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Sharp Microwave powers down after 40 seconds, need assistance

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

  1. electroninja

    electroninja Guest

    Took another look at the diode numbers under bright lights--marking is
    2.0B1--the dot between the 2 on 0 is centered vertically like 2-0B1.
    Still reviewing circuit
     
  2. NSM

    NSM Guest

    | Sam,
    |
    | Just reviewed your paper on "Basic Testing of Semiconductor Devices..."
    | and as a result retested diode. Analog readings were 4.7K and 2.7K
    | ohms--still bad I assume.
    |
    | Will attempt to better trace circuit--also I've noticed Radio Shack has
    | really changed from the old days--where is Allied Radio when I need them

    Might as well look for a Lafayette Radio store as expect help from R/S.

    N
     
  3. electroninja

    electroninja Guest

    NSM--ahh my canadian friend you are so right. Also, your idea to start
    substituting low and going high is starting to sound pretty darn good
    about now!

    Sam--I've tried to trace the circuit as you requested. The zener is
    involved directly with only two 25V capacitors and one 35V. The 35V is
    right at the power supply ground. Starting at the black band--the zener
    is in series with a 25V 100uf cap paralleled with a 1/4 W resistor
    ending on pin 32 of 38870L25. Between the cap and pin 32 a transistors
    collector is attached with the base truncating on pin 5 of the L25.

    Back to the diode--moving towards the power supply is a 25V cap to
    ground. Between the diode and cap is a wire to pin 12 of L25. A 35V
    1000uf capacitor is grounded from the same voltage bias as the 25V cap
    ground point then it (35V cap) tuncates at the power supply

    I'm sure this isn't much help but the circuit looks like my wife's
    spagettii dinners.

    In review for people seeking to help: 1. Need the voltage and power
    rating for a 2-0B1 zener diode (DZ2) on a Sharp R1810 microwave control
    unit printed circuit board (H6C08) or 2. Good guess on voltage rating
    for a suitable zener substitution for 2-0B1.

    If anyone knows the working voltage for a 38870L25 that might help
    also.

    Thanks
     
  4. electroninja

    electroninja Guest

    Can anyone put their hands on a "GE Tansistor Manual" published
    mid-1980's to research the 2-0B1 (2-DB1?) I have a 1964 GE publicaton
    that does list BD series diodes--they are called back diodes? Could
    they be the old term for zener's?
    Thanks.
     
  5. Franc Zabkar

    Franc Zabkar Guest

    See the HZ2 zener diode at this URL:
    http://www.has.hitachi.com.sg/databook/Hitachi/Diodes/HZ.pdf

    The "B1" probably refers to the voltage tolerance, in this case 1.9 -
    2.1V.


    - Franc Zabkar
     
  6. Franc Zabkar

    Franc Zabkar Guest

    The S1VB is a bridge rectifier. Is it possible that the circuit looks
    like this:


    uP-32 0--------|
    | +||
    |---||----|
    | || C |
    | |
    |-----| | \ |
    o--|~ +|--- R --|--|<|----|
    AC |S1VB | \ ZD |
    o--|~ -|------------------|
    |-----|

    Is the 38870L25 device the uP for the LCD?


    - Franc Zabkar
     
  7. Franc Zabkar

    Franc Zabkar Guest

    Looks like a Sanyo uP. Can't find its datasheet, though. :-(
    http://service.semic.sanyo.co.jp/semi/search_ds_e.htm
    Many times. TV and VCR uPs are of this type. Just use a variable
    temperature iron and a solder sucker with strong suction, eg a
    Soldapullt. I re-tin all the pins before starting. Often you can
    desolder two pins in one go if you bridge them with solder beforehand.

    - Franc Zabkar
     
  8. electroninja

    electroninja Guest

    My plan was just to remove the old LC and solder in a chip base--then I
    wouldn't have to worry about overheating the new chip. I'm assuming the
    LC61401 is a standard chip with no company EPROM giz stuff internal to
    it.
     
  9. NSM

    NSM Guest

    | My plan was just to remove the old LC and solder in a chip base--then I
    | wouldn't have to worry about overheating the new chip. I'm assuming the
    | LC61401 is a standard chip with no company EPROM giz stuff internal to
    | it.


    Somewhere there is a ROM with the program. It's more likely to be in the
    LC61401 than elsewhere. Can you see any other chips?

    N
     
  10. electroninja

    electroninja Guest

    Yes, two chips: one 38870L25 located on a smaller board between the
    relay board and the control board chip 064 604101 (on largest board
    nearest the time display/function switches). I have a spare 6041 in a
    Sanyo microwave that works and assume the chip is the same even though
    it does have the last two digits (01). I guessing its like the old 6502
    chip in that reguard.
     
  11. electroninja

    electroninja Guest

    Yes, two chips: one 38870L25 located on a smaller board between the
    relay board and the control board chip 064 604101 (on largest board
    nearest the time display/function switches). I have a spare 6041 in a
    Sanyo microwave that works and assume the chip is the same even though
    it does have the last two digits (01). I guessing its like the old 6502
    chip in that reguard.
     
  12. electroninja

    electroninja Guest

    Frank I think we're getting closer on the diode mystery--the incircuit
    voltage was 2.3-2.4volts when operating. Your chart indicated HZ2B1
    limits are 1.9-2.1----diode marks appear to be 2-0B1 printed in black
    ink around the radius of the zener. I substituted the old zener with a
    5.1volt and the circuit did not like that at all--monitor lights dimmed
    to the point where one couldnt read them. Didn't damage
    anything--replaced old zener and ops went back as they were.
    Thanks for the help
     
  13. electroninja

    electroninja Guest

    Circuit board seems to have two varicaps or varistors on the largest
    power board (604101). Found one supply house that sells only one
    component for this board--a varistor. Seems odd. In 1986, when this
    unit was made, does anyone know what designers used for timing
    control--no 555 chips to be found. Any posibility of a tunnel diode
    oscillator circuit for timing or temp control. The zener diode in
    question appears (thanks Franc Zabkar) to be a 2 volt diode running in
    the circuit at 2.23-2.24 volts. If it were intended to bias a tunnel
    diode oscillator circuit, the extra .24 volts might mess everthing up.
    Any ideas?
     
  14. There may be a 32,768 Hz crystal for the clock or the micro divides
    down its clock. Forget tunnel diodes. :) Anyhow, if the countdown works,
    the clock is working. The fact that it cuts out in 40 seconds or so
    means the firmware or hardware is corrupted or being told to shut off.

    --- 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.
     
  15. NSM

    NSM Guest

    | Circuit board seems to have two varicaps or varistors on the largest
    | power board (604101). Found one supply house that sells only one
    | component for this board--a varistor. Seems odd.

    That may be because they have those in stock anyway.

    | In 1986, when this
    | unit was made, does anyone know what designers used for timing
    | control--no 555 chips to be found.

    The CPU does the timing.

    | Any posibility of a tunnel diode
    | oscillator circuit for timing or temp control.

    None at all.

    | The zener diode in
    | question appears (thanks Franc Zabkar) to be a 2 volt diode running in
    | the circuit at 2.23-2.24 volts. If it were intended to bias a tunnel
    | diode oscillator circuit, the extra .24 volts might mess everthing up.
    | Any ideas?

    I'm afraid at this point remote diagnosis seems unlikely to help further.

    N
     
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