off the air. After several complaints from neighbors to my parents, my father took that thing away from me. Probably the best thing he ever did. Even though back then I was really mad at him. The electronics devices in the 1950's and 60's were far more dangerous than those made today. Today, most circuits are harmless, except for capacitor discharges, and of course the 120VAC line cord.

[maradcliff]

That sounds reasonable enough. If you are worried about that capacitor, leave the MW unplugged for a few days before you do the repair. They can still hold a charge though, but tend to drain off after a few days. Then just keep your hands away from parts other than the fan. You most likely have a bad bearing in the fan motor. Those small motors tend to do that. Your whole repair should be pretty simple. Be sure to put all the case screws back when you are done.

[maradcliff]

That's seems to be the most common part to fail. Microwave ovens are pretty simple. There really is not that much to them..... You probably have one of the first models ever made. Sharp seemed to make all of them back then.... My mother had a Sharp from that era. It finally died last year, and she bought a new MW and tossed that old one before I had a chance to tinker with it. She said it blew sparks and made smoke, and she was so freaked out that she called pulled the plug and ran over by the neighbor to have them call the fire department. The neighbor ran over and said there was no fire, so they did not call the fire dept. Mom is very old and tends to freak out from things like this. However, she did the right thing by unplugging it. I still hear about this "terrible fire" everytime I see her now !!!

[Rich256]

t him.

That is what I was brought up on. Put together my first Ham transmitter in the 40s. I remember something a professor stated in the mid 50s. It was something close to: "The transistor is an interesting laboratory novelty but will never achieve a useful purpose"

I worked with the first airborne digital computer. About 2000 peanut size tubes. Within four of five years we were upgrading to integrated circuits, bypassing discreet transistors.

The radar transmitter hat in the planes were the dangerous area. 30KV using tube diodes about the size of 1 lb coffee cans.. They lit up like big light bulbs so you knew to keep away.

In my life I got "hit" more times that I would like to say but was always really careful when working around those high voltages. Work with one hand and the other in the back of your belt was a safety procedure.

But not too many capacitors that will really hurt you. The string used in that transmitter were charged to 30KV and could hit pretty hard. Another I remember was about two feet square with a couple big balls sticking out. Even with a low voltage charge it could melt a screwdriver held across the terminals.

Reminds me of a guy working on an aircraft with a roll of solder in his hand. He got the solder between the 28 volts and ground the the solder melted in his hand.

[Doug Warner]

New cap was $15.00 Oven works perfectly now.

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