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Where to look for microwave oven fault?

Discussion in 'Electronic Repair' started by Eric R Snow, May 8, 2004.

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  1. Eric R Snow

    Eric R Snow Guest

    Greetings All,
    My microwave oven just quit heating. Before I scrap it for parts maybe
    I can instead fix it. When set to defrost the power cycles on and off.
    And you can tell by the lower fan sound and the light slightly dimming
    when it is supposed to be heating.. It still does this but nothing
    gets hot. Whether defrost or full power. So, I think the transformer
    must still be getting power. Any thoughts? Do magnetrons eventually
    fail? I have another oven that's over twenty years old and it still
    works fine.
    Thank You,
    Eric R Snow
     
  2. Art

    Art Guest

    Suggestion, if you don't know the safety procedures to troubleshoot these
    devices take it to a service center. They can be lethal when improperly
    serviced. Numerous things may cause the unit to not heat. Inclusive of
    controller defect, thermal cut-out devices, safety switches failing or
    mis-adjusted, defect in the HV diode - Capacitor area, Magnetron, and
    Transformer. Of course, interconnects, etc can also cause problems. Again,
    unless you know how to work on these items, for your own safety, do not!!
     
  3. I double what Art said.

    No offense intended, but microwave ovens are definitely NOT for
    inexperienced troubleshooters. The high voltages inside can really put you
    in a world of hurt.

    Besides, microwave ovens are so inexpensive now that you can probably buy
    one new at Y'all Mart cheaper than a replacement magnetron would cost.
     
  4. Eric R Snow

    Eric R Snow Guest

    It bugs me to throw away something when it can be fixed. And I don't
    shop at wall mart. I won't be trying to trouble shoot this thing
    powered up. If it can't be done that way then I'll get a new one. I
    know about high voltage and know enough not to mess with it. Can the
    HV diode be checked with a VOM?
    ERS
     
  5. Ricky Eck

    Ricky Eck Guest

    I will have to agree with the two previous post. Trouble shooting a
    Microwave is quite a task sometimes. I used to work with them about 10
    years ago, and they were complex even then. Now with the technology we have
    today, I wouldn't even open one up. Plus I don't have the equipment to do
    it anymore. Unless someone has a special trick, you will need more then
    just an OHMS meter to trace a problem.

    My suggestion. If you are not experienced with Microwaves, don't do it.
    You could attempt it, but the money you will spend, will out the cost of a
    new one. If you took it to a shop, you might get lucky and they get by with
    using a used part, and find the problem right off the bat, the cost would be
    low.

    But if you insist on getting suggestions, my first thought was the
    Magnetron, however, after reading Art's post, I have to agree with him.
    There are several areas to check. There is something that is preventing the
    Magnetron from working. You will have to track it down. But then again, I
    am still working with knowledge I used 10 years ago. Technology has made
    quite a bit advancements since then.

    Once again, as the other's suggested, dispose of the unit, and get a new
    one. If you insist on repairing it, take it to a shop that has all the
    equipment and knowledge to work with them. If you decide that you want to
    try it yourself, please be careful. I worked on a TV the other day that I
    know I discharged the Flyback, and I still got a good jolt from it (nothing
    life threatening, but enough to let me know I was careless upon discharging
    it). Just be careful! (Ok, enough for me, I will step down from my soap box
    now..:)

    Rick
     
  6. Guest


    That was part of the warning. A microwave, particulary a
    malfunctioning one, can hold lethal voltage even after being
    unplugged. Don't even think about sticking a cheap VOM on anything
    while it's plugged in.

    -Chris
     
  7. mike

    mike Guest

    You've been given a lot of GOOD advice NOT to work on it if you don't
    know what you're doin'. You can kill yourself even if it's been off
    for a long time.

    I'd vote for a bad diode or cap. Mine has fuses that blow when the
    diode shorts. No, you need to put some volts on the diode to test it.
    Typical meter on ohms doesn't put out enough volts to turn it on.
    Of course, if it's shorted, you can see that.

