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Over Range Microwave: Exhaust Fan and Heating Issues

Discussion in 'Troubleshooting and Repair' started by Emithez, Nov 21, 2019.

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  1. Emithez

    Emithez

    2
    0
    Nov 21, 2019
    Hello,

    A couple of weeks ago I heard my microwave making a noise, sounded like a fan was going up in RPMs and then down again. Might not have been a fan, could have been the magnetron. Anyhow, I went outside a few hours and came back in and my wife said the microwave made a "pop" noise and wouldn't turn on. The microwave was pretty hot as one can imagine.

    I'm pretty handy when it comes to pretty much anything in or around my house. I took the microwave apart and the only issue I found initially was a blown thermostat fuse (likely the pop she heard). I ordered a fuse and put it in and got power back to the microwave LCD screen.

    Once I had power back I noticed 2 issues:
    1. The microwave wouldn't heat.
    2. The exhaust fan (not the cooling fan) would not turn off. As long as the microwave has power, the exhaust fan turns on.

    My initial assumption was it's the circuit board because all of the buttons would work with the exception of the fan On/Off button. Ordered new board and issue is still present.

    I tested all of the thermostat type fuses (4 of them I think) for continuity and they are good. I tested all ceramic fuses (2 of them on a small circuit board separate of the main board) and the door switches (3 of them) and everything tests good. I also tested the HV cap, magnetron and HV transformer and all of those devices test within spec.

    So, what am I missing? Is it possible for a magnetron to test good and be bad or maybe the same for the HV cap. I don't think it's the transformer but at this point I am down to the big 3. And I'm not sure that any of those 3 would have an effect on the exhaust fan.

    Could the issue be the small circuit board (it does have a copper coil and a couple other small soldered components). I'm not sure what that board's function is entirely, but I assume it servers to deliver power to particular components since it has the 2 ceramic fuses on it.

    Any thoughts would be much appreciated.
     
  2. 73's de Edd

    73's de Edd

    2,922
    1,235
    Aug 21, 2015
    Brand and model #
     
  3. Tha fios agaibh

    Tha fios agaibh

    2,107
    708
    Aug 11, 2014
    My guess: Hv diode shorted and relay contacts melted together.
    If relay case is not melted, you might get lucky and unstick contacts with a forceful whack of a screwdriver.
     
  4. Emithez

    Emithez

    2
    0
    Nov 21, 2019
    Sorry, the model is: Samsung ME18H704SFG

    Also, I tested to diode and it tests correctly. I put about 18v on it and it tested around 14v if I recall correctly. I think my heating issue might be the relays for the HV Transformer. I'm not seeing 120v (or any voltage) coming to the wires that plug into the large winding side of the transformer. I am going to test the relays with a 9v battery and see if they click and then test continuity.

    However, the exhaust fan issue has me stumped. I guess it could be the relay for the On/Off for the exhaust fan but this is a new circuit board, I find it hard to believe that the new board has the exact same issues as the old board (if there are any issues at all).
     
  5. Tha fios agaibh

    Tha fios agaibh

    2,107
    708
    Aug 11, 2014
    Perhaps there's an external relay?

    Post some pictures of what you've got.
    I can't find any online wiring diagrams to reference.

    If magnetron isn't getting power I'd look at door interlock switches (again)
     
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