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Sharp Microwave powers down after 40 seconds, need assistance

Discussion in 'Electronic Repair' started by electroninja, Jan 7, 2005.

  1. Pointing more to the controller.

    --- 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 above is
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  2. Figured after all the tests he had done he would know enough not to test without
    cap.discharged as he had read your article.Anyway I did say to switch on whilst
    testing fil.voltage when connected and not connected.
    I agree with the danger,this is the first road I would go down coupled with
    mag.filament/case continuity test.Last repair on Sharp I did close to this was
    the thermal cut out but he said he'd discounted this.
    Maybe worth another look ranges are 127C to 88C approx for open and reset.



    "Texas Hold'em Poker"

    "The bigger you bet,the less you win when you lose!"
     
  3. electroninja

    electroninja Guest

    Sam--the contoller board has a hardwired LC6041 chip. My spare parts
    microwave has the same chip and it works. Ever tried to unsolder a 48
    pin LC without damaging it thru overheating?

    Harry--this unit has only one thermal cutoff switch physically mounted
    on the casing surrounding the magnetron--electrically it is upstream of
    all loads and were it to activate it would shutdown everything (lights,
    fans, control display.. etc)--which is not the case here. Thoughts?
    Thanks for all comments--
     
  4. electroninja

    electroninja Guest

    Update:

    --Removed the panel unit (selector buttons, control and relay boards)

    --Visual inspection shows a zener diode (panel marking Z02) that has
    overheating signs (black outline around diode.) The zener is 3/16 long,
    with a diameter of a round toothpick and is much larger than other
    zeners on the board.

    Question: Does anyone know a way to determine proper zener replacement
    visually?(markings, color codes etc.) Plan to replace this diode.

    Recommendations: Manufacturer no help to this point--authorized
    factory rep in local area has no listing for the Sharp R1810.
    Thanks!
     
  5. NSM

    NSM Guest

    | Update:
    |
    | --Removed the panel unit (selector buttons, control and relay boards)
    |
    | --Visual inspection shows a zener diode (panel marking Z02) that has
    | overheating signs (black outline around diode.) The zener is 3/16 long,
    | with a diameter of a round toothpick and is much larger than other
    | zeners on the board.
    |
    | Question: Does anyone know a way to determine proper zener replacement
    | visually?(markings, color codes etc.) Plan to replace this diode.

    WITH GREAT CAUTION (Avoid Death) measure the voltage present on the diode
    and select a lower voltage.

    N
     
  6. electroninja

    electroninja Guest

    NSM:

    Not exactly sure what you mean by "select a lower voltage." According
    to:
    www.americianmicrosemi.com/tutorials/zener.htm

    the "zener diode voltage must be specified" for circuit operation. They
    go on to say "...the breakdown voltage is the zener voltage for
    operation and is intended to operate at that voltage..." I like your
    idea to check the operational voltage at the diode connections (suspect
    diode heating breakdown at 40 sec however) but can you tell me what
    watt diode this might be given the size or other physical markings?
     
  7. electroninja

    electroninja Guest

  8. NSM

    NSM Guest

    | NSM:
    |
    | Not exactly sure what you mean by "select a lower voltage." According
    | to:
    | www.americianmicrosemi.com/tutorials/zener.htm
    |
    | the "zener diode voltage must be specified" for circuit operation. They
    | go on to say "...the breakdown voltage is the zener voltage for
    | operation and is intended to operate at that voltage..." I like your
    | idea to check the operational voltage at the diode connections (suspect
    | diode heating breakdown at 40 sec however) but can you tell me what
    | watt diode this might be given the size or other physical markings?

    If you find. say, 12.3 VDC across the terminals (assuming the old diode is
    open circuit) then I'd try 10 VDC. As for power I would eyeball it.

    Or, you could get a selection of diodes and slowly substitute them, going
    from the lowest voltage to the highest. It's a crap shoot situation. Of
    course, if you can trace the diode directly to a chip that needs 5 VDC then
    problem solved. But the diode may be the supply for the temp probe bridge
    circuit.

    N
     
  9. electroninja

    electroninja Guest

    NSM--

    Help me out here--you/ve mentioned the temp probe twice now and you've
    sent me in previous correspendence to
    http://www.euras.com/repair_tip_/sharp/R1810/R1810-sharp.htm, an
    overseas repair service.

    I don't want to offend anyone trying to help me, but I've got to ask
    you--Do you have a repair manual--and is it pointing to the temp probe
    bridge?
     
  10. NSM

    NSM Guest

    | NSM--
    |
    | Help me out here--you/ve mentioned the temp probe twice now and you've
    | sent me in previous correspendence to
    | http://www.euras.com/repair_tip_/sharp/R1810/R1810-sharp.htm, an
    | overseas repair service.
    |
    | I don't want to offend anyone trying to help me, but I've got to ask
    | you

    : Do you have a repair manual?

