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Troubleshooting a Dehumidifier

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

  1. toxcrusadr

    toxcrusadr AK Subscriber Subscriber

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    Sorry for the slow reply, I got busy and haven't got back to this. Thanks for the analysis Mark.

    Questions:

    1) the fan does come on, just the compressor doesn't. Is your test (triggering pins 5,6, or 7 with +5V) still necessary? It seems that if the brain board is turning on the fan then +5V is going to the brain board which is the purpose of the test.

    2) "...trigger pins 5 6 or 7 on THIS board using a jumper to +5v (pin 3 of CN14 or better yet the + of C3) to engage each relay separately..." On your labeled drawing above, pin 2 is +5V and pin 3 is +12V. Are we using 5 or 12V on pins 5, 6 and 7? I believe that's 5V and pin 2....or is it 12V and pin 3? ;)

    In an earlier post it looks like I said the 12V regulator was 7812a. Seems like the other one was 7805 but I'm not at home at the moment. I can get a better pic of the top also.

    Really appreciate everyone's help. Humidity is bad and I've got an ancient 80s unit going that's on its last leg!
     
  2. markthefixer

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

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    more pix of that board unnecessary for now.

    You caught my pin 3 / pin 2 error. It's pin 2, and 5 volts. 12volts might be too "hot".

    #1. test is necessary - just because the fan works doesn't mean the works aren't jammed up for the compressor on the relay board
    The TEST is that we need to see the compressor operate from a 5v logic signal on pin 5,
    to verify TR3 is ok, and even to the level that the 12v substitution you used didn't hurt anything.
    Disconnecting the brain board for the test is to prevent damage to the brain board from the pin 5 signal being substituted.
    Pins 6 and 7 being operated successfully also tests both the board and the method in case pin 5 didn't operate.
     
    Last edited: Jun 15, 2017
  3. markthefixer

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

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    One we verify the board, then we consider why the brain isn't turning on the compressor.
    The logical first thought is the humidity sensor on a separate little board.
     
  4. toxcrusadr

    toxcrusadr AK Subscriber Subscriber

    Messages:
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    Location:
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    Got it. I'm away for the weekend so it looks like it'll be early next week before I can get to it. Just so you know I'm not blowing off the help. :biggrin:

    The humidity sensor is indeed on a tiny board of its own, I had to unscrew it from the front cover of the machine to remove the cover.
     
  5. markthefixer

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

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    Gotcha, no problem. slow but steady wins the race.
    Tell ya whut, PM me to wake me up when you are continuing the thread, then I won't be forever checking back in to see if anything's posted new.
     
  6. markshan

    markshan Sir Thrift a Lot Subscriber

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    Last edited: Jun 22, 2017
  7. markthefixer

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

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    First - my suggestion: new thread, this is an active thread.
    second - try a different GFI - they can get squirrely.
     
  8. toxcrusadr

    toxcrusadr AK Subscriber Subscriber

    Messages:
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    Location:
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    Sorry for the long delay when such expert help has been offered. One thing after another.

    I did the requested test: disconnected CN14, jumpered +5V to each of the fan and compressor relay pins (5,6,7) in turn. Worked in all three cases - fan at each speed and compressor all turned on. So it appears there is no problem on this board, and the problem is either in the brain board or the humidity sensor.

    Awaiting further instructions, Houston. :cool:
     
  9. toxcrusadr

    toxcrusadr AK Subscriber Subscriber

    Messages:
    27,805
    Location:
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    Humidity sensor has a 3-wire cable to it. Besides the sensor itself on the board (which takes up 2 of the 3 pins) there is a very small dipped component connecting the remaining pin to one side of the sensor. No markings on it that I can see.

    I looked up how these sensors work, apparently a capacitor that changes value as moisture enters the insulating layer. So I put my meter across the two leads of the sensorand set the meter to read capacitance. Capacitance was decreasing until I breathed on the sensor and it spiked back up. It would appear this sensor has a pulse. How accurate it is, I don't know.

    I thought the other little component might be a temp sensor based on what I read. It reads 46 kohms but if I put my fingers on it the resistance begins to decrease down to about 42 k. So this might be working OK too, at least not totally dead.
     
  10. petehall347

    petehall347 the brandy coffee man Subscriber

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    is the brain board getting power ?
    what sort of power supply is it ? like switching or normal transformer etc ?
     
  11. toxcrusadr

    toxcrusadr AK Subscriber Subscriber

    Messages:
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    Yes the brain board powers up and the display and selector buttons work. There is a small transformer on the control board (the board we've been looking at).
     
  12. toxcrusadr

    toxcrusadr AK Subscriber Subscriber

    Messages:
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    If the humidity sensor works on capacitance and the temp sensor on resistance, I figured maybe a small AC voltage would be applied to the pin that is common to both. This would allow measurement of resistance and capacitance to get the temp/RH. I measured across the temp sensor with the unit powered up and got a few mV of DC but about 2V AC. I have no idea what the voltage should be but it's getting some voltage delivered to it.
     
  13. petehall347

    petehall347 the brandy coffee man Subscriber

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    a good pic of the brain board or even better a schematic or board layout should be of help .
     
  14. wlhd1610

    wlhd1610 Penny and her new friend Subscriber

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  15. toxcrusadr

    toxcrusadr AK Subscriber Subscriber

    Messages:
    27,805
    Location:
    Central Missouri
  16. toxcrusadr

    toxcrusadr AK Subscriber Subscriber

    Messages:
    27,805
    Location:
    Central Missouri
  17. toxcrusadr

    toxcrusadr AK Subscriber Subscriber

    Messages:
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    You can see the 5 control buttons across the bottom - power in the center, up and down buttons at right and left of that, fan speed selector far left, Settings button at far right.

    CN14 cable connects at left. Beepy thing at top right. Looks like most of the thing is in that big chip.

    Oh, one weird thing happened when I turned it on to take this pic. Both fan and compressor started up! The compressor hasn't been running which is what started all this. It could have something to do with disconnecting and reconnecting the humidity sensor maybe? Bad news though, the condenser coils did not get cold within a minute as they should have. So we may have a freon loss problem.
     
  18. petehall347

    petehall347 the brandy coffee man Subscriber

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    if the freon has leaked out there will a tell tale mark in the pipework . at least i think there will be .i have only worked on refrigerators . much the same thing though
     
  19. toxcrusadr

    toxcrusadr AK Subscriber Subscriber

    Messages:
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    There is some bluish copper corrosion that the water carried down into the collection tray, things are stained a little blue but that could just be from the water? What would freon leakage look like?
     
  20. petehall347

    petehall347 the brandy coffee man Subscriber

    Messages:
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    Location:
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    not sure really ..i might expect like a corrosion looking build up .
     

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