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Dell P991 Ultrascan Monitor

Discussion in 'Troubleshooting and Repair' started by WVDon, Jun 1, 2011.

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  1. WVDon

    WVDon

    2
    0
    Jun 1, 2011
    My excellent P991 monitor has started randomly degaussing itself on an average of 10 - 15 seconds between degaussing.

    I have no service manual but wonder if this is a problem I can fix at home? Can anyone give me some information on this problem?

    Don
     
  2. davenn

    davenn Moderator

    13,655
    1,888
    Sep 5, 2009
    Hi Don
    Welcome :)

    I dont know that particular monitor, naturally assuming its a CRT type.
    its probable that the 3 pin (usually 3pin rarely 2 pin) PTC Thermistor has/is failing
    I used to see it periodicaly in my TV servicing days

    Follow the degaussing coil wires back from the screen to the circuit board
    it will most likely head back to the early part of the PSU.
    The degaussing voltage is usually the mains voltage 110 or 220-240 whatever where you live
    Have a look for something like this....

    [​IMG]

    note particularly the 3 pin black rectangular ones, they also are commonly cylindrical and blue or white

    see how ya go finding it
    report back with maybe a clear/sharp photo ofthat area of the cct board and we can identify it for you :)

    cheers
    Dave
     

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    Last edited: Jun 3, 2011
  3. WVDon

    WVDon

    2
    0
    Jun 1, 2011
    WOW! I didn't expect such a quick response.

    The Dell Ultrascan P991 has Trinitron printed on the lower left corner of the faceplate. I suspect it is a Sony product. It is indeed a CRT monitor.

    I've looked at the case and it appears that I need to place it on its faceplate and remove four screws at each corner. Other than that it appears the case is held together by magic.

    I will have a spine medical procedure scheduled Friday morning and am not able to lift/move anything greater than 10 pounds. Which means I will need to find an available friend with strong arms and back to wrestle it out of a box and on a table so I can open the case. This may take several days. In the meantime, I have an old ViewSonic A70 that works--not as good as the P991 though.

    From what you say, I assume the thermistor is acting like a switch--closed when the unit is first turned on and then opens after the unit is degaussed at turn-on. The failure then would be the thermistor closing randomly. There is the sound of a relay clicking at the beginning of the degauss--probably actuating the degauss circuitry and powering the degauss coils. It appears the voltage on the degauss coils is modulated as it strongly wiggles and distorts the picture at the beginning gradually returning the picture to normal geometry.

    Thanks for the info. I'll use it as soon as I can.


    Don
     
    Last edited: Jun 2, 2011
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