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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. If it is something that I can fix, where would I find the parts? Is it a complicated or dangerous process to mess with the inside of a microwave? Should I pay a local repair service to fix it? Should I recycle the - just over a year old - appliance and purchase a new one?
Microwave ovens generate high voltages (thousands of volts) and dangerous amounts of radio-frequency radiation. Attempting to repair one is NOT for the amateur tinkerer. I advise recycling or trashing it and getting a new one (they don’t cost much these days.)
If you hear a very loud buzzing, it is probably a shorted high-voltge diode. This may be a small black stick wired to the high-voltage capacitor (metal can with two terminals), or could be inside the can. You would have to replace it. I doubt if the magnetron is bad, they are very reliable and last a long time. I designed microwave ovens for 30 years.
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.
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.
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.
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?
Some time ago mine (unbranded) stopped working too. I opened it and, to avoid the nasty radiation, I disconnected the cables that powered the transformer and magnetron. When I tested those cables for power (to see if they where delivering it when it was supposed to) it was intermittent, depending on the contacts position. Diagnostic: faulty contact leads. It could have been anywhere upstream the HV transformer and, therefore, fixable without messing the dangerous stuff (assuming you already have the proper respect for the 220V), but it was just a bad contact :) If nothing found there I would not have gone for the magnetron either… too risky.
I answered this question May 5, 2010, by agreeing with who I felt to be a “true professional,” (Tom Lamb - who said he designed them) based on my 40 years experience as a degreed electrical engineer and electronics technician. I didn’t call myself a “true professional” because anyone can claim it, even if they’re an idiot. And, I certainly didn’t want to sound like Brian Manuel or red. Brian Manuel, you say you have a degree? Were you unskilled at the time you took your engineering courses? Aren’t you glad your instructors didn’t have the attitude you display, in that they shouldn’t be giving advice to unskilled persons? I was one of those instructors, and of the thousands of unskilled I taught, I’ve never regretted the advice I gave. The purpose of this site is to give the unskilled access to professional information from people like me and Tom. And, Brian, if you don’t agree with its purpose, I agree that you should stop posting to this site, since your attitude shows you NOT to be a “true professional,” .
The economics really don’t work out for the average standard everyday $100 consumer counter top models. The only way it does is DIY. Salvaged magnetrons from scratch and dents or working machines that failed in another manner or units that were removed/replaced during remodel are available from some small appliance dealers for $10-$30. For commercial units or over the range models that cost a lot more to purchase the economics can work out. New magnetrons can be purchased for most consumer models for $40 - $50. A lot of the postings here are people inquiring about OTR microwaves. Other situations where people repair is if they have an odd size / built in or top of the line (maybe + convection oven) models.
We have a Magic Chef, two years old, that still heats OK, but makes a lot of extra noise. It is easy enough to open up, and I did discharge the high voltage capacitor, and remove the high voltage diode, so I could test it. The diode is good, the wiring looks good, and I can’t find anything wrong with the fan or the turntable drive. I am reasonably sure that the magnetron is the source of the problem, but the economics of repair don’t work out in this situation. A new, similar microwave oven sells for about 100 dollars. There is a nearby appliance service company, that does not have a fixed base, they only want to send out a service tech to our house, and the minimum service charge is 45 dollars. Add in the cost for parts and labor, and it makes no sense to repair this unit. I am wondering how anybody can make any money selling a new microwave oven for 100 dollars.
Maybe something burst from the microwave like a light bulb or a circuit popped? If you feel like it is working fine otherwise you should concerned with local repair person except to mess with it.
