Another bad HP 1955 Inverter... probably

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  • ofcsilencer
    New Member
    • Jan 2009
    • 7

    #1

    Another bad HP 1955 Inverter... probably

    I have been watching the forums for some time now and I have been able to fix a few screens with the guidance I picked up here.

    The screen I am having problems with is a benq 48.l1a02.a41, I think it's a version 94v-0. I saw several people had articles about this screen and how to fix it.

    The problem I am having is the screens backlight kicks off after a second or two right after powering on.

    I looked at the capacitors and they are brands that I remember people complaining about (elite for example). None of the caps seem bubbled but I guess that isn't really required.

    I also heard people talking about the ccfl bulbs actually being bad or shorted, don't know if this would help but I tried running them one at a time to see if I got better results and no.

    Would a capacitance meter help check these? If so I'll buy one since ill probably use it more often.

    Strange thing I noticed with the 5707 transistors? I test them with a meter and I get one resistance reading and then the meter zeroes out. Is that normal?

    Im not an electronics genius but I do have a basic knowledge of the parts and have taken a class on electronics. Spent a few months repairing overheads and other SIMPLE electronics but that's poor experience.

    Any ideas?
  • Krankshaft
    Badcaps Legend
    • Jan 2007
    • 2328
    • USA

    #2
    Re: Another bad HP 1955 Inverter... probably

    It definitely sounds like a shorted C5707 to me.

    You should be using the diode check function and not the resistance function on the meter.

    From base to collector and reverse the probes you should only get a voltage drop in one direction. The same from base to emitter.

    They can be measured in circuit (to determine which pair has a bad transistor) once you've found out which pair is bad. Remove and replace both transistors even if the other one is fine.
    Last edited by Krankshaft; 01-08-2009, 09:22 AM.
    Elements of the past and the future combining to make something not quite as good as either.

    Comment

    • ofcsilencer
      New Member
      • Jan 2009
      • 7

      #3
      Re: Another bad HP 1955 Inverter... probably

      ok i replaced all 4 just to be sure, meter i have didn't allow me to test them in circuit. but its still doing the same thing.

      it will power up the display for a few seconds then when the dialog switches to check vga cable it then doesn't light but yet the light is green.

      not sure where i should look next

      Comment

      • Toasty
        Badcaps Legend
        • Jul 2007
        • 4171

        #4
        Re: Another bad HP 1955 Inverter... probably

        I am not familiar with this particular board, but it sounds like it's tripping the over current protection.
        veritas odium parit

        Comment

        • PlainBill
          Badcaps Legend
          • Feb 2009
          • 7034
          • USA

          #5
          Re: Another bad HP 1955 Inverter... probably

          Originally posted by ofcsilencer
          ok i replaced all 4 just to be sure, meter i have didn't allow me to test them in circuit. but its still doing the same thing.

          it will power up the display for a few seconds then when the dialog switches to check vga cable it then doesn't light but yet the light is green.

          not sure where i should look next
          This is the typical symptom of the backlight inverter detecting a fault condition and shutting down. The problem is determining the nature of the fault and correcting it. As far as I know, it could be a CCFL drawing too much current - or too little current. It could be a bad cap, it could even be a resistor or cap that is out of tolerance.

          I've got one with the same problem. I'm taking the approach of first replacing all questionable caps (the present caps were described as 'garbage'). That will cost less than $5 for the parts, and is a heck of a lot easier than replacing the CCFLs. After that - well, we'll see.

          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

          • EGuevarae
            Badcaps Legend
            • Nov 2008
            • 1336
            • USA

            #6
            Re: Another bad HP 1955 Inverter... probably

            Originally posted by ofcsilencer
            I have been watching the forums for some time now and I have been able to fix a few screens with the guidance I picked up here.

            The screen I am having problems with is a benq 48.l1a02.a41, I think it's a version 94v-0. I saw several people had articles about this screen and how to fix it.

            The problem I am having is the screens backlight kicks off after a second or two right after powering on.

            I looked at the capacitors and they are brands that I remember people complaining about (elite for example). None of the caps seem bubbled but I guess that isn't really required.

            I also heard people talking about the ccfl bulbs actually being bad or shorted, don't know if this would help but I tried running them one at a time to see if I got better results and no.

