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Why is my microwave humming and not heating?

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My GE Profile Spacemaker 2.0 started to hum a bit louder and now makes no heat. I followed the GE troubleshooting flow-chart and it points to the magnetron, but the resistance checks (continuity pin-to-pin, open pins-to-case & no sign of any arcing or cracks in magnets). The HVT (hi volt Xfmr), Cap (capacitor) Xfmr, and diode all seem to be okay although my cheaper DVOM shows diode open both ways .. so I used 12v battery with 1.8k resistor in series & get 3.1v one way and 4.3v in other. The new diode that came with a new magnetron had same readings but this magetron was returned .. was wrong # and mounting pattern. So .. my unit draws about 5amps when mag is connected and about 8amps when mag is disconnected. Why more amperage when magnetron isn't connected ? Does this mean anything to anyone ? What should I do next ? I appreciate any help, thanks.

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It seems like your diode is bad. You say your cheaper DMM reads the diode as open in both directions, and then say it passes voltage in both directions. These are two opposite scenarios, but either is a bad diode. You should have continuity (i.e. closed) in only one direction. If you have continuity in both directions the diode is shorted, and is defective. If the diode does not have continuity in either direction it is open, and is defective.

Plus, your battery test should only pass voltage in one direction - the other direction should be 0.0 VDC. Replace the diode and see if this solves your problem.

Here is a site that explains the process. https://www.partselect.com/Microwave+tes...

Update 5/14/18:

Given that the 9v test measured voltage in one direction but not the other, indicates your diode is good. The voltage drop of the diode is most likely too great for your DMM to take a measurement. You component test chart even states, "Some inexpensive [meters] may indicate infinite resistance in both directions." So accept the 9v test.

So now I'm assuming your question is that even though the troubleshooting flow chart is recommending you replace the magnetron, your individual test of the component checks out good, so which is it. Most likely you have a short in the magentron (causing the humming). Try this: when measuring filament to chassis, tap on the magnetron to see if you can get it to show an intermittent short. The other explanation is the short happens only when the filament heats up during operation, but you don't want to test a live magentron.

You have already performed all the tests you can on the diode, HVC and HVT. They could still be bad (like a short between the windings of the secondary), but you do not have a accurate way of measuring them. The other check you can do is the wiring in the high voltage circuit. Check for burnt terminals, discolored wires, etc. Otherwise, I would replace the magnetron first, and see if this solves the problem. If not, next replace the HVC and diode. If this still doesn't solve the problem, replace the HVT.

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Thanks You Tim .. I will certainly try this .. especially since it's the most inexpensive part :) What troubles me is that another random diode that was supplied with the (wrong) magnetron tested the exact same way. Maybe it too was bad .. seems odd tho.

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Agree that’s it’s odd. By definition a diode passes current only in one direction (unless it’s a zener but we won’t go there), so double check your test setup.

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I took the diode out and it does not pass the resistance checks on your link. I tried 20k, 200k, 2000k, and 20m scales and it's open in both directions on all of of them. I'm not sure if I should disregard this due to my cheapo meter .. per my attachment because .. when I put a 9v battery in series with diode .. it passes 5.6-to-5.8 volts in one direction and zero (0) in the other. Battery alone reads 9.2v. The diode looks fine .. no sign of any blistering or overheating, etc. Any thoughts .. anyone ? I 'm also still baffled that the unit draws more amperage with magnetron un-plugged (8a) than connected (5a).

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I did put the unit back in place (over the range) and order a diode so I'll try that first (once I receive). If/when that doesn't work I'll take is back down & apart and further troubleshoot magnetron as you suggest. I thought the interior space available for the internals was generous enough to preclude a short, but your test seems logical. I'm still concerned about transformer too. I get approx 129 ohms from white wire (from HVC and per the flow-chart)) to ground and minimal resistances elsewhere thru primary and thru secondary. Schematic shows .3 on primary and 69 on secondary. Also as I said before, when I un-plug the mag .. the unit draws more amperage (8a) then when it's connected. I still can't wrap my brain around that. Appreciate any/all help. Thanks, Ron

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I replaced diode, NG. Finally got new magnetron and that did the trick, worked good, one time, then my touch screen stopped responding again (did this once before, then started working again). Old magnetron showed no indications when tapping and reading pin-to-case. Must be failing under load (as you suggested). It looks perfect too .. weird. Any thoughts for touch screen ? Appreciate it, Ron

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Hi,

Check th HV cap anyway, some have an internal diode and they tend to short completely sometimes.

