GE Spacemaker microwave shuts off after 15-30sec

[Petik]

Hi everyone! I have a 7yr old ge spacemaker JVM1861SF001 that was off for a couple of months (was out of the country) and when I came back the first time I tried it on it shut off about 20seconds into running. When it shut off it was as if the breaker blew. It went completely dead, but would come back if I unplugged and plugged it back in.

The interesting thing is that it will run no problem if I don't put anything inside it. It only shuts off when there's a "load" on it - a glass of water, for example.

I started doing some research and it seems that the magnetron is one of the most commonly failing parts. I called GE and since the microwave is less than 10yrs old, they sent me a replacement magnetron. I replaced it, but the symptoms did not change at all.

I then borrowed a nice Fluke multimeter from work with a capacitance meter. The main magnetron capacitor measures exactly what the spec on it says - 0.91uF. It also doesn't show any physical damage.

I then moved to measure the high voltage diode, which also didn't show any physical damage, and I measured 11 meg-ohms in one direction and an open in the other direction. Is this what I should expect? From what I read online, the reading across the diode should be between 50k-200kohm.

I tried measuring the motor capacitor with opens on both ends, but it doesn't show any damage and the fan works just fine - I assume that is what the motor cap is for.

So I think I'm left with either a bad transformer, a bad sensor on one of these parts or a bad control circuit board. Is there an easy way I can test the transformer and the sensors? Seems that the sensors for the most part would just have some spec resistance over them, but I can't seem to find this info.

I would greatly appreciate any pointers/advice. Thanks in advance!

[HayZee518]

a diode [albeit a rectifier] is supposed to conduct in one direction and act as an open in the other.

[Dan O.]

It went completely dead, but would come back if I unplugged and plugged it back in.

It would restart immediately after that routine? It didn't have to sit a while being off before starting again?

It only shuts off when there's a "load" on it - a glass of water, for example.

There should be nothing in most microwaves to detect whether there is a load inside or not. If anything, running without a load could cause the magnetron tube to overheat and cut out on an overload protector which (depending on the type of protector used) might reset once it had a chance to cool again.

BTW. It's not a good idea to run it without something inside to absorb the microwaves. Without a load they can be reflected right back to the magnetron tube damaging it.

JFYI

Dan O.
www.Appliance411.com
The Appliance Information Site
=D~~~~~~

[Petik]

It would restart immediately after that routine? It didn't have to sit a while being off before starting again?

It varied, at first it would have to stay disconnected for a short while. Now it just comes back within seconds. Sometime even just reopening the door wakes it back up.

There should be nothing in most microwaves to detect whether there is a load inside or not. If anything, running without a load could cause the magnetron tube to overheat and cut out on an overload protector which (depending on the type of protector used) might reset once it had a chance to cool again.

BTW. It's not a good idea to run it without something inside to absorb the microwaves. Without a load they can be reflected right back to the magnetron tube damaging it.

JFYI

Dan O.

So I found 4 thermostats/temperature sensors spread around the unit.

There is one near the transformer - this one reads very very high resistance across it when off. If i short the leads, the hood fan turns on and the rest of the unit won't power on - seems like a safety overheating feature. If I disconnect the leads to the sensor and leave them off, the unit won't power on.

Next is one directly on the magnetron. It reads very low resistance when off ~0.3ohms. If I short this one, the unit powers off in less than a second after turning it on. If i disconnect the leads, the unit won't power on.

There are two more sensors, one facing down near the control board - I assume this is to sense temperature below when cooking on the stovetop. Haven't tried anything on this one.

The last is directly above the cooking area of the microwave, didn't try anything here.

From what I tried here it seems that possibly the magnetron sensor may be the culprit, but the diode readings are puzzling as well. Any ideas?

Thanks.

[Petik]

went and played around with it some more. i found a very big resistor laying around, only 4ohm, but 25W so it could handle a lot of current if needed. I connected the magnetron thermostat leads to it instead of the thermostat. Now the microwave stays running no problem, but it doesn't heat! I tried a glass of water for 2 mins and nothing. It has a new magnetron it, it's not turning off anymore, what else could be broken?

[Psycho0124]

Are you sure the fan is operating in there while it's on? Also are you sure the air intake and exhaust vents are clean and unobstructed? A magnetron makes a LOT of heat while it's operating and will overheat in a matter of seconds without proper airflow. When a piece of electronics shuts off after a few seconds of operation, it sure sounds to me like an excess heat situation. Good luck!