benq fp731 backlight problem

Collapse
X
 
  • Time
  • Show
Clear All
new posts
  • haku
    New Member
    • May 2008
    • 3

    #1

    benq fp731 backlight problem

    hi, i'm new here, but did a bit of searching and found many others with the same problem I have.

    The backlight on the monitor seems to be busted ( I can see a faint image if I shine a flashlight to it).


    So everyone seemed to narrow it down to either the 4 (Q740/Q739/Q759/Q760) 2SC5707 transistors or the pf751 fuse 3amp.

    When I was taking the board out, I accidently ripped out a leg on the item circled in red, it's labelled "L603", can anyone tell me where I can source (or the name of it) another part out??


    I'm familiar with soldering (audio cables), but not PCB soldering. So what reading am I looking for when I test the transistors/fuse of the board to see if it's fried or not? And since there are 3 legs/pins on the transistor, which is which


    thanks for your time



    PS: these transistors will work 'just as well' as the originals? http://cgi.ebay.com/MJE3055T-MJE3055...2em118Q2el1247
    Attached Files
  • Spacedye69
    Badcaps Veteran
    • Nov 2005
    • 698
    • US

    #2
    Re: benq fp731 backlight problem

    I just bought some 2sc5707 from this guy. On the transistors, your more than likely looking for a short between 2 of the legs. The legs are labeled E C B on the board. The fuse just check for continuity.

    I cant see any red circle.

    Comment

    • haku
      New Member
      • May 2008
      • 3

      #3
      Re: benq fp731 backlight problem

      hi oops, i reuploaded the pic


      i found that ebay seller too unfortunately they want 7$ to ship to canada


      thanks


      ps: is it just me or can you not edit a first post?
      Attached Files

      Comment

      • MikeM
        New Member
        • May 2008
        • 5

        #4
        Re: benq fp731 backlight problem

        You can get 2sc5707 in Australia for A$1.75 ea. Won't be far different in value in C$'s. L303 just seems to be a wire wound thru 3 times and exiting as 2 leads. Should be easy fix unless you have damaged the ferrite 'casing'.

        Comment

        • c_hegge
          Badcaps Legend
          • Sep 2009
          • 5219
          • Australia

          #5
          Re: benq fp731 backlight problem

          I have the same problem with the same monitor. I'll try replacing these parts and post back with results.
          I love putting bad caps and flat batteries in fire and watching them explode!!

          No wonder it doesn't work! You installed the jumper wires backwards

          Main PC: Core i7 3770K 3.5GHz, Gigabyte GA-Z77M-D3H-MVP, 8GB Kingston HyperX DDR3 1600, 240GB Intel 335 Series SSD, 750GB WD HDD, Sony Optiarc DVD RW, Palit nVidia GTX660 Ti, CoolerMaster N200 Case, Delta DPS-600MB 600W PSU, Hauppauge TV Tuner, Windows 7 Home Premium

          Office PC: HP ProLiant ML150 G3, 2x Xeon E5335 2GHz, 4GB DDR2 RAM, 120GB Intel 530 SSD, 2x 250GB HDD, 2x 450GB 15K SAS HDD in RAID 1, 1x 2TB HDD, nVidia 8400GS, Delta DPS-650BB 650W PSU, Windows 7 Pro

          Comment

          • c_hegge
            Badcaps Legend
            • Sep 2009
            • 5219
            • Australia

            #6
            Re: benq fp731 backlight problem

            One other question before I order parts. would this be a suitable fuse?

            http://australia.rs-online.com/web/s...t&R=2509674449
            I love putting bad caps and flat batteries in fire and watching them explode!!

