Kenmore Microwave Oven goes belly up - twice in 2 years.

The way it is assembled is specificallly designed to make access difficult. There is a power supply inside of that unit capable of producing 4000 volts at a half an amp, which is guaranteed to kill you.

As if that wasn't enough, the capacitor can retain sufficient enough energy to cause a ventricular fibrillation long after the unit has been turned off and unplugged.

Microwave ovens are rather simple devices, but unless you have the specialized know-how in dealing with them, your life isn't worth it.

Jon

Fair and acceptable warnings to the complete idiot, but I believe you're lapsing into hysterical hyperbole. Electricity is *not* "guaranteed to kill you." It's only theoretically possible that you could die from opening up a microwave to fix it. If you do accidentally touch the wrong thing, it'll give you a shock, which will remind you which part not to touch.

Most of those theoretically dangerous parts are hidden away in secondary cages anyway. You can easily open up a microwave and fix it without having a panic attack.

Well "Smitty", I don't think your perspective of high voltage/high current appliances is a very practical one. Beyond that, suggesting that the innards of a microwave are anything less than lethal is beyond negligent, and I'd say foolhardy as well.

Jon

Well "Jon," I actually think my perspective is extremely practical. It's a perspective that allows things to be repaired. This (a.h.r.) is a DIY group, after all. If we were all terrified to repair things, not much would get done. All those "Danger, Will Robinson" labels that you see on things were penned by lawyers.

My GF and I recently repaired her microwave. We found a nice schematic and troubleshooting flowchart inside, and replaced a $20 thermal switch. Replacing the unit would have cost several hundred. Peanuts to a lawyer, but not to me.

Oh, yeah, I also stared death bravely in the face and got her TV working again last week, too. Another sinister appliance, with voltages just waiting to leap out and kill people in their sleep.

On Sun, 27 Sep 2009 12:16:33 -0700, Smitty Two put finger to keyboard and composed:

This may help.

Parts & Exploded Views:

Be careful of item 5000:

- Franc Zabkar

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Please remove one \'i\' from my address when replying by email.

el!retrieve.pd?mode...

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uwave ovens arent any more complex than a regular thermal oven. The magnetron requires a few thousand volts so you have a very simple high voltage power supply. You have a timer for on/off and you have a bunch of saftey switches that makes sure the door is closed.

Jimmie

I've been shocked numerous times by TV's and video monitor High Voltages, about 35,000 volts. Had it arc about an inch to my finger. Even worse was touching the case of the horizontal output transistor. That leaves a small burn and you get the aroma of burning skin. Please keep that in mind when I post something really stupid! ;-)

Years ago when I was very young and tubes were used as rectifiers in the flyback cages. I stood there and watched a man demonstrate how he fixed TV's found on the dump and various places, with tubes, also found in TV's. Any ways, as he pulled the tubes while the unit was on (operating) and replacing them on the fly, it was kind of funny when he reached inside the cage of the HV compartment to pull the rectifier tube.

I can say that this person is still alive today, and the sheet rock on that wall had to be repair later on.

Lesson learned. Make sure you have plenty of space between you and the wall, so not to create more damaging repairs! :)

If either of you had touched the HV of a powered microwave, you would not be posting here today. :( It may only be 3-5kV, bit it's capable of a good fraction of an AMP if not more.

Enough said.

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t

I agree with Jon. The innards of a microwave CAN be lethal. That doesn't mean any more than standing under car on a lift WILL be lethal! BTW I am a retired electronics and radio transmitter technician and manager! But it is very much the sense and capability of the d-i-yer that comes into play. e.g. I have one neighbour about whom every one shudders when he even looks at electrcity, no matter how often you try to teach him. He's the kind that says "Well can I put a screwdriver between there and chassis. My brother says that will test the high voltage !!!!!". He is dangerous with any voltage over 12 volts and he doesn't even understand that unless he can clearly see a broken off or corroded wire on his truck! Recently an acquaintance asked us to 'look at' his favourite microwave. He'd opened it and couldn't find the problem. He felt it could be the control board!!!!! My son, also a technician, and I fixed it in about 15 minutes on the kitchen table; a bad door micro-switch! The control board and the hi- voltage and magnetron circuit worked fine once we replaced the defective micro-switch (I have a jar of used ones salvaged from old m.waves). While working on it we defeated the hi voltage to the magnetron. For safety. When the owner had reassembled his m.wave he had not put the cover back on correctly and there was a potential leak on the right hand edge very close to the door opener and close to where one would put a hand to program or switch off! The 'edges' of the cover and the case were improperly meshed ............... Strewth; do wish people wouldn't touch stuff they don't understand! For example I know nothing about automatic transmissions so I would not 'go at' one. I'm also a very poor plasterer, so hands off. Everyone having fun? Within their capabilities.

