GE Microwave JVM1540DM3WW Everything but Heat

Everything operates correctly, except no heat. I can hear a transformer hum, come and go while it acts like it is working, like it is trying to run, but nothing heats. I understand electrical systems and have read considerable about troubleshooting and repair. I just wanted to ask before undertaking this task. Based on the circumstances with the on and off hum, what do you think?

** Do NOT even dream of fixing your own microwave oven.

The devices are ABSOLUTELY LETHAL !!

.... Phil

come and go while it acts like it is working, like it is trying to run, but nothing heats. I understand electrical systems and have read considerable about troubleshooting and repair. I just wanted to ask before undertaking this task. Based on the circumstances with the on and off hum, what do you think?

Bad triac?

Microwave ovens have a vacuum tube. If you have a bad tube, or no filament power, the transformer will hum and no heat is produced. New microwave ovens aren't a lot more expensive than new tubes and the labor to put 'em in.

come and go while it acts like it is working, like it is trying to run, but nothing heats. I understand electrical systems and have read considerable about troubleshooting and repair. I just wanted to ask before undertaking this task. Based on the circumstances with the on and off hum, what do you think?

Could be a bad heater in the magnetron, or the HV doubler is bad.

I'd not suggest opening a microwave oven for repairs unless you are familiar with handling the high voltage cap in them. They seem to be the perfect rating to electrocute folks.

If you're past that, and know how to dischard the filter cap, turn on the oven and check the HV output of the doubler, it should be around 4kV.

If that's good, check the heater coil of the magnetron, it should appear to be a short. Check the filament winding on the transformer too. It's more likely to have bad crimp connections than being burned out, but you never know.

A fairly detailed (even overly detailed) microwave oven FAQ is here

Anyways, if the cap or rectifier are bad, it's worth $15 and a trip to ebay for replacements. They're all pretty generic and the chinese junk off there is no worse than they build new microwaves with anyways.

If anything else is bad, it's just not worth fixing unless you want to make a project out of it.

"Tom Kupp"

*** If the unit had a faulty triac ( most use relays ) then the transformer would either:

1. Not hum at all.

1. Blow the supply use immediately.

... Phil

I promised to count the number of screws on my old (1981) samsung microwave oven. This was back when they were overbuilt. There's actually

20 stainless torx screws in the front door inner bezel just to hold the glass in place. It's amazing.

Could their purpose have been to hold the screen so firmly in place that it could not come loose and permit leakage?

the screen is behind the glass, or sheets of glass, where would it even slip or go? It's not like 20 screws will hold a piece of glass all that much flatter than 10. I've seen autoclaves with wimpier doors.

Has anybody ever come across a microwave oven that actually has microwave leakage out the front door or gaskets? We always did the testing, but never had a reject or a loose door.

Could the /glass/ slip?

The question is /plausible/ in the context that Samsung wouldn't waste time and money installing screws it didn't think were necessary. (See following.)

Back in the 70s (I think) the Government set emissions standards. I remember an Amana commercial (I'm watching "Perry Mason" as I write this -- why couldn't Barbara Hale have been my mother? Of course, then I would have been William Katt.) in which a large, sharp-edged weight was slammed against the oven, leaving a huge gash. Amana claimed that, even with this damage, the oven still met emissions specs.

I'd love to see what a large wedge would do to a modern microwave oven, other than go right though the entire thing, like a cup of to-go soup when the lids comes loose and it just instantly dissolves the paper bag you were holding just seconds earlier.

If there were strict standards back then, I doubt anbody is testing them anymore. Those cone shaped Simpson probes were the rage, then there were the taiwanese cheapo VU meter attached to a diode and a loop of wire leakage meters. Again, I've never seen any of them ever register anything.

Even the Amana and Tappan units didn't have thousands of screws holding them together. I've always been really curious about how this oven was designed or who it was copied from in the first place.

I have a near-end-of-American-manufacture LItton that's built like a tank. Haven't used it in a few years, but it'll still be working when I'm dead. Only problem is that the cavity's on the small side.

It's possible all those screws were needed to compensate for sloppy tolerances. But without tearing it apart, there's no way to know.

Not many people have a meter fit for measuring 4kV, and its pretty dangerous even for someone experienced with repairing microwaves!

