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    Dell 24" LCD, bad inverter or light - testing?

    Hi all,

    I have an older (circa 2005) 24" Dell LCD that powers on, but has no backlight.
    I have confirmed that the screen is functional with a bright light.
    I pulled it apart and have the power board on my bench, photo attached.
    Larger photos are available if anyone needs to see anything specific.
    How do I go about testing the inverter portion of the board and/or the CCFL to determine which is faulty?

    Thanks in advance,
    -Mike
    Attached Files

    #2
    Re: Dell 24" LCD, bad inverter or light - testing?

    Originally posted by Elmojo View Post
    Hi all,

    I have an older (circa 2005) 24" Dell LCD that powers on, but has no backlight.
    I have confirmed that the screen is functional with a bright light.
    I pulled it apart and have the power board on my bench, photo attached.
    Larger photos are available if anyone needs to see anything specific.
    How do I go about testing the inverter portion of the board and/or the CCFL to determine which is faulty?

    Thanks in advance,
    -Mike
    Okay, let's start with a few things:

    It would help if you provided a model number for the monitor because some good citizen out there may have a schematic for it. Or better yet, someone may have already worked on the same monitor.

    The photo is good, but we can't do any closeups to tell you where to perform test measurements. Also, post a photo of the bottom of the board. See link:

    https://www.badcaps.net/forum/showthread.php?t=1868


    The way it generally works is that there are two voltages: 5 volts to power the logic card and LCD panel and 12 volts to power the inverter section. Looks like you have the 5V. As for the 12V, there are generally two duo diode paks mounted on the heatsink, one for 5V and the other for 12V. You will need to check the output of these paks to verify the 12V. If you don't know how to do this, then please provide the part numbers of the middle heatsink with 4 mounted components.

    Also, many times the input to the inverter section is fuse protected. The fuse can be mounted on the top of the board, or be a surface mount fuse on the bottom.

    There's also a chance that some of the caps are bad, but some are very difficult to see because they are covered by the white glue.

    Possibly, there are mosfets (part of the inverter circuit) on the bottom of the board that are burned out.

    Finally, a CCFL tube may have gone bad. Did you notice any of flash of light when you first turned on the monitor?
    Last edited by jetadm123; 10-05-2010, 08:55 PM.

    Comment


      #3
      Re: Dell 24" LCD, bad inverter or light - testing?

      I didn't post a photo of the bottom because there are no components on the back side, just solder traces and pads.
      The monitor was already nonfunctional and partially disassembled when I got it, so I don't have the exact model number.
      I also don't know what behavior it exhibited before total failure, for the same reason.
      Thanks for the info, I'll check it out this evening and report back.

      Comment


        #4
        Re: Dell 24" LCD, bad inverter or light - testing?

        Originally posted by Elmojo View Post
        I didn't post a photo of the bottom because there are no components on the back side, just solder traces and pads.
        The monitor was already nonfunctional and partially disassembled when I got it, so I don't have the exact model number.
        I also don't know what behavior it exhibited before total failure, for the same reason.
        Thanks for the info, I'll check it out this evening and report back.
        I second what jetadm123 said. The lack of a model number is not a show-stopper, but the lack of adequate pictures is. Your statement that there are no components on the back side either indicates the board was stripped of vital components such as the inverter controller, or you are not familiar with SMT components. Follow the links in my signature for information on taking pictures. This is one of those cases where size is important - as close to the 2000 x 2000 limit as possible makes a great deal of difference.

        Also, most boards have some sort of orientation. It's a minor point, but following that orientation makes it easier to read the legends.

        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


          #5
          Re: Dell 24" LCD, bad inverter or light - testing?

          PlainBill! Great to see you're still around here.
          I'll post better pictures when I get home, but I'm fairly sure there are no components on the back of the board, SMT or otherwise.
          -Mike

          Comment


            #6
            Re: Dell 24" LCD, bad inverter or light - testing?

            I did a quick search of the power board model number and it looks like this board goes into a Dell 2005FPW. If you look at the photo in the link below, post #10, you will see what PlainBill and myself were talking about. There are 5 black rectangular (q317-320 and u301) components. If you're missing these, then it's another ball game altogether.


            https://www.badcaps.net/forum/showth...hlight=2005fpw

            Comment


              #7
              Re: Dell 24" LCD, bad inverter or light - testing?

              That model number sounds right, and that does look like my board, but I swear I don't remember seeing all those components on the back side!
              Oh, well, they say the mind is the first to go, right?!
              So, assuming this is my board, where do I start testing?

              Comment


                #8
                Re: Dell 24" LCD, bad inverter or light - testing?

                Originally posted by Elmojo View Post
                That model number sounds right, and that does look like my board, but I swear I don't remember seeing all those components on the back side!
                Oh, well, they say the mind is the first to go, right?!
                So, assuming this is my board, where do I start testing?
                A good starting point would be a 2000 x 2000 pixel picture of the bottom side of the power supply / inverter board. Also, the part number of the inverter controller would be much appreciated.

                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


                  #9
                  Re: Dell 24" LCD, bad inverter or light - testing?

                  Okay, new photos attached at the size requested.
                  I can do macro shots of any particular parts of the board if needed.
                  I'm not sure what part of this is the inverter controller, but all the relevant numbers should be visible in the photos.
                  Thanks again,
                  -Mike
                  Attached Files

                  Comment


                    #10
                    Re: Dell 24" LCD, bad inverter or light - testing?

