FIXED MC17J8000CG Samsung Microwave - No Heat

[c2z4s9]

Model Number

MC17J8000CG

Brand

Samsung

Age

1-5 years

Hello all, I have a MC17J8000CG Microwave unit that does not heat. I have tested the following:

All 3 door switches appear to work properly
All of the temperature safety switches appear to be okay (all low impedance)
The capacitor appears okay, as it appears as open circuit
Magnetron appears okay; The terminals measure low impedance between them, but are both open to the chassis.
Diode appears to work okay, current only flows one way
The HV Transformer primary measures less than 1 ohm, but the secondary measures 138 to 139 ohms.

This is where the problem lies. The literature statues the transformer secondary should measure 131 +- 2% which means a max of 133.62 ohms. This means, technically, a measurement of 138 to 139 ohms is out of spec, ,but just barely. Should I replace the transformer or continue looking for other problems within the unit?
Thanks!

 

[Jake]

Hi, I'm not that familiar with microwaves, but Rick mentioned this:

ME21H9900AS Microwave Transformer Bad?

Everything works on my microwave expect it does not heat anymore. Just stopped working one day. Turn table turns, lights come on, controls are fine. Just wont heat food no matter how long it runs for. I have tested the capacitor, diode, switches and temp sensors. All good. I have 120 volts...

www.applianceblog.com

Your model uses that same exact transformer.

Jake

 

[c2z4s9]

Okay. I did some more investigating.

I took my oscope and connected a high voltage probe up to the secondary output of the high voltage transformer and got this

60 Hz "high voltage". I wouldn't put too much stock in the measured voltage being too accurate. 7.5 kV sounds a bit too high to me.
I then checked the output side of the capacitor or the input to the magnetron and got this.

It is my understanding that beyond producing microwaves, the magnetron essentially operates like a diode. The microwave's high voltage transformer, capacitor, and diode work together to double the output voltage of the transformer (the waveform is negative going) when measured on the output side of the capacitor. When measuring the magnetron filament we see that the voltage stays at 0 until the voltage reaches some threshold and then is essentially held at that negative threshold and does not go further negative. But this result looks weird to me. First of all, the voltage is much lower than expected, and it looks like at some point while the magnetron is radiating that the voltage falls back towards 0 for (approximately) half the time is should be on. The magnetron should be working when the voltage is negative. I therefore started to suspect the magnetron.
I then removed the magnetron from the circuit by unplugging the connector to the filament and measured the output of the voltage doubler and measured this result.

So other than the absolute magnitude of the waveform this looks correct to me. The top of the waveform is 0 V and the bottom is some rather large (kV) voltage.

I then removed the magnetron and it appeared physically damaged.



To be clear when measuring the magnetron with a meter it measured okay, meaning that the impedance between filament terminals is very low (less than 1 ohm, I believe) and I was unable to measure any continuity between the filament and the body of the magnetron. However, it obviously appears damaged.
I replaced the magnetron and measured this when looking at the filament.

This looks correct to me. A couple thousand volts (but probably not accurately measured) and then no strange artifacts while the magnetron is radiating. Oh and I was able to heat up some water.
So it does indeed appear to have been the magnetron.

Hopefully this will help someone in the future.

 

[Jake]

Thanks for the added information you posted, that will help others too.

Glad the new magnetron fixed it!

Here's the magnetron for your model, in case others need it too: https://www.repairclinic.com/PartDetail/Magnetron/OM75P-10-ESHL/2095563

Jake