Connect with us

Faulty Microwave Oven

Discussion in 'Electronic Repair' started by Eric Bradley, Sep 25, 2004.

Scroll to continue with content
  1. Eric Bradley

    Eric Bradley Guest

    A few days ago we had a shock when our Samsung microwave oven switched
    itself on without anyone being near it.
    There were only my wife and myself in the house and we were nowhere
    near the kitchen, when we both heard the `beeping` sounds of the
    buttons being pressed,followed by the sound of the oven running. we
    both went into the kitchen to find that it had programmed itself to
    run for about 2 minutes, as the count down timer was on 1 minute 45
    seconds. We watched in amazement while the timer counted down to zero
    and the oven stopped.
    How could this happen, and can the `beeps` of the buttons being
    pressed be caused by a fault, or do the buttons have to be pressed to
    make the beeps.
    It made the usual 4 or 5 beeps as when we use it normally,except that
    there was no-one in the vicinity,
    Needless to say, we have unplugged the thing,untill we find the cause.
     
  2. John Miller

    John Miller Guest

    You didn't mention whether anyone else was in the house, or could have
    been (e.g., prankish intruder).
    Occam would suggest that human involvement, however unlikely, is less
    unlikely than spontaneous sequential button pushing.

    --
    John Miller
    email address: domain, n4vu.com; username, jsm
    Surplus (FSoT):
    New Conn V1 double trumpet case, no logo
    Tektronix 465B oscilloscope
     
  3. Eric

    Eric Guest

    Sorry I can not help you with your two minute problem,

    But NEVER run the microwave without something in it, you will burn out the
    magnetron



    A few days ago we had a shock when our Samsung microwave oven switched
    itself on without anyone being near it.
    There were only my wife and myself in the house and we were nowhere
    near the kitchen, when we both heard the `beeping` sounds of the
    buttons being pressed,followed by the sound of the oven running. we
    both went into the kitchen to find that it had programmed itself to
    run for about 2 minutes, as the count down timer was on 1 minute 45
    seconds. We watched in amazement while the timer counted down to zero
    and the oven stopped.
    How could this happen, and can the `beeps` of the buttons being
    pressed be caused by a fault, or do the buttons have to be pressed to
    make the beeps.
    It made the usual 4 or 5 beeps as when we use it normally,except that
    there was no-one in the vicinity,
    Needless to say, we have unplugged the thing,untill we find the cause.
     
  4. James Sweet

    James Sweet Guest


    There may be some truth to this myth, but I've run microwaves without
    anything in them a number of times as well as trying various metallic
    objects in a discarded oven, never did have one damaged from it.
     
  5. Eric

    Eric Guest

    That's what I was thinking John,

    But only Eric knows how true this could be,
    In which case, I wonder if the keypad could of gone faulty, this is why I
    like to unplug the primary side of the magnetron transformer when ever I
    work on microwaves, they give me the shits, until I am about to screw the
    cover back on.



    You didn't mention whether anyone else was in the house, or could have
    been (e.g., prankish intruder).
    Occam would suggest that human involvement, however unlikely, is less
    unlikely than spontaneous sequential button pushing.

    --
    John Miller
    email address: domain, n4vu.com; username, jsm
    Surplus (FSoT):
    New Conn V1 double trumpet case, no logo
    Tektronix 465B oscilloscope
     
  6. Hi!
    Maybe nobody cares...but here are two true stories of "abused" microwaves...

    I believed this until one night my little brothers got into an old Kenmore
    microwave that I was cleaning up. They basically punched all nines on the
    keypad and set it to go. It had been running empty for a little over 30
    minutes when I found it. The fan and magnetron had stopped, but the light
    was on inside. The smell around it suggested that something had cooked
    bigtime, but after letting it cool down everything was fine once again. It's
    still working to this day and will have 20 years on it come 2005.

    My grandmother bought a Litton microwave some awful number of years ago
    (really old machine...has a rotary timer on it!) and one of the first things
    she did (before reading the directions) was to put a large metal cooking pot
    inside. She started the oven and BANG...I've been told that it blew the
    glass out of the door. She had it fixed, and to this day it is also still
    running like new. I'd guess that it is at least 30 years old now...

    William
     
  7. But it DID blow the glass out of the dooe. :)

    --- sam | Sci.Electronics.Repair FAQ Mirror: http://repairfaq.ece.drexel.edu/
    Repair | Main Table of Contents: http://repairfaq.ece.drexel.edu/REPAIR/
    +Lasers | Sam's Laser FAQ: http://repairfaq.ece.drexel.edu/sam/lasersam.htm
    | Mirror Sites: http://repairfaq.ece.drexel.edu/REPAIR/F_mirror.html

    Note: These links are hopefully temporary until we can sort out the excessive
    traffic on Repairfaq.org.

    Important: Anything sent to the email address in the message header is ignored.
    To contact me, please use the feedback form on the S.E.R FAQ Web sites.
     