            No wonder it doesn't work! You installed the jumper wires backwards

            Main PC: Core i7 3770K 3.5GHz, Gigabyte GA-Z77M-D3H-MVP, 8GB Kingston HyperX DDR3 1600, 240GB Intel 335 Series SSD, 750GB WD HDD, Sony Optiarc DVD RW, Palit nVidia GTX660 Ti, CoolerMaster N200 Case, Delta DPS-600MB 600W PSU, Hauppauge TV Tuner, Windows 7 Home Premium

            Office PC: HP ProLiant ML150 G3, 2x Xeon E5335 2GHz, 4GB DDR2 RAM, 120GB Intel 530 SSD, 2x 250GB HDD, 2x 450GB 15K SAS HDD in RAID 1, 1x 2TB HDD, nVidia 8400GS, Delta DPS-650BB 650W PSU, Windows 7 Pro

            Comment

            • George Ortiz
              Senior Member
              • Oct 2009
              • 51

              #7
              Re: benq fp731 backlight problem

              I think the power supply in your Benq is that same power supply that's in my
              (free) Dell E173FPb. I troubleshot and found two shorted transisters. I ordered mine transistros off of ebay. Should have them here tommorrow. Spent $5.98 to get the 4 transistors, 2 other semiconductors and the small fuse. I was getting the power light only flashing when turning on the monitor

              Comment

              • c_hegge
                Badcaps Legend
                • Sep 2009
                • 5219
                • Australia

                #8
                Re: benq fp731 backlight problem

                Fixed it.

                I replaced the four 2SC5707 transistors and PF751 and it works now. I am amazed since the mounting of the transistors was entirely emprovised. I ordered them from RS Components and they arrived with the middle leg very short (like on a VRM MOSFET), so I used wires to connect to the pins on two of them and was able to mount the other two on the underside of the PCB. I also damaged a couple of the pads, so I joined the wires to the other parts in the circuit.

                I also replaced all the caps, except for the primary, with Panny FC
                I love putting bad caps and flat batteries in fire and watching them explode!!

                No wonder it doesn't work! You installed the jumper wires backwards

                Main PC: Core i7 3770K 3.5GHz, Gigabyte GA-Z77M-D3H-MVP, 8GB Kingston HyperX DDR3 1600, 240GB Intel 335 Series SSD, 750GB WD HDD, Sony Optiarc DVD RW, Palit nVidia GTX660 Ti, CoolerMaster N200 Case, Delta DPS-600MB 600W PSU, Hauppauge TV Tuner, Windows 7 Home Premium

                Office PC: HP ProLiant ML150 G3, 2x Xeon E5335 2GHz, 4GB DDR2 RAM, 120GB Intel 530 SSD, 2x 250GB HDD, 2x 450GB 15K SAS HDD in RAID 1, 1x 2TB HDD, nVidia 8400GS, Delta DPS-650BB 650W PSU, Windows 7 Pro

                Comment

                • smason
                  Badcaps Legend
                  • Feb 2010
                  • 1652
                  • Canada

                  #9
                  Re: benq fp731 backlight problem

                  Originally posted by haku
                  hi oops, i reuploaded the pic


                  i found that ebay seller too unfortunately they want 7$ to ship to canada


                  thanks


                  ps: is it just me or can you not edit a first post?
                  Where in Canada are you?
                  36 Monitors, 3 TVs, 4 Laptops, 1 motherboard, 1 Printer, 1 iMac, 2 hard drive docks and one IP Phone repaired so far....

                  Comment

                  • charliea
                    New Member
                    • Jul 2010
                    • 1

                    #10
                    Re: benq fp731 backlight problem

                    Originally posted by c_hegge
                    Fixed it.

                    I replaced the four 2SC5707 transistors and PF751 and it works now. I am amazed since the mounting of the transistors was entirely emprovised. I ordered them from RS Components and they arrived with the middle leg very short (like on a VRM MOSFET), so I used wires to connect to the pins on two of them and was able to mount the other two on the underside of the PCB. I also damaged a couple of the pads, so I joined the wires to the other parts in the circuit.

                    I also replaced all the caps, except for the primary, with Panny FC
                    Bought the kit but haven't put it in yet. Noticed one of the 470uf caps is bulging on top so I ordered 5 to replace all plus the 3 other 1000uf caps.

                    Ran a continuity test on the fuse and it was .5 ohms on my cheapie old needle type multimeter.

