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

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On 12/19/2012 8:18 AM, The Daring Dufas wrote:

What you mentioned is irrelevant. All that matters is what the OP read and is gonna do.
discharging the capacitor through a 110k ohm

Since you asked for a critique on your method, here it is. Check my math. Using round numbers... 4000V / 110k is ~36ma. 36ma * 4000v is 145454 mw = 145WATTS peak. Half watt resistor. Methinks a metal film might vaporize before that cap discharged. Carbon might take the energy, if you can find one.
I'd suggest, from the experience level suggested by the tone of the OP, that your advice is more harmful than helpful.

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No need to worry about the power rating, a 1/2 watt resistor is only rated for less than 500 volts. When the resistor blows apart, the arc will finish discharging the capacitor.. Big grin..
The microwave is one place that if you do not have any idea what you are doing and how to do it safely , you beter keep your hands out of it or have a good insurance policy for your wife and kids to collect on. Once you pass about 1000 volts, many things that seem to be insulators are not.
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On 12/19/2012 5:44 PM, mike wrote:

I've probably dealt with a lot more high voltage sources than you have over the past four decades. I've never had a problem using a 100k resistor to discharge a cap in a microwave oven. The danger I would warn anyone about microwave ovens is to be careful not to expose yourself to the non-ionizing radiation from the output of an operating magnetron. Damage to the lens of the eye is quite possible. Of course, I've also been known to use The Jesus Method to discharge capacitors and find circuit breakers,........because it's fun. ^_^
TDD
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Me, too. As to circuit breakers, I did make a plug in breaker popper. I don't use it on FPE Stabloc panels. Ah ain' 'tupid, y'know.
Christopher A. Young Learn more about Jesus www.lds.org .
wrote in message
I've also been known to use The Jesus Method to discharge capacitors and find circuit breakers,........because it's fun. ^_^
TDD
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Your going to have to find the discharge time, capacitance, voltage, resistance. I don't see the cap value listed here. I'd be more inclined to use at least a 2 watt resistor, but I like sparks.
Greg
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On 12/19/2012 7:21 PM, gregz wrote:

I didn't say hold the freaking resistor in your hand. ^_^
TDD
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I see the diagram including bleeder resistor, and may have internal 10m bleeder, but might be external. I would not trust an internal resistor as being good.
Ok, a 1 uf cap and 110k resistor tc if .1 sec, so 80% of the voltage will disappear in .22 seconds. A half watt resistor could smoke.
Greg
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On Wed, 19 Dec 2012 15:44:03 -0800, mike wrote:

OK. I will read further before going to Radio Shack for that resistor. :)
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On Wed, 19 Dec 2012 10:18:05 -0600, The Daring Dufas wrote:

I have some resistors but they're the teeny tiny ones with stripes.
I will need to go to Radio Shack and get a roughly 100 ohm resistor that is a half watt or so first then.
I wonder though: Why wouldn't a screwdriver across the terminals work? (Assuming a non-conductive handle.)
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On 12/20/2012 4:30 PM, Danny D. wrote:

It will certainly discharge the cap. Don't use the tip, because it will make a divot in the blade. In theory, nothing happens. As a practical matter, it doesn't take a huge transient to take out the controller board. It's not likely, but why risk it.
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On 12/20/2012 6:30 PM, Danny D. wrote:

Shorting it with a screwdriver is similar to The Jesus Method where you shout JESUS! when the bright flash and boom melts the terminals and tip of your screwdriver. A hundred thousand ohm resistor may pop which is why you use insulated needle nose pliers and not your fingers to hold the resistor when you use it to discharge the capacitor. Resistors are cheaper than fingers. ^_^
TDD
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On Tue, 18 Dec 2012 20:55:20 -0700, Tony Hwang wrote:

Hmmm... I don't remember hearing buzzing but there is the loudness of the microwave sounding like it's working. The turntable and lights do what they should, as do the control.
The food just comes out cold.
I'm going to fully test that diode - and report back. I went to Fryes last night but they didn't have a single 13x22 inch microwave!
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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 www.lds.org .
wrote in message

That's the diode I saw in the pictures and the diagram. Diodes come in all shapes and sizes. ^_^
TDD
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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 www.lds.org .
On Mon, 17 Dec 2012 18:07:35 -0500, Stormin Mormon wrote:

Ah, there was something there.

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.
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On Mon, 17 Dec 2012 09:19:35 -0800, Smitty Two wrote:





I seriously doubt I'll be writing a lot on this as all I'm trying to do is make a good decision as to how to proceed.
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On 12/17/2012 11:04 AM, Danny D. wrote:

Looks like less than 2 feet to me. For something other than a fuse I'd just replace it.
FWIW: Panasonic makes a really good microwave. "Invertor" 1300W. But I think you need one that's insulated to protect it from the heat of the oven.
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I agree with Mike: use common sense and due caution. I've fixed many microwaves and never seen a dead magnetron. Diode [cheap] has been the most common failure. More irksome is a dead control panel. [I have a 30 year old Toshiba going strong with a sturdy dial timer.] I'd stay away from the Panasonic "inverter" models as there is no reason [unless you care about weight savings from not having a heavy transformer] to over-complicate these simple circuits with an inverter.

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On 12/17/2012 1:28 PM, John Keiser wrote:

Could be. I'm not sure what the inverter does. I've been using mine daily for over 7 years now. It does have quite a few options.

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On 12/17/2012 11:28 AM, John Keiser wrote:

I cheaped out when I replaced mine and didn't get an inverter. I regret that decision.
It has 3X the power of the old one. And the 15-second on-time is way too long for power regulation on small loads.
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On Mon, 17 Dec 2012 12:20:18 -0800, mike wrote:

I'm confused why an inverter is needed for an AC appliance.
I do see three voltage transformers though.

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