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The cap term-to-term momentarily shows some ohmage, then goes open. Both terms to case are open. I think it odd that GE's troubleshooting points to replace magnetron vs further checking of the Magnetron. I'll try to add photo of troubleshooting chart (was inside unit).

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i would check your hv cap.

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My GE hv diode measures open both ways in diode mode fluke 76

the oven buzzes an unusually loud audible 60 hz so i stopped usage

web says replace diode part GE WB27X1160 so ordered online

do you think the magnetron tube is the culprit?

the model JNM7196SK3SS built March 2019

the needle nosed pliers handle grips coated still allowed capacitor dc stored charge to jump into me empty as a float so an insignificant amount of current to equalize i zing ed me - so i sleeved on tygon hose to insulate objective short out capacitor

Update (10/22/2022)

Can tube fail factory fresh using only 2years?

Update (11/26/2022)

Maybe the engg design to overly protect personnel from electrocution & irradiation burn incorporates sequential & coincidence interlocks that actually promotes failure by interlock (s) breakdown - the utility line power is intentionally cutoff from these parts creating oven irradiate whenever interlock(s) coincident are violated

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Hi @arouse,

The interlocks usually burn out due to people not turning off the microwave correctly, by using the control panel to either pause it or to turn it off, but by simply opening the door every time to stop it.

This stops the oven in its tracks as it's a safety feature to prevent harmful microwave radiation from escaping the oven cavity, but it also causes a flash across the interlock switches that open when the door is opened and the oven was still operating at the time and eventually the contacts burn out.

The safest way to discharge the HV capacitor is to connect a 10M Ohm 10W resistor lead (alligator clip - resistor - lead - alligator clip), between the HV capacitor +ve terminal and the chassis of the oven

This will fully discharge the capacitor after a couple of minutes but most people can't be bothered to wait that long and short it out - sometimes with disastrous results. I've seen incorrectly sized pliers welded across the capacitor terminals when people tried shorting it out using them

Good thing that the capacitors are fairly rugged as directly shorting them out whilst they are still fully charged can also sometimes damage it as well, so they get away with it mostly. The HV capacitor can store >5000V DC for months, even if the power has been disconnected from the oven for this length of time

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That's exactly how i finnagle cooking ops yanking open door still irradiating so this logic transient puts intense immense step function change unto the interlock system integral

Dang gotta remv logicboard

Test the interlock discretes notwithstanding interlocking repetition violations as in yanking door open to cease irradiate

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221127Sunday

it's fixed

30 sec hi power

16fluid oz water bowl irradiate proof

burnt my index finger tip not boiling

Superheat?

wallah hip hip hooray

utter silence now irradiating water molecules fat molecules flesh molecules vege molecules

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Sorry I don't know how to assess your capacitor behavior. Mine was also weird as you may have read. I never did learn if those odd readings were due to my cheapo meter or what. Be careful !

Replacing the magnetron definitely solved my problem and she continues to work fine today 4+ years later. It was a bit of a chore since mine is over stove / under cabinets. I hope you have similar positive results. I think that's the culprit when you hear the loud buzzing - yes. G'luck, Ron

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You know my dorm is floated over ground so when my datum touched the cap with vinyl dip & grip insulate too measly, the six thousand with microampere raised my charge datum upwards, but i am floated, like bird perching hv lines, a tiny zing is sensated, charge leaking thru dip&grip insulate equalizing both sides, cap & me - stand on earthing would mean death - bless the floated human on insulate linoleum thick

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Ron C will be eternally grateful.
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