I'm reporting you to SPCEP, or Society for Prevention of Cruelty to Exclaimation Points.

-- Christopher A. Young Learn more about Jesus

.

"stan" wrote in message news: snipped-for-privacy@31g2000vbf.googlegroups.com...

I agree with Jon. The innards of a microwave CAN be lethal. That doesn't mean any more than standing under car on a lift WILL be lethal! BTW I am a retired electronics and radio transmitter technician and manager! But it is very much the sense and capability of the d-i-yer that comes into play. e.g. I have one neighbour about whom every one shudders when he even looks at electrcity, no matter how often you try to teach him. He's the kind that says "Well can I put a screwdriver between there and chassis. My brother says that will test the high voltage !!!!!". He is dangerous with any voltage over 12 volts and he doesn't even understand that unless he can clearly see a broken off or corroded wire on his truck! Recently an acquaintance asked us to 'look at' his favourite microwave. He'd opened it and couldn't find the problem. He felt it could be the control board!!!!! My son, also a technician, and I fixed it in about 15 minutes on the kitchen table; a bad door micro-switch! The control board and the hi- voltage and magnetron circuit worked fine once we replaced the defective micro-switch (I have a jar of used ones salvaged from old m.waves). While working on it we defeated the hi voltage to the magnetron. For safety. When the owner had reassembled his m.wave he had not put the cover back on correctly and there was a potential leak on the right hand edge very close to the door opener and close to where one would put a hand to program or switch off! The 'edges' of the cover and the case were improperly meshed ............... Strewth; do wish people wouldn't touch stuff they don't understand! For example I know nothing about automatic transmissions so I would not 'go at' one. I'm also a very poor plasterer, so hands off. Everyone having fun? Within their capabilities.

I've repaired 5 or 6 microwave ovens and the problem was always a bad micro switch. Most of the bad switches were caused by a slip on wire connector making poor contact and getting hot, so I often soldered the wires to the new switch.

I guess you don't believe in learning, then.

The couple I've done, it's been the high voltage diode that goes.

-- Christopher A. Young Learn more about Jesus

.

I've repaired 5 or 6 microwave ovens and the problem was always a bad micro switch. Most of the bad switches were caused by a slip on wire connector making poor contact and getting hot, so I often soldered the wires to the new switch.

Interesting. Good idea though. We had a total of three or four m.waves in a school cafeteria we used to operate. With those and requests from friends and neighbours we had 2 or 3 bad magnetrons, which even used cost around $30 so unless you had one out of a scrapped unit hardly worth fixing! Couple of those over-heat switches (either little round bi-metal or occasioanlly solid state) that went open, Two IIRC bad micro switches, one bad diode and or capacitor can't recall which. Then also encrusted dirt, bad fan etc.

Well I sent them to you since I stock micro switches but no HV diodes.

Curious, what are the symptoms of a bad diode? I just thought about it, I suppose they (almost)never short out, and an open one may act as if the oven was working but nothing gets hot?

,

The diode is in a simple partial voltage doubling circuit. If it dud I think you'd get AC at reduced voltage on the magnetron? Probably not high enough to produce microwaves? In simple terms IIRC the HV capacitor (usually about 0.8 mfd.) charges up on one half cycle (60 hertz) and then discharges on the opposite half cycle in series with the already charged capacitor. Thus providing pulses of HV DC at approximately twice peak voltage of the transformer HV winding output. A recent bench test showed that one particular transformer had a 21:1 ratio. So with 115v RMS into the primary, the HV would be 2415 RMS and somewhere around 3400 volts peak. Double that minus some losses etc. we are looking at around 5000 volts DC. And unlike the HV in a colour TV which is a few milliamps or even microamps to a picture tube CRT, in a high impedance circuit, the power fed to a magnetron can be a quarter to half an amp or more; at around 5000 volts DC!!!!!!!! Anything from 750 to 1500 watts etc. Welcome to your own private electric chair; eh? Cheers.

No heat, loud hum. And, I sent you the ones with the bad microswitches, which I don't stock.

-- Christopher A. Young Learn more about Jesus

.

Well I sent them to you since I stock micro switches but no HV diodes.

Curious, what are the symptoms of a bad diode? I just thought about it, I suppose they (almost)never short out, and an open one may act as if the oven was working but nothing gets hot?