GE PEB7227BL1TS Microwave Oven Won't Heat

[Fran D]

As the title states, I have a GE PEB7227BL1TS Microwave Oven that out of the blue will no longer heat any food. Every button works, the fan runs, the turntable turns, but nothing gets hot. No indication of failure beforehand, i.e., smells, sounds, flashes, etc. Any idea of what I am dealing with? Google search indicates either the HV cap or transformer, but only the latter if there were burning smells. Any guidance is appreciated.

[MrApplianceMatt]

Check all your door switches and the latch body (switch holder.) The latch body can wear and prevent the 3 door switches from actuating correctly. Microwaves are probably the most dangerous appliance in the home to work on if you're not careful. There's a development where I live whose contractor put these in all the new homes and the most common reasons for the unit not functioning are either the door switches/latch body, the capacitor, diode/rectifier, and the magnetron. The mica waveguide cover will absorb oils and food over time and can become an arc point that can damage the magnetron antenna. The magnetron would have to be removed to be visually inspected for damage. I would recommend calling a professional if your electronics experience is limited.

[Fran D]

Thanks for the info. Door switches are fine, but the diode definitely tests open. Don't have a large enough scale on DMM to check shunt resistor in cap (10 M). The cap, visually, looks good; no bulging or leaking at the case seams. I have an LCR meter at work that I can use to check it. 

Everything else, visually, looks good in the cabinet. No burned or discolored parts and no smells. Hopefully, the diode is it.

[ServiceTech_Daniel]

When you run it can you hear the magnetron? Check for 120 vac at the primary windings of the transformer. If you don't have 120 vac then your problem lies somewhere at the controls/door switchs. If you do have 120 vac at the primary winding then your problem will be somewhere in the High Voltage side (transformer,cap,diode,magnetron)

how did you measure the diode? 

 

[Vance R]

Before you get to involved in checking stuff. Put 1 cup of water in the microwave, measure the amperage draw while running a test cycle for 3 minutes.  Let us know the results.

[Fran D]

Thanks, gentlemen, for some reason, I'm not getting the email alerts for your replies even though I'm subscribed.

Anyway, you're suggestions were good, but after testing the cap good and the diode open, I replaced the diode with NOS. It's back up and heating. Hopefully, it sticks.

Thanks for all the help.

[Fran D]

So....it worked for three days. Cooked everything normally as before, no problems. I wasn't home when it stopped working, but it is back to not heating.

I haven't pulled it apart yet, but I can check to see if I can find my line splitter to do a current measurement. I'll report back any values.

To get back to Dan's earlier questions, previously I could hear the magnetron running and still do as the tone changes for different heating cycles (i.e., defrost, et al). I didn't measure the transformer voltage. I spent the time looking for opens/shorts in the door switches and diode. I used the diode tester on my DMM (9V) to determine if it was open.

Back to wrestling it out of its cabinet (it's knee-level in an island, so yeah, back issues).

[Fran D]

OK, finally got around to this.

Following Vance's suggestion, ran a 3 minute HIGH cycle while measuring the current. It started out around 6.6 A, bobbled around that and 6.4, before finally settling to about 6 A just before the end of the cycle. The water did not heat.

Conclusions?

[Vance R]

Between 3 to 9 amps -  HV issue, HV transformer ok check capacitor, diode, magnetron

[Fran D]

Vance, just to make sure that I understand what you are saying, you are stating that there is a HV issue, but the HV transformer is OK? The only parts to check are the diode, cap, and mag?

[Vance R]

correct

[Fran D]

OK, just starting with the mag, I have about 0.5 ohms across the filament. There is no short from the filament to the case. However, it does seem that one side of the connector is a little burnt. It still conducts (< 0.5 ohms), so maybe just normal wear and tear?

I don't have my professional meter with me, so I used the 9V battery in series with the diode to test it. It doesn't conduct in one direction, but I drop about 4.5V in the other. The battery is fully 9V. Is the diode drop expected to be 4.5V?

When I check the capacitor with the multimeter (don't have the LCR on me ...great planning, huh?), after fully discharging, placing the leads across the capacitor with the meter setting at 2MOhm, the reading will start at zero and climb to open in both directions. It measures open in both directions on the other resistance scales. There is a 10 MOhm shunt resistor in the cap, so the 2MOhm scale probably slowed things done enough to see the cap charge. Nevertheless, it seems to be behaving like a cap.

Anything that I have missed and/or misinterpreted?

[Vance R]

13 minutes ago, Fran D said:

However, it does seem that one side of the connector is a little burnt.

This could be your issue.

[Fran D]

OK, so everything else checks out? The 4.5V drop isn't unexpected? I'm used to low-voltage Si diodes where the drop is 0.7V.

[Vance R]

HV diodes are different can't use just a dvm. Have to use a 9 v battery and dvm, range is 3.5 to 6 is ok.

[Fran D]

OK, thanks.

[Fran D]

I'm trying to figure out how the connector can be the issue. When I reassemble it back into the circuit, I get good continuity from the wire to the cap and across the mag. Is the thinking that somehow it was disconnected before?

Also, just for S&G, I was testing some of the circuit values specified in the sheet inside the cabinet. It states that the primary side of the transformer should be 0.3 +/- 10% Ohms. I'm measuring 0.8.

[Budget Appliance Repair]

The MagTube is one thing that can check out OK with no shorts to ground and the filament reading the correct OHMS and can still be bad.

Eliminating all other problems then it will be a bad MagTube.

[Vance R]

I'd start with simple stuff first replace the slightly burnt connector. If that doesn't work then move on to replacing the mag tube as @Budget Appliance Repairsuggested.