PVM9179SF1SS - humming noise when door is closed, no noise when door is open

[swuser]

Model Number

PVM9179SF1SS

Brand

GE

Age

1-5 years

GE microwave, model PVM9179SF1SS. No power at all, so here is what I did so far.



1. Noticed one of the connector/terminal to the transformer's primary side was burned.
2. Checked thermal fuses, two of them circled in the attached image were burned out (checked with ohm meter, no continuity, right side on the bottom plate and on the magnetron). Replaced both and power was restored.
3. Now, when the door was open, microwave made continuous humming noise.
4. So I suspected transformer due to the burned mark on the primary terminal. Resistance across primary terminals was around 0.1 to 0, no shorts, resistance between body and secondary terminal was around 90 ohm. Thinking transformer was bad, I replaced that as well.
4. Still there was humming noise when door was open
5. Inspecting little closer, it appears that humming noise may be coming from the magnetron.

My next step was to replace magnetron, but I thought let me run it by here in this forum to get better and may be more definite idea of what may be wrong. I did not test the door switches yet since they are little hard to get to.

Any suggestion would be greatly appreciated.

Thanks

 

[Dan O.]

when the door was open, microwave made continuous humming noise.

Check the door switches.

 

[swuser]

Check the door switches.

Sorry about late response. I replaced whole door switch assembly (containing 3 switches), didn't help. I tested Mag again, there is 0.3 ohm resistance between terminals, terminals not shorted to ground. Diode tested fine as well.

Part # 115 in the diagram above, did die again, so I guess I'll have to replace that before I can try again. Not sure if this gives a clue. #115 was replaced but died again.

 

[Dan O.]

Part # 115 in the diagram above, did die again,

When did it fail? That is an over-temperature thermostat and should only open if it gets too hot, as a safety precaution.

I don't know why the magnetron tube would hum with the door open. NO power should be getting to any of the heating components (magnetron tube, HV transformer, diode, capacitor) when the door is open. The door switches are suppose to prevent that.

JMO

Dan O.

 

[swuser]

So sorry I got this reversed. Humming noise from Mag when Door is closed. Humming stops when Door is open.

 

[Dan O.]

Humming noise from Mag when Door is closed. Humming stops when Door is open.

If power is getting to the magnetron tube even before cooking is set on the control, the control may be malfunctioning.

That shouldn't however affect the over temp thermostat that you say keeps failing.

 

[swuser]

Here is the order of parts replacements:

1. no power to microwave. TCO #110 and #115 (see diagram) were burned out, replaced both
2. now, power was restored, but MAG started humming when door was closed, no humming with door open
3. thought HV transformer was bad, replaced. Didn't help, same humming sound when door closed
5. replaced whole door interconnect assembly (with 3 new switches), Didn't help, same humming sound when door closed
6. lost at this point. capacitor, diode, MAG all test out ok
7. checked TCOs at this point, noticed TCO #115 was burned out again

So, not sure at what point TCO burned out.. I would hate to keep buying that part if its going to keep burning out if something else causing the problem. For testing, can I just short TCO #115 terminals for testing or not a good idea?

I read somewhere that one of relays, may be RY2 ? could be bad. any idea on what I can check next?

Thanks a lot

 

[Dan O.]

but MAG started humming when door was closed,

The magnreton hums event WITHOUT the control being set to cook?

If the hum is coming from the magnetron tube, it has to be getting power. No power should get to ANY parts of the cooking system without cook being initiated on the control. It is the electronic control that switches power to the cooking system. The electronic control has relays on it that do the switching of power. Those relays are not usually available separately from the control.

LINK > PVM9179SF1SS Control WB27X10866


An overheat thermostat could be bypassed for testing purposes. It should not be left that way.

Make sure the microwave is not mounted too close to the stove top beneath and too large of pot wasn't being used on the stove which might have overheated the microwave and have tripped the protector. I don't know any other way that protector would trip.