    No. Is there one?

    Apart from the aforementioned site which in fact has only this fault: "LIST
    OF FAULT SYMPTOMS: Operates for 2 minutes and shuts down. Cooling fan motor
    runs continuously or operates intermittently" which seems to be almost
    exactly your fault, it seems there is no service support. I'm giving you the
    best advice I can under the circumstances.

    FWIW, it's easy to become too hung up on the 'right way' as if it was god
    given. Example: If the zener diode is open, a new diode cannot make the
    problem worse so try it and see. That's what the pros do - believe it or
    not. Servicing isn't about some sort of magic finding of the right answer -
    it's about not wasting time on things which cannot be the problem - as
    Sherlock Holmes was wont to say, "When you have eliminated all which is
    impossible, then whatever remains, however improbable, must be the truth".

    N
     
  11. electroninja

    electroninja Guest

    NSM

    I appolize for offending you but I do apprieciate your input--in
    review:

    --System operates for 40 seconds then shutsdown (fan included but not
    monitor lights)

    --Only system fault detected thus far is an over heating zener diode on
    the control circuit board

    Not sure what FWIW means because I'm truly new to all of this--however
    I do appreciate your input and help. I will sub the zener--however I
    perfer "not to wastetime on time on things which cannot be the problem"
    as you suggest. I'm sure you can't be saying replacing the zener is a
    waste of time? Still waiting for some best guess on watt rating for
    replacement.

    Can't quote Holmes but I remind you of an old Sgt Friday phrase "just
    the facts mam."
     
  12. Huh (about the safety warning)? It's probably a 5 V or 12 V diode.

    Indeed, simply measure the voltage across the diode. The microwave
    doesn't need to be running as long as the control board is alive.

    What are the markings on it?

    --- 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 above is
    ignored unless my full name is included in the subject line. Or, you can
    contact me via the Feedback Form in the FAQs.
     
  13. Why?

    If I find 12.3 VDC across a zener, I expect it to be approximatley a
    12 V zener.

    --- 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 above is
    ignored unless my full name is included in the subject line. Or, you can
    contact me via the Feedback Form in the FAQs.
     
  14. electroninja

    electroninja Guest

    Repeat of Update:


    --Removed the panel unit (selector buttons, control and relay boards)


    --Visual inspection shows a zener diode (panel marking Z02) that has
    overheating signs (black outline around diode.) The zener is 3/16 long,
    with a diameter of a round toothpick and is much larger than other
    zeners on the board.


    Question: Does anyone know a way to determine proper zener replacement
    visually?(markings, color codes etc.) Plan to replace this diode.


    Recommendations: Manufacturer no help to this point--authorized
    factory rep in local area has no listing for the Sharp R1810.

    Thanks!
     
  15. If it's fatter, I'd suggest 1 W is probably the correct power rating.

    --- 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 above is
    ignored unless my full name is included in the subject line. Or, you can
    contact me via the Feedback Form in the FAQs.
     
  16. electroninja

    electroninja Guest

    Sam

    I don't see any markings on the diode yet--perhaps when its removed
    from the circuit--will advise at that point.

    Thank you for your recommendations--I've reviewed the list of your
    work--I must say that for a person of your stature to spend time
    helping people like me hunt down microwave problems is commendable--god
    bless.
     
  17. NSM

    NSM Guest

    | > If you find. say, 12.3 VDC across the terminals (assuming the old diode
    is
    | > open circuit) then I'd try 10 VDC. As for power I would eyeball it.
    |
    | Why?
    |
    | If I find 12.3 VDC across a zener, I expect it to be approximatley a
    | 12 V zener.

    I'm assuming the zener is open (OP says burned out). I'd also look for other
    clues to voltage - cap rating, chip rating etc. This would be easier to fix
    if he had another working unit!

    N
     
  18. NSM

    NSM Guest

    | Sam
    |
    | I don't see any markings on the diode yet--perhaps when its removed
    | from the circuit--will advise at that point.
    |
    | Thank you for your recommendations--I've reviewed the list of your
    | work--I must say that for a person of your stature to spend time
    | helping people like me hunt down microwave problems is commendable--god
    | bless.

    How tall are you Sam?

    N
     
  19. NSM

    NSM Guest

    | > WITH GREAT CAUTION (Avoid Death) measure the voltage present on the
    diode
    | > and select a lower voltage.
    |
    | Huh (about the safety warning)? It's probably a 5 V or 12 V diode.

    I'm not sure of the skill level of the OP. Digging into the 'guts' like this
    carries more hazard of accident IME unless you know how to remove the HV
    danger. Too easy to get distracted.

    N
     
  20. electroninja

    electroninja Guest

    Sam

    I'm ready to test the diode voltage--DC voltage setting correct?
     
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