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HP W2408 No Power

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    #21
    Re: HP W2408 No Power

    Originally posted by kjspylite View Post
    C854
    175-195 Vdc fluctuating
    ...
    C872
    10-15 Vdc fluctuating

    C884
    0.2-1 Vdc
    Looks like the power supply has a problem starting up. There's a few things that can cause this:

    1) Shorted output diode(s)
    To see if this is the problem, check schottky diodes D853 and D854. First turn OFF and unplug the monitor. Next, let's say you're checking D853 - put red (+) multimeter probe on middle pin (pin 2) of diode D853 and black (-) probe on either outer pins (pin 1 or 3). Measure the resistance with your multimeter and report back what you find. Repeat for D854.

    2) Bad component in the start-up circuitry
    To see if this is the problem check the following items:
    - Check that resistor R855 (next to the big yellow transformer) is not open circuit or reading much higher in value than what it should be (check color code on it)
    - Verify that diode D852 (it's close to R855) is not shorted. See what value it gives you with the diode setting on your multimeter.
    - Test electrolytic caps C872 and and C884 with an ESR meter. If you do not have an ESR meter, then replace those caps. Make sure the new caps have identical voltage and capacitance values.

    Comment

      #22
      Re: HP W2408 No Power

      And of course, momaka has already documented all the other possible problems.
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      Comment

        #23
        Re: HP W2408 No Power

        Thanks. Ill try your suggestions and will report back my findings.

        Comment

          #24
          Re: HP W2408 No Power

          I replaced C872 and when I gave the board power, it sparked and appears to have blown the fuse. It gave me a pretty good scare. I think I'm in over my head and will likely trash the monitor. Not sure exactly how dangerous this stuff is, but I'm not willing to risk an eyeball or worse over it. Many thanks to those who tried to help me. I might not have fixed it, but I still learned quite a bit just reading your responses and poking my nose around the electronics.
          Attached Files
          Last edited by kjspylite; 06-27-2012, 07:44 PM.

          Comment

            #25
            Re: HP W2408 No Power

            Originally posted by kjspylite View Post
            I replaced C872 and when I gave the board power, it sparked and appears to have blown the fuse. It gave me a pretty good scare. I think I'm in over my head and will likely trash the monitor.
            Did you put in the cap properly observing correct polarity (positive and negative)? If not, the cap will go pop.

            Rather than trash it, give or sell it. Others may be able to repair it?
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            Comment

              #26
              Re: HP W2408 No Power

              Originally posted by kjspylite View Post
              I replaced C872 and when I gave the board power, it sparked and appears to have blown the fuse. It gave me a pretty good scare. I think I'm in over my head and will likely trash the monitor. Not sure exactly how dangerous this stuff is, but I'm not willing to risk an eyeball or worse over it. Many thanks to those who tried to help me. I might not have fixed it, but I still learned quite a bit just reading your responses and poking my nose around the electronics.
              Safety glasses are a must when testing electronics. I use them even when testing computers sometimes (if they have their side open, that is).

              Looks more like you shorted the board due to improper placement or perhaps a loose screw or solder shorted the live to neutral.

              Check that you put the cap in the right way, as retiredcaps suggested.

              And if you do decide to give up, there's always craigslist. When I have stuff to give out, I usually put them on the curb and put a "curb alert" post in the free section. Works rather well.
              Last edited by momaka; 06-29-2012, 12:02 AM.

              Comment

                #27
                Re: HP W2408 No Power

                Originally posted by momaka View Post
                Safety glasses are a must when testing electronics. I use them even when testing computers sometimes (if they have their side open, that is).

                Safety glasses are also good during soldering. Nothing like getting hot solder in the eye

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