    Remember, the cap can kill you!!!!! If you think you can check the
    cap for volts with your meter, think again. Cheap meters will blow up
    on a fully charged cap. You'll hurt yourself on the sharp metal when
    you come flying out of the case. Make sure you pee before you start.
    Smaller wet spot to clean up...assuming you live.
    mike

    --
    Return address is VALID.
    Bunch of stuff For Sale and Wanted at the link below.
    Toshiba & Compaq LiIon Batteries, Test Equipment
    Yaesu FTV901R Transverter, 30pS pulser
    Tektronix Concept Books, spot welding head...
    http://www.geocities.com/SiliconValley/Monitor/4710/
     
  8. Eric R Snow

    Eric R Snow Guest

    I should have said I know about how to discharge a cap. I know that
    dangerous voltages (lethal) can be stored a long time. I won't be
    sticking a crappy VOM or my fingers or anything else conductive where
    it shouldn't be. I won't be doing anything with the power on. I won't
    be pointing the magnetron at my crotch. What I would like to know is
    if there is something I can check after the HV xmfr with a VOM. If
    not, then it gets trashed. (I do need another xmfr for that spot
    welder). Thanks for the warnings.
    Cheers,
    Eric
     
  9. See the Microwave Oven Repair Guide at the site below.

    However, the warnings of the others should be taken most seriously.
    The microwave oven is by far the most lethal of all consumer electronics
    and appliances. The magnetron is powered by a circuit that can provide
    up to 5 thousand volts at a substantial fraction of an AMP or more.
    One doesn't get a second chance.

    Even when unplugged, there is a high voltage capacitor that can retain
    a nasty charge.

    At least read the SAFETY info.

    --- sam | Sci.Electronics.Repair FAQ Home Page: http://www.repairfaq.org/
    Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
    +Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
    | Mirror Site Info: http://www.repairfaq.org/REPAIR/F_mirror.html

    Important: The email address in this message header may no longer work. To
    contact me, please use the feedback form on the S.E.R FAQ Web sites.
     
  10. Not necessarily. While I agree with you on the warnings of the previous
    posts, it is possible to troubleshoot most microwave oven faults with
    little more than an ohmmeter and common sense. In fact, one of the things
    to be avoided is testing it live.

    In this case, the problem could be as simple as a bad connection to the
    magnetron filament wiring.

    However, it is essential to read and understand the SAFETY implications
    of working on a microwave oven.

    --- sam | Sci.Electronics.Repair FAQ Home Page: http://www.repairfaq.org/
    Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
    +Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
    | Mirror Site Info: http://www.repairfaq.org/REPAIR/F_mirror.html

    Important: The email address in this message header may no longer work. To
    contact me, please use the feedback form on the S.E.R FAQ Web sites.
     
  11. hemyd

    hemyd Guest

    My own experience as an amateur to repairing microwave ovens might be
    worthwhile to describe -
    Being fully aware of the extreme danger in working on one of these things, I
    was very careful when my unit stopped heating. I checked out the various
    interlock switches; I checked (VERY carefully) the operation of the
    transformer; the diode SEEMED ok when doing a resistance check with a
    multimeter, however I did not want to part with the money for a new one, so
    I looked into it further. I referred to the trusty www.repairfaq.org and,
    sure enough, found the manner in which I could test this properly. I found
    the diode was ok. That left only the magnetron. At that point I decided it
    was much cheaper (and safer) to buy a new microwave oven at a discount
    store.

    Henry,
    Australia
     
  12. Steve Kraus

    Steve Kraus Guest

    It sounds like that is the best plan. Safely discharge the cap, do what
    tests are possible with the diode but otherwise just give it a general
    looking over in case it really is just a bad connection somewhere...but if
    nothing looks out of the ordinary then scrap the unit. Keep in mind that
    this is the most likely outcome.
     
  13. Z

    Z Guest

    Quite right- to do so is wasteful! It's a moral duty to get it fixed
    and not to use up more land-fill.

    Go on open it up dead, a lot of faults with microwave ovens are caused
    with vapours entering the electrical compartments.
    What's a VOM?
     
  14. James Sweet

    James Sweet Guest

    Huh? Dangerous if you don't know what you're doing yes, but complex? Hardly,
    they're about the simplest appliance there is, really not much to them, a
    magnetron, transformer, capacitor, diode, some interlock switches and a
    control board, that's about all that's in there. Only thing I've ever seen
    fail on the control board has been solder joints and occasionally the triac.
    Most common problem is a blown fuse, microwaves are the only thing I've seen
    regularly blow a fuse with no apparent problems otherwise. Next most common
    problem is a bad interlock switch. Transformer almost never fails,
    magnetron, diode and cap are all pretty easy to test, however I NEVER do
    live testing on these, always unplug it and discharge the capacitor. I leave
    a jumper clip across the cap until I'm done working in there, just don't
    forget to remove it.
     
  15. Ricky Eck

    Ricky Eck Guest


    Volts Ohms Meter
     
  16. Translation: One with a meter needle instead of an LCD. :)

    --- sam | Sci.Electronics.Repair FAQ Home Page: http://www.repairfaq.org/
    Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
    +Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
    | Mirror Site Info: http://www.repairfaq.org/REPAIR/F_mirror.html

    Important: The email address in this message header may no longer work. To
    contact me, please use the feedback form on the S.E.R FAQ Web sites.
     
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