            Would a capacitance meter help check these? If so I'll buy one since ill probably use it more often.

            Strange thing I noticed with the 5707 transistors? I test them with a meter and I get one resistance reading and then the meter zeroes out. Is that normal?

            Im not an electronics genius but I do have a basic knowledge of the parts and have taken a class on electronics. Spent a few months repairing overheads and other SIMPLE electronics but that's poor experience.

            Any ideas?
            Welcome to the forums

            You say you've repaired some units so far. Can you get another LCD Panel/set of lamps to test with this inverter? That would rule out the CCFLs being bad.

            Did you notice any red/orange/pink hue when they start up?
            Also, did you check the removed transistors to see if they have failed?
            One last thing. Even if the four lamps are OK, if you only connect one (or connect three or just two), the inverter would detect that as a fault and will shut down itself.
            Last edited by EGuevarae; 03-11-2009, 06:27 PM.
            There are 10 kind of people in this world: those that understand binary, and those who don't.
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            Comment

            • FIXITNOW
              Senior Member
              • Jun 2008
              • 128
              • UK

              #7
              Re: Another bad HP 1955 Inverter... probably

              these is a small fuse that blows when you have a shorted c5707 you will need to replace it

              Comment

              • ofcsilencer
                New Member
                • Jan 2009
                • 7

                #8
                Re: Another bad HP 1955 Inverter... probably

                i did try testing one lamp at a time, and i did get the result mentioned above, but each bulb did light, i was curious to see if all 4 would light and they did but then it would shutoff.

                i do have another screen that a botched the replacement of some c5707s and destroyed a trace (handy i ordered alot of c5707s) so i might be able to use the bulbs from it. it is also a benq board.

                i tried testing the c5707's , due to my poor abilit ywith a soldering iron i ripped the pin out of 2 of them, but the ones i was able to test all measured like 292 or something on the diode reading. not quite sure what that means.

                i was looking at replacing the capacitors, but where would you recommend ordering them. i keep looking at mcmelectronics (out of habbit), and i read somewhere i should use esr caps.

                also what is this fuse i should be looking for?

                Comment

                • Bobdee
                  Badcaps Veteran
                  • Jun 2008
                  • 461

                  #9
                  Re: Another bad HP 1955 Inverter... probably

                  Hello
                  The fuse you are after is on the right side of the big transformer in the picture of this link, its black and resembles a diode

                  https://www.badcaps.net/forum/showpo...58&postcount=3

                  the fuse number is PF703 on the board, the fuse in the picture is not the correct Amp, so go by what your Amp is

                  Comment

                  • PlainBill
                    Badcaps Legend
                    • Feb 2009
                    • 7034
                    • USA

                    #10
                    Re: Another bad HP 1955 Inverter... probably

                    The caps can be ordered from either Mouser or Digi-Key. Neither company has a minimum order, but I prefer Digi-Key. Their minimum shipping charge is less than $2.50; Mouser charges nearly $7.00. This makes quite a difference on a small order.

                    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

                    • EGuevarae
                      Badcaps Legend
                      • Nov 2008
                      • 1336
                      • USA

                      #11
                      Re: Another bad HP 1955 Inverter... probably

                      Originally posted by Bobdee
                      Hello
                      The fuse you are after is on the right side of the big transformer in the picture of this link, its black and resembles a diode

                      https://www.badcaps.net/forum/showpo...58&postcount=3

                      the fuse number is PF703 on the board, the fuse in the picture is not the correct Amp, so go by what your Amp is
                      Good one Bob. I didn't see it in the picture until you told where it was located. That would be the one with the problem if the lamps were dead, but he says that they lit and then shut off, and when I've ran into open fuses on inverter area, the lamps didn't lit at all. Anyone here has worked with this specific board before?
                      There are 10 kind of people in this world: those that understand binary, and those who don't.
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                      Comment

                      • Bobdee
                        Badcaps Veteran
                        • Jun 2008
                        • 461

                        #12
                        Re: Another bad HP 1955 Inverter... probably

                        Originally posted by eguevarae
                        . Anyone here has worked with this specific board before?
                        I have done a couple ,problems is always 2sc5707 + the fuse, and a lot of resoldering all over board, in particular components on h/sinks, but more so the 4 inverter transformers, is a must for resoldering ,loads of ring cracks, check the whole board for bad solder.

