HP lcd L1502 15"

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  • leov
    Member
    • Mar 2011
    • 45

    #1

    HP lcd L1502 15"

    Hi guys. I am very new to this, but was hoping you would help me fix my lcd. Originally, the screen started to turn itself off randomly. I was able to restart it, but after few days it shut down and I was not able to bring it back to life. I replaced all 25V 470 uF caps on this board. They were not blown, but looked like they were starting to "inflate". (sorry, i am not sure what the proper terminology is to describe it). That did not fix the problem though. When I connect the power cable I can hear a clicking noise coming from the parts that I circled on the picture. They turn really hot if the power cable is connected. Would someone please tell me what I should do next? How do I go about testing the other components on the board? Thank you.
    Attached Files
  • sabre504
    Badcaps Veteran
    • May 2010
    • 449
    • United Kingdom

    #2
    Re: HP lcd L1502 15"

    Hi did you test the transistors that you have arrowed (probably 5707 or 5706 markings on them )
    Also did you resolder the 4 x transformers

    If you check threads that deal with Dell 172 monitors they have the same type of board and have the same symptoms

    Comment

    • PlainBill
      Badcaps Legend
      • Feb 2009
      • 7034
      • USA

      #3
      Re: HP lcd L1502 15"

      Originally posted by leov
      Hi guys. I am very new to this, but was hoping you would help me fix my lcd. Originally, the screen started to turn itself off randomly. I was able to restart it, but after few days it shut down and I was not able to bring it back to life. I replaced all 25V 470 uF caps on this board. They were not blown, but looked like they were starting to "inflate". (sorry, i am not sure what the proper terminology is to describe it). That did not fix the problem though. When I connect the power cable I can hear a clicking noise coming from the parts that I circled on the picture. They turn really hot if the power cable is connected. Would someone please tell me what I should do next? How do I go about testing the other components on the board? Thank you.
      This is a classic example of the problems with these monitors. As sabre504 said, replace both transistors (2SC5707). Also resolder all pins on the 4 inverter transformers. Just for luck, I'd also replace the cap that was clicking.

      What brand and series capacitors did you use as replacements for the bulging caps?

      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

      • leov
        Member
        • Mar 2011
        • 45

        #4
        Re: HP lcd L1502 15"

        Originally posted by sabre504
        Hi did you test the transistors that you have arrowed (probably 5707 or 5706 markings on them )
        Also did you resolder the 4 x transformers

        If you check threads that deal with Dell 172 monitors they have the same type of board and have the same symptoms
        Hi sabre, Thank you for replying to my post. I appreciate your help. The transistors are 5707. How do I go about testing them? I have very limited understanding of these things. I did not resolder the transformers.

        Comment

        • leov
          Member
          • Mar 2011
          • 45

          #5
          Re: HP lcd L1502 15"

          Hi PlainBill,

          Thanx for taking time to look into this for me. I used united chemi-con caps from Digi-key.


          Also, I found out that the problem occurs when I connect little circuit board that has VGA connector on it. If its not connected, there is no clicking heard on the big board.

          Comment

          • Th3_uN1Qu3
            Believe in
            • Jul 2010
            • 6031
            • Romania

            #6
            Re: HP lcd L1502 15"

            That's the logic board. It's kinda obvious that it won't do it without the logic board connected, since the logic is what instructs the inverter to turn on.
            Originally posted by PeteS in CA
            Remember that by the time consequences of a short-sighted decision are experienced, the idiot who made the bad decision may have already been promoted or moved on to a better job at another company.
            A working TV? How boring!

            Comment

            • leov
              Member
              • Mar 2011
              • 45

              #7
              Re: HP lcd L1502 15"

              So i guess it would be safe to assume that the logic board is working fine.

              Comment

              • Th3_uN1Qu3
                Believe in
                • Jul 2010
                • 6031
                • Romania

                #8
                Re: HP lcd L1502 15"

                Yes. Your problem is in the inverter area. For now, take out the 5707 transistors and measure them with your multimeter set to 200 ohm scale. If any leg combinations read 0 ohms the transistors are bad and need to be replaced.
                Originally posted by PeteS in CA
                Remember that by the time consequences of a short-sighted decision are experienced, the idiot who made the bad decision may have already been promoted or moved on to a better job at another company.
                A working TV? How boring!

                Comment

                • leov
                  Member
                  • Mar 2011
                  • 45

                  #9
                  Re: HP lcd L1502 15"

                  Thank you, I will try doing that as soon as i get a chance.

                  Comment

                  • retiredcaps
                    Badcaps Legend
                    • Apr 2010
                    • 9271

                    #10
                    Re: HP lcd L1502 15"

                    Originally posted by Th3_uN1Qu3
                    For now, take out the 5707 transistors and measure them with your multimeter set to 200 ohm scale.
                    I usually test components "in circuit". If the readings are suspicious, then I desolder and measure "out of circuit".
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                    Comment

                    • leov
                      Member
                      • Mar 2011
                      • 45

                      #11
                      Re: HP lcd L1502 15"

                      Originally posted by retiredcaps
                      I usually test components "in circuit". If the readings are suspicious, then I desolder and measure "out of circuit".

                      Hi Retiredcaps,

                      I've read that you do that, but I don't know how to test it. I am going to read about it and try testing it right now.


                      Thanx for advice. I appreciate it.

                      Comment

                      • leov
                        Member
                        • Mar 2011
                        • 45

                        #12
                        Re: HP lcd L1502 15"

                        So here is the pic of the transistors i need to test. How do I go about testing them? I tried setting my meter to 200 ohms. When i connect positive lead to B and negative to E or C i get random readings that stabilize around 0.9-8. If I test from E to B and from C to E i just get random readings that do not stabilize. I am not sure if I am doing this right. Thank you for putting up with me. Any help would be appreciated.

