power mystery or appliance defective

[psala]

I was called to check the quality of a household circuit. Here is the problem homeowner has: About once every 2-3 weeks their above range microwave oven will just stop during heating operation and then clock on it needs to be reset. Then it works fine for a few weeks. The owner discovered that the symptom is the same as if you unplug and plug in microwave during operation, ie: microwave stops and clock needs to be reset. GE repair tells owner that problem is with homes power circuit.

I checked that all terminations are tight at the receptacle and at breaker in the panel. Also I verified that the microwave is on its own dedicated circuit and that the cable run from the receptacle to the panel is unbroken, ie: no junction boxes along the way. The microwqve breaker has never tripped. Wire is copper. When plugging in microwave, the plug goes in tight, it does not seem loose at all. The home was built around 1970 and the microwave circuit was added around 1990.

The microwave worked fine for me several times. I heated a cold container of water on high until it boiled. One odd thing that could just be a coincidence is that owner notice it only happens in the morning when it gets its first use of the day.

Is there something else I can test or do for debug?

 

[winnie]

You or your customer needs to determine if power is lost at the receptacle when the microwave goes out.

Because this is an intermittent problem, you likely cannot sit around and wait for it to occur. I'd recommend some sort of monitor that you can install so that your customer can get the information when a failure actually occurs.

I'd actually recommend a 'DIY' solution for this one: have your customer plug in something like a 'Kill-A-Watt' http://www.the-gadgeteer.com/review/kill_a_watt_electric_usage_monitor_review and simply tell you if there is voltage at the receptacle when the microwave dies.

A more 'professional' solution is for you to buy a plug in logger than will record these transient events, leave it plugged in for a few weeks until there is a failure, then examine the logs after a failure.

-Jon

 

[charlie b]

My question for the owner is this: When power goes out, what does the owner do to get it back on? What I mean is does the power go off and then on again, so that the microwave is ready to be used, and that it only needs to have the clock reset? Or does he (contrary to what you mentioned in your description), actually have to reset the breaker? Or does he unplug and then replug the microwave?

If it merely ?reboots,? meaning that it stops heating the food inside, and starts flashing the clock, then I would say the problem is in the microwave itself.

 

[psala]

>When power goes out, what does the owner do to get it back on?
Nothing; The owner does not have to do anything(other than reset the flashing clock) to get the microwave to work again. They do not have to unplug it or reset breaker.

>does the power go off and then on again, so that the microwave
>is ready to be used, and that it only needs to have the clock reset?
Yes.

My question for the owner is this: When power goes out, what does the owner do to get it back on? What I mean is does the power go off and then on again, so that the microwave is ready to be used, and that it only needs to have the clock reset? Or does he (contrary to what you mentioned in your description), actually have to reset the breaker? Or does he unplug and then replug the microwave?

If it merely ?reboots,? meaning that it stops heating the food inside, and starts flashing the clock, then I would say the problem is in the microwave itself.

 

[psala]

Jon,

Ah yes a logger sounds like a good idea! I suspect that if it is in fact the power and not the microwave, that there is not a complete loss of power, but rather just a dip in voltage that is enough to cause the microwave to "reset". If I can get my hands on a logger that will get me the resolution needed I will give it a try.

I would think it would happen more often, if it was the power though. One more item: I also tried to get the microwave to fail by turning on the elctric stove and toasteroven that are nearby but on seperate circuits, seeing if more load on the service had any effect, it did not. Owner did say it fails when nothing else is on in kitchen.

 

[jacobsond]

What model microwave is that? I am mostly a low voltage guy and also do appliance repair. I have in my shop now a jvm1650wh ge micro with the exact symptom.Intermitly the microwave will shut down during operation just like you have unpluged it. I have recreated the symptom in the shop but have yet to determine the cause.If its a GE micro I bet we have the same prob. Its likley an internal prob in the micro. Its very intermitnent and I am in the process of bypassing the 3 saftey thermostats and door switchs to find the prob.

 

[plate]

As others have said, you are trying to determine if there is a loss of power to the microwave or not. If there is never a complete loss of power to the microwave, then you can lean toward the microwave as the culprit.

How about a digital clock attached to the same receptacle. Set the clock, then if the microwave problem occurs, check the clock to see if it needs to be reset. If it does, then power was lost.

 

[al hildenbrand]

In lieu of a data logger, you might consider a simple clock/radio (sans backup battery) or other cord and plug connected clock.

