1. Rest in Peace Paul (Kegger) If you would like to help the family in this time of great sorrow and need, you may donate on their GoFundme page: https://www.gofundme.com/mckechnie-medical-and-funeral-fund?
    Dismiss Notice

Troubleshooting a Dehumidifier

Discussion in 'General Off Topic Forums' started by toxcrusadr, Jun 3, 2017.

  1. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    22,434
    Location:
    uk.. the middle bit
    is tr3 getting its base voltage to turn on ?
    looks to be 3rd pin up on cn14
    3rd pin down looks like always 12v supply
     
  2. toxcrusadr

    toxcrusadr AK Subscriber Subscriber

    Messages:
    27,455
    Location:
    Central Missouri
    [crossposted, let me look at your question]

    I will give you a tour.

    Power xmfr at left center, rectifier bottom left.
    To the right of that you'll see three filter caps C 2, C3, C5.
    Also two 3-pin devices IC1 and IC2 which are the 5V and 12V regulators. IC2 is the 12V and its output is at the top. IC1 is the 5V and its output is at left.
    Just above those are the 3 control transistors TR1, 2, and 3.
    The yellow and orange wires are the ones I soldered onto the compressor relay. The compressor ran when I applied +12V to the orange wire so that's marked +.
    Above that at the top of the board are the lugs for connecting the compressor and fan.
    To the left of the compressor relay are two smaller relays for the fan speeds.
    There seems to be a trace going to the left of my + mark through those fan relays, turning down at D6, going through J1 (jumper) to the output of IC2. This is what I found puzzling.
    Finally CN14 on the right edge of the board is the connector that goes to the brain board. Note, the third terminal from the top of that row connects to the compressor relay. BUT that pin is not used on the connector so it is not connected to the brain board.
     
  3. toxcrusadr

    toxcrusadr AK Subscriber Subscriber

    Messages:
    27,455
    Location:
    Central Missouri
    Ah so now you already have the answer: third pin from the top on CN14 is not used!

    Wait let me check the third pin from the bottom.
     
  4. toxcrusadr

    toxcrusadr AK Subscriber Subscriber

    Messages:
    27,455
    Location:
    Central Missouri
    Third pin from the bottom on CN14, referenced to the top pin which seems to be a big common bus that goes back to the rectifier, has no voltage when the machine is powered up and the fan is running. NOt sure where else I should measure it against. Also tried the '-' terminal (my yellow wire) and no voltage to there either.
     
  5. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    22,434
    Location:
    uk.. the middle bit
    tr3 is the relay driver transistor .
    it appears to connect the relay ground when the base is supplied its current . probably or volt . at least 600mv or it wont turn on .
    top pin cn14 looks to be ground .
     
  6. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    22,434
    Location:
    uk.. the middle bit
    p.s when you connected the relay backwards you may have damaged d5
     
  7. toxcrusadr

    toxcrusadr AK Subscriber Subscriber

    Messages:
    27,455
    Location:
    Central Missouri
    Well switching the ground instead of the hot side of the relay would explain the setup. Being a relative noob I would have guessed they would switch the +12V.

    So do I need to check that transistor? It's a tiny TO92 type. I looked up the datasheet but I could not discern how to identify the leads.

    I really appreciate the help, I feel like I'm close.
     
  8. toxcrusadr

    toxcrusadr AK Subscriber Subscriber

    Messages:
    27,455
    Location:
    Central Missouri
    Transistor is labeled
    C102
    M029

    Google tells me this may be a 2SC102.
    On the 'flat' side of the transistor (front) the leads are from L to R: E, C, B?
     
  9. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    22,434
    Location:
    uk.. the middle bit
    2SC102 is an old t036 cased one ..
     
  10. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    22,434
    Location:
    uk.. the middle bit
    [​IMG] circuit as far as i can tell is like this .
     