                        leo
                        Attached Files

                        Comment

                        • PlainBill
                          Badcaps Legend
                          • Feb 2009
                          • 7034
                          • USA

                          #13
                          Re: HP lcd L1502 15"

                          Originally posted by leov
                          So here is the pic of the transistors i need to test. How do I go about testing them? I tried setting my meter to 200 ohms. When i connect positive lead to B and negative to E or C i get random readings that stabilize around 0.9-8. If I test from E to B and from C to E i just get random readings that do not stabilize. I am not sure if I am doing this right. Thank you for putting up with me. Any help would be appreciated.

                          leo
                          Are you testing with the monitor unplugged?

                          Please attach a picture of your meter with the function switch set in the position you are using, and with the probes plugged in..

                          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

                          • leov
                            Member
                            • Mar 2011
                            • 45

                            #14
                            Re: HP lcd L1502 15"

                            Originally posted by PlainBill
                            Are you testing with the monitor unplugged?

                            Please attach a picture of your meter with the function switch set in the position you are using, and with the probes plugged in..

                            PlainBill
                            monitor is not plugged in. I will attach the picture in a bit.

                            OK here are the pics of my meter:
                            Attached Files
                            Last edited by leov; 03-12-2011, 10:36 PM.

                            Comment

                            • PlainBill
                              Badcaps Legend
                              • Feb 2009
                              • 7034
                              • USA

                              #15
                              Re: HP lcd L1502 15"

                              Originally posted by leov
                              monitor is not plugged in. I will attach the picture in a bit.

                              OK here are the pics of my meter:
                              You definitely have the meter set to the correct range, and the leads plugged in correctly for resistance measurements. The display shows a typical display for a resistance greater than 200 ohms.

                              I can't explain the strange behavior. Ordinarily I would expect to see this display between any two legs of a transistor. A jitter of the last digit isn't unusual. What reading do you get when you try to measure the resistance between two points on the circuit board that are obviously connected, for example, the emitter of the two transistors in post 12?

                              PlainBill
                              Last edited by PlainBill; 03-13-2011, 07:04 AM.
                              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

                              • alexanna
                                Member
                                • Mar 2010
                                • 1346

                                #16
                                Re: HP lcd L1502 15"

                                Originally posted by leov
                                So here is the pic of the transistors i need to test. How do I go about testing them? I tried setting my meter to 200 ohms. When i connect positive lead to B and negative to E or C i get random readings that stabilize around 0.9-8. If I test from E to B and from C to E i just get random readings that do not stabilize. I am not sure if I am doing this right. Thank you for putting up with me. Any help would be appreciated.

                                leo
                                The readings your getting with your ohmmeter, the jumping and taking time to settle down makes me wonder if you may have a problem with your DMM leads?What reading do you get on the 200 ohm scale with the leads of your meter hooked together?
                                Don't forget to read PlainBill's above post.
                                Whatever I do, I consider it a success, if in the end I am breathing, seeing, feeling and hearing!

                                Comment

                                • leov
                                  Member
                                  • Mar 2011
                                  • 45

                                  #17
                                  Re: HP lcd L1502 15"

                                  Originally posted by alexanna
                                  The readings your getting with your ohmmeter, the jumping and taking time to settle down makes me wonder if you may have a problem with your DMM leads?What reading do you get on the 200 ohm scale with the leads of your meter hooked together?
                                  Don't forget to read PlainBill's above post.
                                  it reads 00.1, 00.3. The last digit is flirting between .4 and .1 and if i understand it correctly, Bill said that its ok if that happens. I am going to post a pic of the readings that I got when i tested another set of C5707 on the board.

                                  Comment

                                  • leov
                                    Member
                                    • Mar 2011
                                    • 45

                                    #18
                                    Re: HP lcd L1502 15"

                                    Originally posted by PlainBill
                                    You definitely have the meter set to the correct range, and the leads plugged in correctly for resistance measurements. The display shows a typical display for a resistance greater than 200 ohms.

                                    I can't explain the strange behavior. Ordinarily I would expect to see this display between any two legs of a transistor. A jitter of the last digit isn't unusual. What reading do you get when you try to measure the resistance between two points on the circuit board that are obviously connected, for example, the emitter of the two transistors in post 12?

                                    PlainBill
                                    Bill, here is what i did. I think that I found the bad transistors. Please see the picture. Th3 has pointed me to those before, but with everyone's help and a little of reading here on the forum i think i got it. Please confirm my findings.

                                    Thank you for your help guys.

                                    leo
                                    Attached Files

                                    Comment

                                    • steve2
                                      Senior Member
                                      • Dec 2010
                                      • 121

                                      #19
                                      Re: HP lcd L1502 15"

                                      When they read bad in circuit, you need to remove them from the board and recheck them. You may be reading transformers windings to get a reading that low or something else.

                                      Comment

                                      • PlainBill
                                        Badcaps Legend
                                        • Feb 2009
                                        • 7034
                                        • USA

                                        #20
                                        Re: HP lcd L1502 15"

                                        Originally posted by leov
                                        Bill, here is what i did. I think that I found the bad transistors. Please see the picture. Th3 has pointed me to those before, but with everyone's help and a little of reading here on the forum i think i got it. Please confirm my findings.

                                        Thank you for your help guys.

                                        leo
                                        You can verify the readings by removing them from the board, but they are almost certainly bad. This circuit is what is known as a Royer Oscillator. In it the two bases are tied together by a transformer winding and the two collectors are tied to the 12V supply through transformer windings. There should be no direct Collector-Emitter short.

                                        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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