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Viewsonic 17 power issue

Discussion in 'Electronic Repair' started by [email protected], Sep 16, 2008.

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  1. Guest

    I have a Viewsonic 17, model 1782, Chassis series 17HV2, computer
    monitor - made by Matsushita 1994.
    Was working fine - cut it off, transported to office - carefully!
    Turned on - power LED came on for about 1 sec then faded off.
    When it goes off, there is a sound like the degaussing coil
    energizing. I pulled that connection and it does the same thing.

    Seems like there is a load on one of the rails causing the whole
    switcher to shut down. All caps (that I can see without removing the
    main PCB) look OK - no buldging. Nothing smoking, smelling, or
    burning.

    I have a schematic for a 17G but I can't find the power LED on it.
    Some connector designations match - like the degaussing coil
    connector. So it is probably not exactly a 1782.

    Any experience or how to troubleshoot hints??

    thanks

    bill
     
  2. Guest

    Thanks SC - it is definitely internal to the monitor.
    I guess I'll have to start by trying to figure out how to disconnect
    loads.
    I was looking for the feed to the LED to see if I could eliminate some
    B+ lines. It is probably the 5V, but I thought finding it might give
    me a clue. I was thinking the 175V since the higher voltages are
    probably the last ones to come up. I don't know where else that goes
    but it does feed the degaussing crt. thru a couple of triacs.
    Strange implementation.
    It has to set a while, or if I read resistance on the power plug it
    may discharge something, so that the next time I power on the LED
    comes on for a sec. Otherwise it does not come on everytime I power
    on.

    I guess the first thing to pull is the HOT.

    thanks again
     
  3. Anon

    Anon Guest

    Bill,

    Something to consider - unsupported refresh rates or resolutions can result
    in the symptom described. Whenever changing out different spec monitors,
    change the display to the most basic, VGA 640x480, before disconnecting the
    old monitor.

    FWIW, my old Viewsonic 17 failed on a number of different resolutions,
    starting with the high refresh rates, over the course of two years, before
    finally failing completely on any setting.

    Scott
    in Dunedin, FL
     
  4. Guest

    OK, I pulled the HOT heat sink with devices.


    A 2SC4288A, I assume is the HOT, is shorted all the way around.

    An IRFPF40, which may not be a transistor, is short on what would
    normally be base to collector. Open emitter to base. It is an
    International Rectifier device (hence IR...).

    I know there are components like caps that can blow these out -
    anybody have a familiarity with this one?


    The unit was working at home with the computer at the resolution that
    I have run forever. So it isn't an incompatible issue. The monitor
    will also take just ablut anything the adapter can give it.
     
  5. Guest

    The spec sheet for the IRFPF40 does not indicate the pinout.
    It is a "1000V Single N-Channel HEXFET Power MOSFET in a TO-247AC
    package"

    Is it left to right, 1-2-3 = S-D-G or G-D-S??
    the ohms 2-3 is - to + = 100 and + to - = 1k
    1-2 either way is infinite.

    thx
     
  6. Hi!
    That is exactly where I'd start. Get those caps out of there and test them,
    or just replace them and the bad parts. Then bring the power up carefully,
    and I'll bet you're back in business again.

    If the monitor had a good picture, it should be worth repairing.

    William
     
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