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2007FPb turns off after 0-3 seconds

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    #1

    2007FPb turns off after 0-3 seconds

    I picked up a Dell 2007FPb from the trash pile at work with the sticky note "BAD; power fails"

    I opened it up and noticed it had a blown fuse. I replaced the fuse, and now it powers on and the LCD displays the Dell startup splash. The backlight works, so the inverter appears to be ok. However, after a seemingly random time (longest I saw was ~3 seconds), it turns off; not just the screen, the power/status LEDs as well.

    I visually inspected the power supply board and there don't appear to be any bad capacitors or other components (although I suspect that a capacitor is indeed the problem).

    Any suggestions on what to try?
    Tags: None
    #2
    Re: 2007FPb turns off after 0-3 seconds

    Originally posted by mabrowning View Post
    I picked up a Dell 2007FPb from the trash pile at work with the sticky note "BAD; power fails"

    I opened it up and noticed it had a blown fuse. I replaced the fuse, and now it powers on and the LCD displays the Dell startup splash. The backlight works, so the inverter appears to be ok. However, after a seemingly random time (longest I saw was ~3 seconds), it turns off; not just the screen, the power/status LEDs as well.

    I visually inspected the power supply board and there don't appear to be any bad capacitors or other components (although I suspect that a capacitor is indeed the problem).

    Any suggestions on what to try?
    The second step is to measure the output voltage of the power supply. Often the voltages are labeled.

    The third thing to do is to take pictures of the front and back of both boards. Read just about any thread where retiredcaps made teh second post and you will see suggestions on taking good pictures.

    The first step is to answer the question 'Was this test done with a signal applied?'

    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

      #3
      Re: 2007FPb turns off after 0-3 seconds

      I snapped pictures of the front and back of the power supply board. When I listen closely, I do hear a small clicking at approximately 10Hz. The output line is holding steady at 18.9V.

      No signal is applied.

      Looking closer at the board, several inductors (L610, L612, and L701) do appear to be leaking...
      Attached Files
      Last edited by mabrowning; 08-25-2010, 10:01 PM.

      Comment

        #4
        Re: 2007FPb turns off after 0-3 seconds

        Originally posted by mabrowning View Post
        No signal is applied.

        Looking closer at the board, several inductors (L610, L612, and L701) do appear to be leaking...
        Apply a source and retest. Most monitors will turn off with "no signal" and go into sleep mode without a source. If that still fails, post a picture of all your boards (inverter, and logic).

        That could be glue used in the manufacturing process to hold the inductors in place until soldering or final assembly? It may have been white but turned brown due to age and/or heat?
        --- begin sig file ---

        If you are new to this forum, we can help a lot more if you please post clear focused pictures (max resolution 2000x2000 and 2MB) of your boards using the manage attachments button so they are hosted here. Information and picture clarity compositions should look like this post.

        We respectfully ask that you make some time and effort to read some of the guides available for basic troubleshooting. After you have read through them, then ask clarification questions or report your findings.

        Please do not post inline and offsite as they slow down the loading of pages.

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        Comment

          #5
          Re: 2007FPb turns off after 0-3 seconds

          Originally posted by mabrowning View Post
          I snapped pictures of the front and back of the power supply board. When I listen closely, I do hear a small clicking at approximately 10Hz. The output line is holding steady at 18.9V.

          No signal is applied.

          Looking closer at the board, several inductors (L610, L612, and L701) do appear to be leaking...
          Excellent pictures.

          18.9 volts is an unusual voltage. I'd like pictures of the logic card - front and back. I'd suggest doing minimal testing; I suspect a regulator on the logic card is shutting down due to overheating.

          That's an illusion. Nothing in an inductor to leak.

          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

            #6
            Re: 2007FPb turns off after 0-3 seconds

            Ok, I tried with a source attached, just in case, and it still exhibited the same symptoms. It doesn't look like a sleep mode power-off, it happens mid-startup.

            I was thinking that R615 was shorted, but the resistor code(Br Gr Slv) says its .15 Ohms...

            Hmm... since inductors probably don't have electrolytic fluid in the, you're probably right about the glue.

            I'll post pictures of the other boards, too. I guess since there's a steady ~20V, it might not be the power supply...

            Not sure if this is relevant, but at the positive terminal of D606, at the solid black silkscreen boundary, there is steady AC~0.536V.

            Comment

              #7
              Re: 2007FPb turns off after 0-3 seconds

              Originally posted by mabrowning View Post
              I'll post pictures of the other boards, too. I guess since there's a steady ~20V, it might not be the power supply...
              We are talking 18.9 or 20V DC right? Also, on which pins?

              I have a LCD with secondary voltages of 5V and 19V DC.

              If you are getting stable secondary DC voltages your power supply is likely working okay.
              --- begin sig file ---

              If you are new to this forum, we can help a lot more if you please post clear focused pictures (max resolution 2000x2000 and 2MB) of your boards using the manage attachments button so they are hosted here. Information and picture clarity compositions should look like this post.

              We respectfully ask that you make some time and effort to read some of the guides available for basic troubleshooting. After you have read through them, then ask clarification questions or report your findings.

              Please do not post inline and offsite as they slow down the loading of pages.

              --- end sig file ---

              Comment

                #8
                Re: 2007FPb turns off after 0-3 seconds

                I was doing testing on it with all the boards connected, but with the panel disconnected. At first, I heard a whine every ~3-4 seconds, corresponding to the previously witnessed power off. Right before the whine, the voltage on the 3.3V secondary line would drop and then recover. The 19V (18.9V) stayed constant the whole time.

                However, while I was testing, this behavior stopped. The 3.3V stayed constant. I tried to get it to repeat by unplugging from mains, draining the big cap, and replugging, but no avail.

                On a hunch, I reconnected the panel, and lo and behold, it works! Its been running for 20 minutes so far, no problem.

                I don't think I did anything... all I was doing was pressing on solder pads testing with the multimeter. Maybe I pressed a loose one back tighter?

                Anyway, thanks a bunch for helping me out. If it starts turning off again, I'll probably come on back.

                Comment

                  #9
                  Re: 2007FPb turns off after 0-3 seconds

                  Well, we just had a dip... but it came right back. I guess I'll just "monitor" it(hehe) and see how frequently this happens and decide if its worth the effort to correct.

                  Edit: another one, within a few minutes.... looks like I declared it fixed too soon.

                  Tomorrow I'll get pictures of the logic board and hopefully you can help me pinpoint the regulator(s) and how to test them.

                  Comment

                    #10
                    Re: 2007FPb turns off after 0-3 seconds

                    Originally posted by mabrowning View Post
                    Well, we just had a dip... but it came right back. I guess I'll just "monitor" it(hehe) and see how frequently this happens and decide if its worth the effort to correct.

                    Edit: another one, within a few minutes.... looks like I declared it fixed too soon.

                    Tomorrow I'll get pictures of the logic board and hopefully you can help me pinpoint the regulator(s) and how to test them.
                    The symptoms you describe are classic for a bad solder joint. They are easy to fix once found. The problem is finding it....

                    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

                      #11
                      Re: 2007FPb turns off after 0-3 seconds

                      Originally posted by PlainBill View Post
                      The symptoms you describe are classic for a bad solder joint. They are easy to fix once found. The problem is finding it....

                      PlainBill
                      Definitely agree. I was having a similar issue with the same monitor. Went ahead and put the board in my reflow oven and the problem was solved!

                      Comment

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