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Can I repair my - noisy but cold - microwave oven?

Can I repair my - noisy but cold - microwave oven?

I have a GE JES738 700 Watt microwave oven that now makes a loud(er) sound when I try to heat something. The problem is that it no longer heats anything.

Asked by: Guest | Views: 80
Total answers/comments: 5
Guest [Entry]

"Tom Lamb

Rep: 229



Guest [Entry]

Over the years I have repaired several microwave ovens. All of them had the same symptom - more noise than usual and no heat. The high voltage circuit of these units is extremely simple comprising a large transformer, capacitor, diode and magnetron. Personally I have never seen a capacitor or a transformer fail so the diagnosis usually comes down to the diode or magnetron - about $10.00 or $50-$80 respectively. You do need to be extremely wary of the killer voltages when checking these units. As already mentioned disconnect the power cord and using a well-insulated screwdriver short out the terminals of the capacitor just in case. A magnetron can be checked with a standard test meter on the ohms range. First check the resistance between the two magnetron terminals (remove the wires first). The resistance should be very low - in the range of a few ohms. Next check the resistance between each terminal and the metal fins of the magnetron. The resistance here should be too high to measure (in essence an open circuit). If the magnetron passes both these tests then it is quite likely fine. A microwave diode can be open or short circuited. A short circuited diode creates noise and no heat and an open circuited diode creates no additional noise but also no heat. Testing the diode using a regular test meter is not usually successful because the testing voltage has to be quite high. I always have a spare good diode to substitute as they are quite cheap. I also concur with other readers that if a magnetron is suspected as the failure cause then it may be more cost-effective and safer to just buy a new one. However I repaired my own over the stove model by replacing a faulty magnetron for a quarter the cost of replacing the unit. Above all stay safe.
Guest [Entry]

"Wow, the ignorance expressed here is astounding. I can see why ""people"" are warned away from repairing their microwave.

A magnetron is not ""radioactive"", it emits nothing when not powered and it emits radio waves when powered, it is basically a form of ""radio tube"" and most emit the same freq. as your old cordless phone and wifi router, just a lot more energy, thus why a microwave can interfere with your old cordless phone or wifi. There is no ""nasty radiation"".

The only danger in a microwave is the HV capacitor which can kill you so learn how to safely discharge one, it is not hard if you have half a clue. All the ones I have ever dealt with self-discharged as designed but don't bet your life on it. When replacing any component inside make sure to route all wires as you found them. When replacing the magnetron (most can be purchased new for $30-$50) be sure the gasket (usually inc. with a new mag.) is in perfect shape and in place and that the mounting tabs/area is undamaged. If the mag. mount/area and the microwave in general is not bent/damaged then it won't be leaking any ""radiation"". If there is heavy arcing/burn damage around the mag. mount area this may be a cause for concern re leakage, on some models it is an easy repair, on other it is not and the amateur may want to stop at that point. Do not crush or break the old magnetron, some of the older ones can produce a dust from the ceramic insulator that is very harmful to breathe in.

As to quality, I have seen magnetron failures in one year old machines and the brand doesn't matter much, recent microwaves use magnetrons manufactured in one of two factories that supply most of the world and the standard/QC is not what it was 20 years ago. There are other factors leading to some machines failing more often like waveguide design issues (GE/Kenmore over the range models were infamous re this) but nothing the consumer or salesman will be able to know."
Guest [Entry]

"the biggest thing in the microwave is the magnetron tube. They do wear out over time making it less and less powerful. There are other things that can go wrong inside, basic troubleshooting of powersupplies etc can give you success.

It seems from your question that is suddenly died. have a look if there is a short inside, maybe an insect or similar has shorted some high voltage part = accounting for the extra noise and lack of performance."
Guest [Entry]

"If the unit is no longer heating food, then the cavity magnetron has gone bad. Probably not worth trying to get it fixed, as you should be able to get a 1000w or better oven for less the a repair shop would charge to fix this one. 700w is really pretty low power anymore. Fixing it yourself would be somewhat dangerous, due to the voltages required to generate the microwave energy - failing to make a connection and energizing the unit could cause a short or fire.

Were there any lightning storms around the time the microwave failed?"