The transformer secondary feeds 2kVAC to the doubler at enough current to easily guarantee lethality, and even when its switched off there's a hefty capacitor can give you a nasty belt!

I've heard tell of an apprentice left mucking about drawing sparks with the tip of a screwdriver while his boss went out to the van for a part - when the boss returned the apprentice was laying dead on the floor - the screwdriver had a cracked handle!

As for the fault with the transformer humming but not much else, the magnetron tube can lose emission (especially if you defrost a lot) or the heater can go O/C.

IWHT any bad crimps around the secondary side would arc noisily - but not in the low voltage heater circuit (be sure to discharge the capacitor before delving in to investigate!).

With the cost of parts & labour these days compared to what new ones cost, it may not be worth throwing good money after bad! I have the advantage of living in a block of flats, where a microwave gets left in the bin room every so often - if I don't need a replacement I simply strip it for spares. That way I have a selection of magnetrons with the various flange configurations.

A slightly odd one came in when I used to repair the things - the fuse had blown, and a replacement had it going again like nothing had happened, the usual inspection of the interlock micrswitches showed nothing amis (they sometimes weld intermittently if the user slams the door a lot) Eventually I discovered a "pimple" on the capacitor casing - obviously a minor explosion had occurred between the layers of foil in the capacitor and the flying debris had dented the can, apparently the capacitor had "self-healed" and was ready to go once a new fuse had been fitted. Playing safe; I replaced the capacitor before wrapping up the job.

I liked the ones that opened like oven doors. The last tappan around here died when the mechanical timer wore out.

Interesting point. Maybe the glass is what holds the door together.

I'm going to have to take the thing apart. The thing is guest-proof too. It's digital but you have to enter cooking times in this format

[time button] [enter the time] [time button] then [start]

it may be built around a soviet RPL calculator chipset.

It sounds as if whoever wrote the code didn't want to have to keep a running calculation of the number of seconds -- just do it once with the second [time button] press. Of course, it could have been done at [start] just as well.

The GE Jet in my range hood has a simple and easily understood entry system. I'm amazed how many microwave ovens have confusing and complex systems.

Couldn't aggree more. When my mehanical timer microwave went a few years back I went around to the 4 or 5 different microwave ovens at work to find the one that was simplest to use, then bought a very similiar one of the same brand. Key in time, hit start.

Jerry

nning

[time

ll.

stem.

But you're robbing the design engineers the opportunity to demonstrate how complicated a system they can design just to heat a bowl of soup.

Ian Field skrev den 05/04/2013:

Another thing to consider is the resulting effect of the microwave.

Using these formulas:

1 Ws = 1J

4.184 J for the temperature of one gram of water to increase 1 degree celsius (°C).

Then take the time for 100g=1dl tap-water to boil from tap-temperature, perhaps 10C, it is easy to calculate the resulting effect.

(And here you see the advangage of using metric, instead of units based on the length of king X's thumb and the volume of his bladder or whatever :-) )

Doing that, I discovered my microwave, labeled 900w, actually delivered

250w.

I don't know if it still takes 900w from the mains, but I discarded it and replaced it.

technically, you might have called it "working" :-)

Leif

--
Husk kørelys bagpå, hvis din bilfabrikant har taget den idiotiske  
beslutning at undlade det.

"Arfa Daily"

** Correct.

A couple of things will tend to under rate the actual heat power delivered by a microwave oven tested with a vessel of water.

1. An unsuitable vessel can absorb much of the energy.

1. Heat is lost to the surrounding air during the test.

2. The thermometer will usually under read the actual temperature rise.

So, use at least half a litre of water in a thin walled plastic container and heat the water to no more than 60 degrees C.

Be damn quick with the thermometer and even then allow 10% for losses.

.... Phil

I have a working Frigidaire microwave that was manufactured in 1983. The specs say 1.38 KW 120V 60HZ, a little odd, now it would be amps not KW. Don't know about the output power, nothing on the unit, and the owners manual says nothing about the power. The model number is MC800M, I would think 800W is to low for the output power. But, I'm curious what is the efficiency of a magnetron? Mikek

PS. The owners manual says " If you move or sell the microwave to another person please report the change so we can update our records. Hope I'm not in trouble, I've moved 5 times without reporting. :-)