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Microwave oven troubleshooting

We got this oven in for repair Its a GE model JE2160SF-03. The name plate reads 120V 1.65KW (MW). I don't know what the MW stands for however the 1,65 KW would seem to translate into 13.75A. The line fuse is 20A. The customer tried to use this with a generator during a recent power failure. He said that the microwave made some odd noises as the generator surged a few times and so he disconnected it.

On full power mode the unit draws about 7.0 amps and does not heat the food. An ohm meter test on the capacitor seems to indicate that it has a good bleeder and that it does charge. I ran the transformer primary at 12 volts, (10 percent line voltage), and noted that it puts out about 260V between chassis and the HV lead. There was a small voltage present on the filament terminals as well. There are no shorts or leakage to ground on any components. The diode tests good as well. With a 10 ohm resistor in series with the diode during full power mode the voltage drop according to Sam's notes should be between 3 and 4 volts. The reading I got was about .200V.

During brief tests of the unit the Magnetron seems to get ever so slightly warm so that is the only indication that something is getting to it. I haven't tried to make any HV measurements. I really don't have a safe way to do that. I'm ready to condemn the Magnetron however I would hate to think that I'm overlooking anything. Does it seem possible that power surges might harm only a Magnetron while at the same time spare all the delicate electronics? Does anyone have any further thoughts on this? Thanks, Lenny.

Reply to
klem kedidelhopper
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You could power the HV transformer from 12 VAC with it connected and see if you get several hundred V.

Check the magnetron filament. If it's possible to disconnect the HV from the filament winding, see if the filament lights up and the tube should get fairly warm from that alone.

Since you're only drawing 7 A - which could be the no load current for these very lossy transformers, it sounds like either the magnetron is bad and not drawing any current or its filament isn't lit.

Any shorted component would result in higher current.

But how running on a generator killed the magnetron might be a mystery.

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Reply to
Samuel M. Goldwasser

On Thu, 1 Apr 2010 12:18:38 -0700 (PDT), klem kedidelhopper put finger to keyboard and composed:

MicroWave???

- Franc Zabkar

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Reply to
Franc Zabkar

"klem kedidelhopper"

** Gotta be a leg pull ???

** OK - so the magnetron is not operating and you are seeing only the usual, rather high magnetising current for the transformer. Attempted use with a "generator" is the likely cause of the failure cos many small generators are voltage controlled but not frequency controlled.

The PSU in a typical microwave oven IS sensitive to the AC supply frequency - cos it is resonant at 60Hz (or 50 Hz as the case may be).

Operating at a higher or lower frequency then intended will cause serious misbehaviour of the PSU and in your example this has caused failure of the magnetron, likely by over-voltaging the heater.

.... Phil

Reply to
Phil Allison

use

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But the filament is not open. Lenny

Reply to
klem kedidelhopper

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