  11. toxcrusadr

    toxcrusadr AK Subscriber Subscriber

    Messages:
    27,455
    Location:
    Central Missouri
    Last edited: Jun 11, 2017
  12. toxcrusadr

    toxcrusadr AK Subscriber Subscriber

    Messages:
    27,455
    Location:
    Central Missouri
    That circuit basically makes sense to my simple mind, except I'm not sure what the diode does.

    What would you suggest as the next troubleshooting step?
     
  13. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    22,434
    Location:
    uk.. the middle bit
    i would get all the voltages at the transistor .
     
  14. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    22,434
    Location:
    uk.. the middle bit
  15. toxcrusadr

    toxcrusadr AK Subscriber Subscriber

    Messages:
    27,455
    Location:
    Central Missouri
    B, C, E then. OK.

    E to C 66 mv
    E to B 50 mV
    C to B 12V
     
  16. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    22,434
    Location:
    uk.. the middle bit
    using pin 1 cn14 as negative reference point get b c e voltages .
     
  17. toxcrusadr

    toxcrusadr AK Subscriber Subscriber

    Messages:
    27,455
    Location:
    Central Missouri
    See my post above yours, that's what I did and did use that pin for reference.
     
  18. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
    22,434
    Location:
    uk.. the middle bit
    black meter probe needs to stay on pin 1 cn14 . then in turn get b c e voltages .
    this way will make more sense
     
  19. toxcrusadr

    toxcrusadr AK Subscriber Subscriber

    Messages:
    27,455
    Location:
    Central Missouri
    Pin 1 IS one of the transistor leads I gotta look up which again.
     
  20. markthefixer

    markthefixer On Hiatus, dealing with Dad's estate full time Subscriber

    Messages:
    20,497
    Location:
    Bensenville,Illinois
    Pete, you were on the right track. But guys I suspect we don't have to dive that deep. Go with my preferred method below, and we'll only dive deep if a transistor is defunct. Our energies are better spent figuring out if it's just a humidity sensor (board) or the brain board failing to turn on the compressor request signal.

    Tox: the diode is across the relay coil - when the relay releases, the magnetic field collapses making a "flyback" pulse that can hurt the transistor, the diode shunts that energy and keeps the voltage of the pulse down below what the transistor can tolerate.
    Your diagram above is essentially correct, with both the resistors internal to the transistors. The center terminal of the 3 terminal regulatror IC's is ground.
    The transistor is NPN, high gain, 2 internal resistors, and laid out with a center collector (relay coil connection), and the grounded emitters are the tip-off for finding the bases.

    To test those tr's, tr1, tr2, tr3:
    two of the three transistors control the other relays which are the fan (which i think is orange hi (tr2 cn17) and black lo (tr1, cn16), so AS A LAST RESORT tr1 or tr2 it could be swapped with tr3. TR3 is purposely installed 180 degrees off of the other two's alignment with their flats. the transistors have internal resistors, one limits the base current, so some of the troubleshooting worries I had have evaporated.

    what are the numbers on IC1 and IC2? I think IC 1 has a 12 in it, while IC2 has a 05 in it. For 12v for the relay drive and 5v for the logic board..

    A top picture (clearer) of the board would be good.

    edit: pin 3 changed to pin 2, Tox caught the error - it's the orange highlighted trace.
    I prefer this method of quickly testing the board.
    You could disconnect CN14 from the brain board, and trigger pins 5 6 or 7 on THIS board using a jumper to +5v (pin 3 2 of CN14 or better yet the + of C3) to engage each relay separately, but NOT any two at a time, the high and low on at the same time for the fan might damage it. At this point the problem is not on this board, as long as +5v is going out to the brain. While the +12v is available, the wiring diagram you posted doesn't take it to the brain.

    If the individual fakes of those relays work, the board is GOOD, and no further time needs to be expended upon it.
    The layout and pretty much everything on the board makes sense to me - I figure I have it figured out. Trust me.

    I even understand why they used TWO boards in the unit - the AC control board (UL approval etc) and the brain board (low voltage - no approval needed and can be changed on a whim while the UL approved board needs to be reapproved).


    upload_2017-6-12_1-37-22.png
     
    Last edited: Jun 15, 2017

Share This Page