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    #1

    Cap Testing

    I had a friend bring over an older KDS k717 monitor that had been acting. When I hooked it up the backlight wouldn't turn on but the power light was on and I could see the LCD itself was working. After searching around I found several thread about bad caps in the power supply.

    I set out testing the caps per this site's suggestion and found that 3 of the 6 of the group in lower right corner tested bad. The resistance would go to a certain point and hold there where the other three would steadily increase until they would 0 out again on the meter. After removing one of the caps that tested "bad" I tested it off the board and it tested fine. I then removed both the other two and they test fine as well.

    Something on the board is humming pretty good when it powered on as well. Any help would be appreciated.



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    #2
    Re: Cap Testing

    Garbage caps with fake UCC vents. Replace them all and also replace any suspect caps on the logic board as well.

    Humming is probably the coil vibrating from the erratic ESR from the capacitors.
    "We have offered them (the Arabs) a sensible way for so many years. But no, they wanted to fight. Fine! We gave them technology, the latest, the kind even Vietnam didn't have. They had double superiority in tanks and aircraft, triple in artillery, and in air defense and anti-tank weapons they had absolute supremacy. And what? Once again they were beaten. Once again they scrammed [sic]. Once again they screamed for us to come save them. Sadat woke me up in the middle of the night twice over the phone, 'Save me!' He demanded to send Soviet troops, and immediately! No! We are not going to fight for them."

    -Leonid Brezhnev (On the Yom Kippur War)

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      #3
      Re: Cap Testing

      That method will not detect caps with bad ESR.
      There aren't that many there.
      Best off replacing all of them except Mr. Jumbo.
      [That's the cap on AC input, they don't fail often.]
      Mann-Made Global Warming.
      - We should be more concerned about the Intellectual Climate.
      -
      Be who you are and say what you feel, because those who mind don't matter and those who matter don't mind.
      - Dr Seuss
      -
      You can teach a man to fish and feed him for life, but if he can't handle sushi you must also teach him to cook.
      -

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        #4
        Re: Cap Testing

        those caps are HEC
        not the worst garbage one could expect, but they don't really last too long in hot LCD monitors.
        as pcbonez said.. replace all of them except the primary (the big fat 400+V) cap..

        edit: and don't forget the small startup cap (C206 ; bottom center in the pic)

        Comment

          #5
          Re: Cap Testing

          Thanks for the advise guys.

          Comment

            #6
            Re: Cap Testing

            is it my imagination, or does that mosfet in the center there look a little burned?
            Cap Datasheet Depot: http://www.paullinebarger.net/DS/
            ^If you have datasheets not listed PM me

            Comment

              #7
              Re: Cap Testing

              looks more like heatsink compound all over the place..
              Attached Files

              Comment

                #8
                Re: Cap Testing

                kinda dark spot on the left side? dosen't look like compound
                Cap Datasheet Depot: http://www.paullinebarger.net/DS/
                ^If you have datasheets not listed PM me

                Comment

                  #9
                  Re: Cap Testing

                  Still waiting on the caps to come in. That photo isn't a picture of my actual board but the same board with identical layout.

                  Comment

                    #10
                    Re: Cap Testing

                    Just an update, got the caps in and replaced and the monitor is working great. In this whole process I've pulled out some other electronics I've had crap out over the years. The next thing on my list to fix is an Antec power supply that would make the computer unstable ofter 15 minutes of use on an power supply that was 6 months old at the time. Opened it up the other day to find it has a few bulging caps.

                    Glad I came across such a useful site, great work here guy.

                    Comment

                      #11
                      Re: Cap Testing

                      Antec PSU's are frequent visitors at the soldering table.
                      Mann-Made Global Warming.
                      - We should be more concerned about the Intellectual Climate.
                      -
                      Be who you are and say what you feel, because those who mind don't matter and those who matter don't mind.
                      - Dr Seuss
                      -
                      You can teach a man to fish and feed him for life, but if he can't handle sushi you must also teach him to cook.
                      -

                      Comment

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