Put a cube tap in the microwave receptacle, plug both the microwave and clock/radio in, set the clocks and wait.

 

[al hildenbrand]

:grin: -:HEH!:- :grin:

Great minds. . .

 

[plate]

Al, I was just looking for the smiley faces, you beat me!

 

[psala]

Similar model number: There's is: GE jvm1653bh Are you in VT? There's is currently in a repair shop in VT. BTW, customer had the smartcard(main computer-board) replaced, and symptom still occurred a week or two after. Let me know if you isolate the culprit, I can pass it onto customer And I will let you know what our culprit was, when and if we isolate it.

What model microwave is that? I am mostly a low voltage guy and also do appliance repair. I have in my shop now a jvm1650wh ge micro with the exact symptom.Intermitly the microwave will shut down during operation just like you have unpluged it. I have recreated the symptom in the shop but have yet to determine the cause.If its a GE micro I bet we have the same prob. Its likley an internal prob in the micro. Its very intermitnent and I am in the process of bypassing the 3 saftey thermostats and door switchs to find the prob.

 

[psala]

I like the clock idea, cheap too!! This got me thinking, like you guys said, if the clock needs a reset when the microwave does, then that points to the power. But could the microwave be defective in that sometimes it draws too much current or more than it's supposed to. Long enough to reset microwave but not long enough to trip breaker?? I know some appliances like dehumidifers have startup caps, I don't not if microwaves have them too.

As others have said, you are trying to determine if there is a loss of power to the microwave or not. If there is never a complete loss of power to the microwave, then you can lean toward the microwave as the culprit.

How about a digital clock attached to the same receptacle. Set the clock, then if the microwave problem occurs, check the clock to see if it needs to be reset. If it does, then power was lost.

 

[jacobsond]

board replaced 2 times by the appliance tech same symptom. I am the electronics guy so its my baby now. Ill keep you posted. It is the microwave in my case for sure. Finding the fault is going to be tough when it works normal 95% of the time.

 

[charlie b]

I still think the problem is with the microwave. I suggest that you suggest that the owner buy a new one (or borrow one for a month or two from someone), and see if the problem is still there.

 

[360Youth]

Sounds like the micro to me, too. If it hasn't already been mentioned, I would try plugging it into a different circuit and see what that does. don't know how much of in inconvenience, but it might be more cost effecient upfront.

 

[robbietan]

why not check the voltage variation at which the microwave can operate? probably there are times (plus the sag events) that the voltage can become too low for the microwave to operate.

 

[psala]

Hi jacobsond,
I sent you a privite message, take a look. Also my guess is that if the door opens during operation, that would not casue the symptom we see. I am not sure about the safety thermostats, are you able to trip one during operation, does it produce same symptom? Let me know what you turn up. The appliance repair guy has come up with some best guess parts to replace. (since it's covered under extended warrenty, it's worth a shot for owner).

What model microwave is that? I am mostly a low voltage guy and also do appliance repair. I have in my shop now a jvm1650wh ge micro with the exact symptom.Intermitly the microwave will shut down during operation just like you have unpluged it. I have recreated the symptom in the shop but have yet to determine the cause.If its a GE micro I bet we have the same prob. Its likley an internal prob in the micro. Its very intermitnent and I am in the process of bypassing the 3 saftey thermostats and door switchs to find the prob.

 

[jacobsond]

talked to ge tech. leakage from the magnatron will scramble the microprosser on the board and cause shutdown. So you customer needs an appliance guy. If the product is less than 5yrs old warranty if more time for a new micro

 

[LHarrington]

Check the door switches they tend to get loose over the years of slaming the door. Next move to the themo circuit. Sound to be more like the micro than anything else.

 

[psala]

Great Jacobsonb!!

The microwave is less than 5yrs old. So I will suggest to have the appliance repair guy replace the magnatron, which will elimante the leakage issue that scambles the microprocessor.

Question: Does the MicroProcessor have to be replaced too? Did the leakage cause any permanant damage to the MP, or does it just temporarily confuse the MP. My guess would be that no permanant damage occurred since microwave currently works flawlessly 99% of the time even with leaking magnatron. What's your take?

Hmmm, why does the leaking magnatron only cause a problem 1% of the time, you would think either it leaks or it doesn't leak. But I digress....

talked to ge tech. leakage from the magnatron will scramble the microprosser on the board and cause shutdown. So you customer needs an appliance guy. If the product is less than 5yrs old warranty if more time for a new micro