                        edit look at that picture in that link i gave earlier the board is brown by transformer and the 2sc5707 are pulled , usual problem
                        Last edited by Bobdee; 03-12-2009, 03:38 PM.

                        Comment

                        • ofcsilencer
                          New Member
                          • Jan 2009
                          • 7

                          #13
                          Re: Another bad HP 1955 Inverter... probably

                          ill give it a shot retouching the solder on the HV transformers. probably order the caps and fuse this weekend if that doesn't work.

                          thanks!

                          Comment

                          • EGuevarae
                            Badcaps Legend
                            • Nov 2008
                            • 1336
                            • USA

                            #14
                            Re: Another bad HP 1955 Inverter... probably

                            Originally posted by Bobdee
                            I have done a couple ,problems is always 2sc5707 + the fuse, and a lot of resoldering all over board, in particular components on h/sinks, but more so the 4 inverter transformers, is a must for resoldering ,loads of ring cracks, check the whole board for bad solder.

                            edit look at that picture in that link i gave earlier the board is brown by transformer and the 2sc5707 are pulled , usual problem
                            You're right. Now that you mention it, it makes sense. Thanks for the info, Bob.
                            There are 10 kind of people in this world: those that understand binary, and those who don't.
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                            Comment

                            • HOODLAM
                              Member
                              • Dec 2007
                              • 20

                              #15
                              Re: Another bad HP 1955 Inverter... probably

                              Hi Guys.

                              I also have an HP1955 which gave problems, replaced the rf9024n transistors(high ferq switch) x4. Screen been running for over a year now with now problems.if you search for previous thread on bad caps where I spoke to Kranshaft and Davmax regarding the repairs and checks. It sounds to me as if could be the 9024n's which are "breaking down" on the starting current!
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                              Comment

                              • SimonNZ
                                New Member
                                • Apr 2009
                                • 3

                                #16
                                Re: Another bad HP 1955 Inverter... probably

                                I have just recieved a dead HP 1955 monitor that once opened shows a spectacularly blown up c5707. Seems like a very common theme!

                                Comment

                                • Bobdee
                                  Badcaps Veteran
                                  • Jun 2008
                                  • 461

                                  #17
                                  Re: Another bad HP 1955 Inverter... probably

                                  Originally posted by SimonNZ
                                  I have just recieved a dead HP 1955 monitor that once opened shows a spectacularly blown up c5707. Seems like a very common theme!
                                  Hello Simon
                                  You may have a bigger problem here by what you say above,
                                  2SC5707,s do not show any visual signs of damage even when shorted, when you examine them in my experiences, and I have never found a thread that had posted on that either.
                                  Best get some help, post Pictures of top and bottom of board, a lot of the lads would like to see this, and they will help you out as well.
                                  bob
                                  Last edited by Bobdee; 04-02-2009, 03:50 AM.

                                  Comment

                                  • EGuevarae
                                    Badcaps Legend
                                    • Nov 2008
                                    • 1336
                                    • USA

                                    #18
                                    Re: Another bad HP 1955 Inverter... probably

                                    Originally posted by Bobdee
                                    Hello Simon
                                    You may have a bigger problem here by what you say above,
                                    2SC5707,s do not show any visual signs of damage even when shorted, when you examine them in my experiences, and I have never found a thread that had posted on that either.
                                    Best get some help, post Pictures of top and bottom of board, a lot of the lads would like to see this, and they will help you out as well.
                                    bob
                                    Never seen one "exploded" myself, so the cause might be something around it. Pics would help as Bob said.
                                    There are 10 kind of people in this world: those that understand binary, and those who don't.
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                                    • SimonNZ
                                      New Member
                                      • Apr 2009
                                      • 3

                                      #19
                                      Re: Another bad HP 1955 Inverter... probably

                                      All right, bugger! Well here is the full carnage from this component letting out it's smoke. Any ideas? So you think if I replace it the same thing will happen again?
                                      Attached Files

                                      Comment

                                      • SimonNZ
                                        New Member
                                        • Apr 2009
                                        • 3

                                        #20
                                        Re: Another bad HP 1955 Inverter... probably

                                        Just noticed - how do you like the misspelled Hight Voltage right next to it haha

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