                    Since only the capacitor showed visible signs of a problem I was going to replace them first before replacing the transistors and fuse.

                    Sound like the right approach??

                    Comment

                    • retiredcaps
                      Badcaps Legend
                      • Apr 2010
                      • 9271

                      #11
                      Re: benq fp731 backlight problem

                      Originally posted by charliea
                      Ran a continuity test on the fuse and it was .5 ohms on my cheapie old needle type multimeter.

                      Since only the capacitor showed visible signs of a problem I was going to replace them first before replacing the transistors and fuse.

                      Sound like the right approach??
                      The fuse is good.

                      You can test the transistor for shorts using your analog multimeter. Just set it to ohms and test 1-2, 1-3, 2-3 on c5707. If it reads fine and the fuse reads fine, replace the caps and try the monitor.

                      On this board you may also find a FU9024. Check these for shorts too.

                      PS. Make sure to resolder ALL the transformer pins before turning on the monitor. They have reputation for being bad due to cold/dry/bad solder joints.
                      --- 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

                      Related Topics

                      Collapse

                      • Dobrowol
                        Asus GA402RK keyboard and kb backlight problem
                        by Dobrowol
                        Hi. I have a problem with Asus ROG GA402RK. The keyboard suddenly stopped working along with the kb backlight. I replaced the keyboard and the ITE KBC chip and the problem is still the same. I don't see any passive elements that look damaged. Does anyone have an idea?
                        04-28-2025, 04:30 PM
                      • ononos
                        LG M2362DP Backlight problem
                        by ononos
                        hello everyone!
                        As the title states i am an owner of an LG flatron M2362DP 23 inch monitor Tv. Since i currently use it as a tv i'm posting the problem on the "troubleshooting tvs and video sources" section.
                        I'm from Greece so English isn't my native language, so please forgive me for any mistakes i make. I have basic knowledge in electronics, and although i have a degree, many things have changed since i finished a 2 year coarse (over 30 years ago). Occasionally i repair easy stuff, mostly things that break at home like appliances.

                        So i decided to try to...
                        03-12-2023, 05:05 AM
                      • fanaticgames
                        Samsung UE32D4010 Backlight problem, led ok
                        by fanaticgames
                        hello I have a backlight problem on this TV, if I unplug the cn201 cable the backlight works perfectly and the voltages are 13v if I connect the cn201 cable the backlight goes off and the voltage drops to 12v, I assume it's a motherboard problem, the question is has anyone had a similar problem? I want to understand if the motherboard is repairable or it's not worth wasting time...
                        02-22-2023, 09:46 AM
                      • Honziq
                        Backlight problem - Asus M3200WU, board Gapal LA-L291p
                        by Honziq
                        Hello,

                        I have this All-in-one PC, after SSD change there is no picture. I was found out it is a backlight problem, but LEDs are OK. There is 4 led strings each working on 42,4V, but from board is comming only 5V.

                        I was repaired many backlights before but this design i will not understand.

                        For me it looks like it is waiting for some signal from screen to start up the backlight or something like this. Nothing seems to be damaged or shorted here.

                        Can someone explain me please what to do, what to check?

                        Thanks....
                        11-20-2024, 01:24 PM
                      • grbo92
                        Backlight problem Acer LA-031P
                        by grbo92
                        Hi,

                        i have one acer Nitro 5 without backlight on my desk.

                        Mainboard model: LA-L031P GH53Z REV 1B

                        Attached schematics and boardview are REV 1A, slightly different as REV 1B.

                        11411_LA-L031P-Acer_Nitro_5_AN515-45_AN517-41-GH53Z_Rev_ (1).zip

                        Repair history: customer cleaned dust and changed thermal paste, shortly after that there was no light

                        Notebook boots without problem and shows only image without backlight, HDMI output working. Optical inspection done, no burned or broken components. Tested also with a new display module....
                        09-09-2024, 03:49 AM
                      • Loading...
                      • No more items.
                      Working...