I have a non-heating microwave oven that I just opened up. I tested the HV
diode and it seems to be acting as a good diode. The capacitor measures 1.0
4 uF and >30 MEG-ohm, so it should also be good. That leaves the Magnetron.
Is there a way to check the tube without powering it up with high voltage?
Any visual signs might indicate it's bad?
On Monday, December 30, 2013 7:01:46 AM UTC-6, panabiker wrote:
V diode and it seems to be acting as a good diode. The capacitor measures 1
.04 uF and >30 MEG-ohm, so it should also be good. That leaves the Magnetro
n. Is there a way to check the tube without powering it up with high voltag
e? Any visual signs might indicate it's bad?
check the fuse inline to the heating element.
Doesn't that also leave the transformer and wiring and connections and
whatever component(s) switch the HV/RF circuitry on? The diode and
capacitor may well be perfect but there are other things to consider. I
have experienced more seemingly-dead microwave ovens caused by defective
interlock switches than any other single cause.
On Monday, December 30, 2013 9:49:58 AM UTC-5, BenignBodger wrote:
HV diode and it seems to be acting as a good diode. The capacitor measures
1.04 uF and >30 MEG-ohm, so it should also be good. That leaves the Magnet
ron. Is there a way to check the tube without powering it up with high volt
age? Any visual signs might indicate it's bad?
Well, this MW oven had a slow dying over a couple of weeks. It started taki
ng longer to heat up things and getting louder when starting up to finally
only being able to heat a cup of water to lukewarm after 5 min. So I don't
think it's a switch/interlock type of problem. I also checked all microswit
ches in the interlock mechanism to make sure.
What do you mean by "getting louder"?
A shorted diode will cause a loud hum.
A microwave diode has a bunch of diodes in series.
If some short, you may not be able to tell with an ohm-meter.
You'd think the problem would cascade rapidly, but stuff happens.
You could check the filament for continuity.
But there's not much you can do about it.
If it's not bad connections, it's scrap.
I don't think I'd risk getting microwaved or electrocuted
for the low probability of being able to fix it.
That cap is a killer. Mine had been off for days.
I was smart enough to discharge the cap.
I wasn't smart enough to use a big resistor.
Ripped my hand on the cabinet when the resistor exploded.
On Monday, December 30, 2013 8:42:01 PM UTC-5, mike wrote:
I mean the humming noise is getting louder, especially during the first few
seconds of power-on, over the last few weeks.
I tested the diode using a variable current-limiting power supply. Its forw
ard voltage is around 6 volts when the current starts flowing. When reverse
biased, no current is detected up to -25 volt. I can't test high voltage b
ehavior at its operating condition though.
It's about 0.4 ohm.
Yes, it's time to buy a new one. This is a cheap, 14-year-old $120 microwav
e so it's not worth any money or effort to replace the magnetron. I was hop
ing for either a failed diode or the cap as the cause.
Thanks to all who chimed in, and have a happy New Year.
Yes, the OPost reminded me of those who read the computer codes on their cars and announce it's the MAP sensor or the CP
sensor, when the books all say "MAP sensor circuit" and "CP sensor circuit" Then they replace the sensor, etc even
though it might be working fine. When the codes said my MAP sensor circuit was bad, I pushed the MAP sensor onto the
connector harder and it worked fine for 3 days. After that I strapped the MAP sensor to the connector as tightly as I
could with one of those plastic ties (not twist ties of course) and it worked fine until I got rid of the car after 9
I am on a roll here. My big old 1999 Sharp microwave/convection oven
stopped a couple of days ago as I was doing some egg rolls for dinner. This
thing is huge and heavy and is mounted inside an eye-level cabinet but I
wrestled it out and put it on the table to check for troubles. Guess what?
It was a failure of the secondary interlock switch. I think that when this
beast fails permanently I'll replace it with something similar and I'll
order a complete set of interlock switches at the same time and tape them
inside the case. BTW: RepairClinic had the OEM switch for just a few dollars.
It would need to be a pretty fancy MW to bother replacing the magnetron.
The last time I looked up a replacement it was over $70 which gets you
well into new MW territory. I assume you have checked the inline fuse
where the power cord comes in the unit. This means that the lights come
on and it all pretends to work, just not making things hot. Test the
door lock microswitces and the flame/heat sensor(s). If they all check
good, junk it. I don't know any test for the magnetron, but when you
junk it, there are a couple of really nice strong magnets you can dig
out of it.. There are lots of DIY projects you can mess with using the
transformer. Exercise due care around the capacitor. I always thought
the door was some type of glass, I was really surprised to find the door
is a finely perforated steel sheet (I'd love to know how they punch the
holes) with a thin piece of plastic on each face. Not much else worth
keeping. The glass dish is great for a serving tray/dish and the
turntable motor is about $20 if you have to buy one and they seem to be
about the same, I've been able to fix a few for others. Yes, I've
My 2 cents.
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