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I own a KitchenAid built-in microwave unit, KEMS308GSS2. A while ago it stopped heating anything (no odd noises, full power). Ran a bunch of tests; fuse, magnetron, diode, etc. As best I could tell the diode was bad so I replaced it. The microwave worked for about a week, and then started working intermittently, now it does not heat at all again. When a magnetron goes, does it go completely or can it work sporadically as described above? Any other thoughts such as a bad capacitor or heat switch? Have meter and smart enough to be careful with high voltages….
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Rank: Advanced Member
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Disconnect the HV transformer from the source from the circuit board. Select a cook cycle and test to see if the board is putting out 120VAC to the transformer. This will tell you whether the problem is on the low, or the high voltage side. Let us know what you find.
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So of-course I once had the repair pamphlet that included the schematic, but do you think I can now put my hands on it? There are 8 wires that go from the transformer to a single connector on the circuit board, 2 yellows, 2 browns, 2 purples, and a blk and a white wire. Am I correct in assuming the blk and wht wires are my 120 volt wires? I’ll keep searching for the schematic (assuming my wife didn’t “accidentally” throw it out). I’ve been searching the web for this repair guide, but I can only seem to find the User Manuals and Parts List. Thanks!
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Rank: Advanced Member
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The black and white wires should be the power wires going to the transformer. If you disconnect them from the transformer, select a cook cycle. Meter the wire connections to them and see if you"rre gertting 120VAC. If you are, this indicates that the problem is in one of the high voltage components. If you don't get the voltage, or if it's too low, the problem is in the board.
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When I disconnect the connector at the pcb coming from the transformer to the board, I loose all power to the panel. I can not run any cycles once that happens. I tried to attach a pic of the connector on the pcb and the transformer it goes to, but I can’t seem to upload any pictures successfully. The pcb is one of two mounted back-to-back on the back of the control panel, and the connector is on the far right end of this board. The transformer is the large front-most transformer mounted to the upper right side of the oven cabinet. Am I barking up the wrong tree (connector)?
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Rank: Advanced Member
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Joined: 8/16/2007(UTC)
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You should be able to disconnect the wires that attach to the transformer itself, to run the test. Try going to this Web site and looking for a specific tech manual for your unit. You need to register; but registration is free. http://appliancejunk.com/forums/index.php
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Rank: Member
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Thanks for the pointer to the service manual site, they had what I was looking for and it has been a help, but….I’m still trying to figure this out. Here is what I have done so far:
1 – Disconnected the Primary Terminals from the HV Transformer.
2 – Ran a cook cycle measuring the input voltage to HV Trans = steady 120.
So LV side seems to be fine. Ran the following tests on HV comps:
Magnetron:
1 – Removed all wires to the terminals.
2 – Measured resistance (R x 1) from one term to the other = 0 ohms.
3 – Reversed leads from above, still 0 ohms.
4 – Measured resistance (R x 1K) from each terminal to housing = infinity.
5 – Visually inspected the unit and it looks fine.
Capacitor:
1 – Measured resistance (R x 1K) between the two terminals:
Initial reading = infinity
Swapped leads = High level resistance, then faded to infinity
Swapped leads again = High level resistance, then faded to infinity
2 – Measured both leads to metal case = infinity for both.
Diode:
My meter runs on 1.5 volts, and does not go beyond 1K ohms, so I don’t feel as though I can test this appropriately. But this is the part I just replaced recently, so unless the odds are against me I believe this part should be good.
HV Transformer:
1 – Disconnected all wires.
2 – Measured resistance (R x 1) between the two Primary Terminals = < 1 ohm.
3 – Measured resistance between the two orange leads = 0 ohms.
4 – Measured resistance between each terminal and chassis = infinity.
5 – Measured resistance from yellow secondary to chassis = about 80 ohms.
The service manual for this model says that the above test (#5 HV Transformer) should have equaled 0 ohms. But another diagnostic article suggests that it should read between 55 and 70 ohms.
In either case I’m leaning toward a bad transformer. Your thoughts or other suggestions?
Thanks again for all your help!
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Rank: Advanced Member
Groups: Senior Expert
Joined: 8/16/2007(UTC)
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You should have SOME resistance between the filament terminals on the magnetron. If there's no resistance at all, it could mean the connection between them is shorted.
Try this: run a test clip or wire from one terminal to the chassis. Test for a reading between the other terminal to the chassis. What do you get? Better yet, do the same test, using a resistor of a known value and see if your reading is any different from that of the resistor by itself.
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Rank: Member
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I get about 3 ohms with the first test. I will have to dig up a resistor to try the second test.
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Rank: Advanced Member
Groups: Senior Expert
Joined: 8/16/2007(UTC)
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In that case I agree with you about the transformer.
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