                    Originally posted by Elmojo View Post
                    Okay, new photos attached at the size requested.
                    I can do macro shots of any particular parts of the board if needed.
                    I'm not sure what part of this is the inverter controller, but all the relevant numbers should be visible in the photos.
                    Thanks again,
                    -Mike
                    The pictures are better, and the components are there, but I can't make out the part number or even the identifier. The inverter controller is the 20 pin IC on the back. What is the part number?

                    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: Dell 24" LCD, bad inverter or light - testing?

                      Bill, I'll be darned if I can read that number!
                      It looks like it has some sort of residue on it, but cleaning doesn't seem to make any difference.
                      I attached the best photo I can get. The lighting on that thing is a bear.
                      -Mike
                      Attached Files

                      Comment


                        #12
                        Re: Dell 24" LCD, bad inverter or light - testing?

                        Originally posted by Elmojo View Post
                        Bill, I'll be darned if I can read that number!
                        It looks like it has some sort of residue on it, but cleaning doesn't seem to make any difference.
                        I attached the best photo I can get. The lighting on that thing is a bear.
                        -Mike
                        Try running a yellow hi-liter over the chip see if that helps
                        Al.
                        Whatever I do, I consider it a success, if in the end I am breathing, seeing, feeling and hearing!

                        Comment


                          #13
                          Re: Dell 24" LCD, bad inverter or light - testing?

                          If anything, that made it worse.
                          I'm pretty sure mine is the same board as the one referenced in post #6, if that helps.

                          Comment


                            #14
                            Re: Dell 24" LCD, bad inverter or light - testing?

                            Okay, I think I got it. Some monkeying around with the lighting and a little creative photoshop manipulation, and I think I can read it.
                            I read it as:
                            OZL68GN
                            F28300.3T
                            0537B1
                            Check the photo and see if you agree.
                            Attached Files

                            Comment


                              #15
                              Re: Dell 24" LCD, bad inverter or light - testing?

                              Originally posted by Elmojo View Post
                              Okay, I think I got it. Some monkeying around with the lighting and a little creative photoshop manipulation, and I think I can read it.
                              I read it as:
                              OZL68GN
                              F28300.3T
                              0537B1
                              Check the photo and see if you agree.
                              That's the part number, but I'm having problems finding a datasheet for it. The closest I could come was the schematic for an inverter using it.

                              Check the voltage on pin 5 of the IC when the backlight should be on. It should be about 5 volts.

                              PlainBill
                              Attached Files
                              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


                                #16
                                Re: Dell 24" LCD, bad inverter or light - testing?

                                Cool, thanks Bill.
                                I'll check that out this evening when I get home.

                                Comment


                                  #17
                                  Re: Dell 24" LCD, bad inverter or light - testing?

                                  Hi Bill,
                                  I'm so sorry for the long delay. I haven't forgot about this, but I've been swamped with work and have had no time for extra projects.
                                  I opened up the PDF and tried to figure which one is pin 1 on my board.
                                  Mine doesn't have the half-circle shape on one end, but it does have an indent. Is that pin 1?
                                  Also, what's the safest way to power the board and put it into the "on" state?
                                  I can plug in the AC cable to the board, but I don't have a way of turning it on without at least partially re-assembling the unit.
                                  Any ideas?
                                  Thanks,
                                  Mike

                                  Comment


                                    #18
                                    Re: Dell 24" LCD, bad inverter or light - testing?

                                    Originally posted by Elmojo View Post
                                    Hi Bill,
                                    I'm so sorry for the long delay. I haven't forgot about this, but I've been swamped with work and have had no time for extra projects.
                                    I opened up the PDF and tried to figure which one is pin 1 on my board.
                                    Mine doesn't have the half-circle shape on one end, but it does have an indent. Is that pin 1?
                                    Also, what's the safest way to power the board and put it into the "on" state?
                                    I can plug in the AC cable to the board, but I don't have a way of turning it on without at least partially re-assembling the unit.
                                    Any ideas?
                                    Thanks,
                                    Mike
                                    The small circle on the top identifies pin 1. Viewed from the top, the pins are numbered counter-clockwise, so with pin 1 in the lower left corner, the pins are numbered 1 2 3 4 5, etc.

                                    As you say, you'll have to partially reassemble it. What I do is lay the LCD panel face down on a slightly cushioned surface, lay a piece of static free pink foam on the back side of the panel, then reassemble the power supply and logic card on top of that. The pink foam is used to protect motherboards, etc when they are placed in static shielding bags; in a pinch you can use a piece of cardboard. Don't use styrofoam!!!

                                    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


                                      #19
                                      Re: Dell 24" LCD, bad inverter or light - testing?

                                      okay, I see pin 5 now. I have some anti-static bags and foam around here, I'll rig up something. So i guess I just plug it in and try to turn on the unit, then measure the pin 5 voltage? If I get 5v on pin 5, what then?

                                      Comment


                                        #20
                                        Re: Dell 24" LCD, bad inverter or light - testing?

                                        Originally posted by Elmojo View Post
                                        okay, I see pin 5 now. I have some anti-static bags and foam around here, I'll rig up something. So i guess I just plug it in and try to turn on the unit, then measure the pin 5 voltage? If I get 5v on pin 5, what then?
                                        Also check pin 3. Then we try to figure out why the inverter isn't working.

                                        I'm not criticizing you, I certainly understand that work and family comes first. However, with the delay I've lost the details of this thread. Skimming it, I often asked myself 'Why did I ask that?' Now I'm wondering if I was smarter then.

                                        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

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