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HP 1825 Display Black Power Light Green

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    #41
    Re: HP 1825 Display Black Power Light Green

    Originally posted by jetadm123 View Post
    The purpose of the resistance check is for one purpose only: to locate a short between the S,D or G pins of the mosfet. Since mosfets are made differently than a BJT transistor, you cannot strictly use a resistance test to verify that a mosfet is good. However, in the case of a mosfet failing on an inverter, they generally will short out and that's what we're looking for. Therefore, don't expect to find a "normal" reading resistance wise. So, if you don't see a short using the suggested test methods, then move onward.
    Now here is a newbie conclusion, that as long as there is some resistance then it has not shorted out, so only a low ohm reading would indicate a bad mosfet?

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      #42
      Re: HP 1825 Display Black Power Light Green

      When replacing my caps I see that I made a mistake in measuring the height of the caps. It should read that the 470uf 25v caps are 10mm wide and 16 mm high. The two caps on the inverter are 7 mm wide and 5 mm high and 22uf 25v. Both of these caps were bad and appear to be the reason for the bad smd fuse at location F1.

      After replacing these items with some temporary caps and a temp fuse the panel lights up.

      Thanks again for everyone's help.

      Comment

        #43
        Re: HP 1825 Display Black Power Light Green

        Originally posted by printone2 View Post
        I found the F1 fuse on the inverter board and yes they are blown on both of the bad inverter boards and good on the functioning board. Now what caused it? I still have to check the mosfets.
        I have one fuse on one inverter board that is good, but how do I tell what a replacement fuse should be for two boards that the bad caps caused the fuse to blow? The fuse is located at F1 on the inverter and is an smd. I have put a temporary glass 4amp fuse in place of the blown fuse. It seems to work fine, but I am not at all sure if that is a reasonable value for the replacement. I would like to have a few standard fuses on hand. Can someone suggest some normal ones to keep around as spares as well as suggest what might be reasonable for location F1?

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          #44
          Re: HP 1825 Display Black Power Light Green

          Originally posted by printone2 View Post
          I have one fuse on one inverter board that is good, but how do I tell what a replacement fuse should be for two boards that the bad caps caused the fuse to blow? The fuse is located at F1 on the inverter and is an smd. I have put a temporary glass 4amp fuse in place of the blown fuse. It seems to work fine, but I am not at all sure if that is a reasonable value for the replacement. I would like to have a few standard fuses on hand. Can someone suggest some normal ones to keep around as spares as well as suggest what might be reasonable for location F1?
          A good picture of F1 would help. it's probably in the 2-4 amp range, but most SMD fuses have a single letter on them which identifies the rating.

          PlainBill
          For a number of reasons, both health and personal, I will no longer be active on this board. Any PMs asking for assistance will be ignored.

          Never be afraid to try something new. Remember, amateurs built the ark. Professionals built the Titanic.

          Comment

            #45
            Re: HP 1825 Display Black Power Light Green

            Originally posted by PlainBill View Post
            A good picture of F1 would help. it's probably in the 2-4 amp range, but most SMD fuses have a single letter on them which identifies the rating.

            PlainBill
            The good fuse at F1 has the letters "FT" on it.

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              #46
              Re: HP 1825 Display Black Power Light Green

              Originally posted by printone2 View Post
              The good fuse at F1 has the letters "FT" on it.
              PROBABLY a 5A fast blow. F= fast blow T=5Amp

              PlainBill
              For a number of reasons, both health and personal, I will no longer be active on this board. Any PMs asking for assistance will be ignored.

              Never be afraid to try something new. Remember, amateurs built the ark. Professionals built the Titanic.

              Comment

                #47
                Re: HP 1825 Display Black Power Light Green

                Originally posted by PlainBill View Post
                PROBABLY a 5A fast blow. F= fast blow T=5Amp

                PlainBill
                I replaced the smd fuse with SF-1206F500-2CT-ND from Digi-Key, it is a 5 amp fast smd 1206. That along with the 22uf 25v caps on the inverter made the difference. I recapped the image card and the power supply with samxon's from badcaps.net and now two of the three panels appear to work fine. The third panel has a smashed screen, but the image and power boards are fine.

                How can I use the good lamps to test problems on other panels? I seem to have read about a kit to test lamps with. Where are plans for such a kit?
                Thanks everyone.

                Comment

                  #48
                  Re: HP 1825 Display Black Power Light Green

                  Originally posted by printone2 View Post
                  How can I use the good lamps to test problems on other panels?
                  If these are good lamps, I just leave them in their lcd housing and stretch the cables from the other monitor for testing. You don't need to build anything fancy.
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                  Comment

                    #49
                    Re: HP 1825 Display Black Power Light Green

                    Originally posted by retiredcaps View Post
                    If these are good lamps, I just leave them in their lcd housing and stretch the cables from the other monitor for testing. You don't need to build anything fancy.
                    Thanks.

                    Comment

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