  8. Andy Cuffe

    Andy Cuffe Guest

    Running a microwave empty is bad for it because there's nothing to
    absorb the 700 Watts of microwave power coming out of the magnetron,
    so it all ends up going back into the magnetron. Eventually it will
    heat up enough to either trip the thermal breaker, or destroy the
    magnetron. Nothing will explode though.

    The dangers of putting metal objects in the microwave is more of a
    myth. It's true that certain things like crumpled foil will cause
    arcing, but this isn't dangerous and shouldn't hurt the oven. Things
    like metal twist ties can heat up and catch on fire. Keep in mind
    that the oven walls are made of metal and metal temperature probes
    have been around for years. You're generally ok with flat metal
    objects, or even things like spoons and wire racks. You don't want to
    use metal pots because they will shield the thing you're trying to
    cook from the RF.
    Andy Cuffe
     
  9. James Sweet

    James Sweet Guest


    Did someone happen to clean the control panel with spray cleaner? Depending
    on the design, some moisture may have run down into the keypad and caused
    random button presses.
     
  10. Eric

    Eric Guest

    I heard of someone how used to wreck microwaves, he thought he had to "pre
    heat" them for a few minutes.





    There may be some truth to this myth, but I've run microwaves without
    anything in them a number of times as well as trying various metallic
    objects in a discarded oven, never did have one damaged from it.
     
  11. Guest

    We use the microwave at work to destroy recordable CDs. About 5
    seconds give a nice light show as the subtrate build up a charge and
    starts arcing internally. It very nicely destroys the disk and
    usually the layers will separate.
     
  12. James Sweet

    James Sweet Guest


    Well if you run them for a few *minutes* with nothing in them as someone
    else said, it can overheat the magnetron, but a few, or even tens of seconds
    generally won't cause any problems.
     
  13. Eric

    Eric Guest

    what's wrong with people at this group?


    The person who started this topic said the microwave ran for two minutes.
    that's when I added my warning.








    Well if you run them for a few *minutes* with nothing in them as someone
    else said, it can overheat the magnetron, but a few, or even tens of seconds
    generally won't cause any problems.
     
  14. Chuck Harris

    Chuck Harris Guest

    Nope! There is nothing inside the magnetron that can absorb power. All that
    happens to any microwaves that head back towards the magnetron cavity
    is they reflect back into the oven. Unless something that absorbs microwaves
    is put into the cavity, the 700W is never created. The oven is a resonant
    cavity with very high Q. What does happen when the cavity is left unloaded,
    is very high voltage nodes are setup in the cavity space. Depending on
    where they happen to be, some arcing might occur. The oven's designers
    were very careful to make sure that that doesn't happen. Modern ovens
    are designed to withstand being run empty indefinitely.

    When you put metal objects into a microwave oven, again, you run the risk
    of causing localized areas of high voltage, that may cause arcing. You
    also will get localized areas of high current on the metal object which
    may cause parts of it to get extremely hot.

    -Chuck
     
  15. [This followup was posted to sci.electronics.repair and a copy was sent
    to the cited author.]

    Does it have a delay start mode, where you can tell it to start
    running at a certain time? Maybe somebody accidently set that mode by
    hitting the wrong keys, and it later finished that program?
     
  16. Hi!
    To be honest with you, I don't know if that's impossible or not...the whole
    thing happened a good while before I was even alive and I'm sure it's one of
    those stories that gets a little better each time it's told.

    All I can say for sure is that the microwave was somehow seriously damaged
    and it was repaired...and that it still runs today without any lasting
    effect.

    William
     
  17. So, it's possible the magnetron was replaced?

    --- sam | Sci.Electronics.Repair FAQ Mirror: http://repairfaq.ece.drexel.edu/
    Repair | Main Table of Contents: http://repairfaq.ece.drexel.edu/REPAIR/
    +Lasers | Sam's Laser FAQ: http://repairfaq.ece.drexel.edu/sam/lasersam.htm
    | Mirror Sites: http://repairfaq.ece.drexel.edu/REPAIR/F_mirror.html

    Note: These links are hopefully temporary until we can sort out the excessive
    traffic on Repairfaq.org.

    Important: Anything sent to the email address in the message header is ignored.
    To contact me, please use the feedback form on the S.E.R FAQ Web sites.
     
  18. James Sweet

    James Sweet Guest

    He never said it failed either, he unplugged it and hasn't used it since.
     
  19. b

    b Guest

    (snip)

    I would dismantle and thoroughly clean the control panel with alcohol
    - if possible. If it is damaged (e.g. buttons are in permanent
    contact, and /or can't be dismantled further for re-gapping of
    contacts) you may have to salvage a panel from a junk unit of the same
    model as ordering a new part would probably exceed the cost of a new
    oven (that is if the spares are even available). *Read the FAQ for
    important safety guidelines as these units can kill.*

    Ben
     
  20. Eric

    Eric Guest

    I know, I know they have unplugged it, but they were watching it for a
    couple of minutes, while it counted down, I take it there was nothing in the
    microwave, that is why I gave the warning.




    He never said it failed either, he unplugged it and hasn't used it since.
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-