Whirlpool Oven/Microwave board repair

I get black red white gold or 2.9 ohms, probably 2 W metal oxide as my first guess. These resistors totally open and act like a fuse. But 2.9isn't a valid resistor value, so re-thinking....

Actually, my BEST guess is 392 1%
some color - white(9) - Red(2) and black is 1%
Is the unknown color orange?
The Black band is spaced further away which makes me believe it's a tolerance.

https://www.digikey.com/product-detail/en/RSMF2FB392R/RSMF2FB392R-ND/1695205 which is non-stocked

:assuming its a 1.9kohm:

Brown - 1

white - 9

red - two 0's

1900 ohm or 1.9kohm

That resistor doesnt look nuked, if the heat that burned the board came from that resistor then its likely there would be signs of the resistor having been mad hot.
Might have a been a dry soldered joint on the board where the resistor connects, if the resistor measures a similar value then its probably ok.

Micro's run a several thousnad volts be carefull you dont get nuked, the cap holds volts for quite a while.

I revisited this thread to put this old info in a file on my computer. The 2009 repair is still good! Yesterday, I noticed an electronic/plastic burning smell inside the microwave. It worked and sounded normally while heating my coffee but I knew something was about to fail so I took it apart looking for burned wires. I found none. I checked the magnetron and capacitor and they were good but found the High Voltage diode open so ordered a new one for $15. Hopefully that's all that's wrong.

Generally, you'll need a 9V battery and resistor to check the HV diode. Set the current to 1-10 mA and measure Vd.

So, the hot water test for the magnetron. i.e. measure wattage it took to heat a specific qty of water

KeepItSimpleStupid said:

Generally, you'll need a 9V battery and resistor to check the HV diode. Set the current to 1-10 mA and measure Vd.

Click to expand...

Probably more than 9V, however the HV diodes NEVER go O/C, if they go faulty it's always S/C. And as he says the oven still works, then the diode certaibly isn't faulty.

However, it's interesting he claims to have checked the 'magnetron', I somehow suspect he hasn't - it's not something you can 'check', other than sticking it in an oven and seeing if it works.

Thank you for your replies. I found procedures for checking the magnetron and diode with a meter online. http://www.microtechfactoryservice.com/mag_test.html and http://www.microtechfactoryservice.com/diode.html I used a UEI DM383 meter to do the testing http://www.instrumentation2000.com/pdf/uei-dm383b-manual.pdf Both the diode function and the ohm function indicated an open diode. Could I have gotten a false reading? As stated earlier, the oven worked normally. I used my nose and eyes to locate the source of the odor. The smell was definitely emanating from the oven compartment. I'll install the diode and do some testing and post results. Thanks again!

On page 4 in the meter instructions it tells you the Diode test is no good on microwave oven diodes. They will test as open circuit.

Datasheet for a typical microwave diode: https://www.weisd.com/store2/NTE517.pdf

Vf = 14V; so you need two 9V batteries in series and a current < 550 mA, 10 mA would work.
R <= (2*9-14)/10e-3

Here http://www.microtechfactoryservice.com/output.html is the magnetron test.

The ohmmeter tests work for "no heat". they don;t work well for poor performance.

surfref32 said:

Thank you for your replies. I found procedures for checking the magnetron and diode with a meter online. http://www.microtechfactoryservice.com/mag_test.html and http://www.microtechfactoryservice.com/diode.html I used a UEI DM383 meter to do the testing http://www.instrumentation2000.com/pdf/uei-dm383b-manual.pdf Both the diode function and the ohm function indicated an open diode. Could I have gotten a false reading? As stated earlier, the oven worked normally. I used my nose and eyes to locate the source of the odor. The smell was definitely emanating from the oven compartment. I'll install the diode and do some testing and post results. Thanks again!

Click to expand...

Neither of those supposed 'tests' are of any use whatsoever, but as the oven is working both magnetron and diode (and all other functional parts) are working anyway.

Most likely cause of a smell would be burnt food inside, or a burnt waveguide cover (caused by not cleaning it).

Well folks, it looks like this was a false alarm. I read somewhere that the magnetron smells like burning plastic when its way out so I thought it was that. Then after finding those bogus test procedures, I thought it was the diode. It would have been smart of me to read all of that manual for my meter! As usual, experience plays a big role in these situations and my microwave repair experience is almost nil. I cleaned the waveguide covers but noticed the glass plate smelled like the burnt plastic I was looking for. I'm guessing one of my kids overheated something plastic in there and wouldn't admit to it. Lesson learned ; clean the inside of the microwave before assuming a part is burning. A big thank you goes out to Nigel, KISS and debe!

I've repaired hundreds (if not thousands) of microwave ovens.