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    #1

    HP1940 backlight

    I have an HP1940 19" LCD monitor, and the backlight isn't working. I'm not sure if it's the bulb or driver. Is there a safe way to test? I have a multimeter and know how to use it. If the parts are inexpensive enough, I might repair it.
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    #2
    Re: HP1940 backlight

    You'll have to pull off the cover and post some clear focused photos of the power board using the "manage attachments" button.

    Comment

      #3
      Re: HP1940 backlight

      OK I'll do that when I get a chance. Can you tell if the bulb is burned out by looking at it or testing continuity/impedance/voltage across it?

      Comment

        #4
        Re: HP1940 backlight

        If this is a Benq style board, it is likely one or more of the following.

        1) inverter transformer pins MUST be resoldered
        2) picofuse could be blown (open)
        3) c5707 transistors are shorted
        4) fu9024 fets are shorted

        Take it apart and post pictures using the manage attachments functions and do not post inline or offsite.
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        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.

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          #5
          Re: HP1940 backlight

          Originally posted by timelessbeing View Post
          OK I'll do that when I get a chance. Can you tell if the bulb is burned out by looking at it or testing continuity/impedance/voltage across it?
          You MAY be able to tell if you strip them out,but that happens, only if you have confirmed one or more is causing the problem, either because the lamp has failed ot the wiring has burnt out,normally on one of the return wires.
          Your multimeter is of no use to test these, and you really need a test ccfl to determine if they are causing the fault.

          Comment

            #6
            Re: HP1940 backlight

            Hey guys. I found what appear to be scorched transistors on the BenQ power supply board. (see attachments). Does anybody know how much these cost, and a good supplier? (preferably in Canada).
            Attached Files

            Comment

              #7
              Re: HP1940 backlight

              Originally posted by timelessbeing View Post
              Does anybody know how much these cost, and a good supplier? (preferably in Canada).
              Good luck finding parts in Canada. I ordered mine off ebay.ca. Just search for c5707 kit. It should be around $4 to $6 and you will likely get

              4 - c5707s
              2 - fu9024s
              1 - 3A 125V picofuse

              edit: The damage looks pretty bad. It might be beyond repair, but the cost is relatively low and it is worth trying to save a 19 inch monitor?
              Last edited by retiredcaps; 05-09-2011, 05:24 PM.
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              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

                #8
                Re: HP1940 backlight

                You probably won't find these in Canada, and if you do, they'll be marked up 800%
                Ebay is your best bet.
                Test the ones that aren't charred, they could be bad too.
                36 Monitors, 3 TVs, 4 Laptops, 1 motherboard, 1 Printer, 1 iMac, 2 hard drive docks and one IP Phone repaired so far....

                Comment

                  #9
                  Re: HP1940 backlight

                  On closer inspection with a bright light the damaged components are:
                  C5707 (x2)
                  D10PF (attached)

                  I found this repair kit on eBay for $5:
                  http://cgi.ebay.com/ws/eBayISAPI.dll...m=220778537253
                  (USA is much better than waiting a month for it to come from China!)
                  The board in the ad doesn't look like mine. Also, they provide a FU9024N and a 3A fuse. Mine is 5A (see attached). Is it the right kit?

                  Can any of these components be damaged by a soldering iron? What are the test values for the transistors?
                  Attached Files

                  Comment

                    #10
                    Re: HP1940 backlight

                    The FU9024N will work in place of the D10PF, I've done it, and lived to tell about it.
                    If you don't know how to test, or don't have the equipment, it might be just as easy to replace them all, they're cheap enough.

                    USA might be just as slow as China, lately shipments via Canada Post have been very slow, but it does vary, so you might get lucky.

                    The 5A fuse might explain the crispyness of the transistors. Hard to say what the original should have been, 5 seems high, but might be original. On the BenQ models I've done that have a similar circuit, it's always been a 3A.

                    You generally won't damage them with soldering heat during install, if you're any good at soldering. De-soldering them if you're not good, could damage, but they're already toasty anyway.
                    Last edited by smason; 05-09-2011, 06:18 PM.
                    36 Monitors, 3 TVs, 4 Laptops, 1 motherboard, 1 Printer, 1 iMac, 2 hard drive docks and one IP Phone repaired so far....

                    Comment

                      #11
                      Re: HP1940 backlight

                      Originally posted by timelessbeing View Post
                      Mine is 5A (see attached).
                      You can easily test to see if the existing fuse is good or not. A good fuse should measure less than 1.0 ohms.
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                        #12
                        Re: HP1940 backlight

                        Originally posted by smason View Post
                        The 5A fuse might explain the crispyness of the transistors. Hard to say what the original should have been, 5 seems high, but might be original. On the BenQ models I've done that have a similar circuit, it's always been a 3A.
                        This fuse definitely came with the monitor, so I hope it still works. I think model 1940 (part no. PF803) is uncommon. You usually see the L1940 (PF803AA) or L1940T (EM869AA).

                        Comment

                          #13
                          Re: HP1940 backlight

                          This company will sell you the entire board if you want to pay a little extra.
                          http://www.lcdrepair.us/Invpowersupply.html

                          Comment

                            #14
                            Re: HP1940 backlight

                            Nah, we don't buy boards here, we fix 'em!

                            That said, their prices look pretty reasonable.
                            I'm waiting to find a replacement transformer for a Dell monitor on my shelf. They'll sell the whole inverter for $20.00 Tempting, but I don't like the monitor *that* much, plus with shipping to Canada, it definitely won't be worth it.

                            I know I'll eventually find a donor monitor.
                            36 Monitors, 3 TVs, 4 Laptops, 1 motherboard, 1 Printer, 1 iMac, 2 hard drive docks and one IP Phone repaired so far....

                            Comment

                              #15
                              Re: HP1940 backlight

                              Just wind your own transformer! hehe J/K. There's monitors all over craigslist. You might even be able to pull a step-up xformer out of some other appliance.

                              By the way, check out this youtube channel and watch a crazy brit pump kV's and kA's into various devices and objects :P The coconuts are the most entertaining.
                              http://www.youtube.com/user/Photonicinduction

                              Comment

                                #16
                                Re: HP1940 backlight

                                Brit, with a capital B please.......

                                Comment

                                  #17
                                  Re: HP1940 backlight

                                  Originally posted by Rtech View Post
                                  Brit, with a capital B please.......
                                  Oh bloody 'ell.
                                  36 Monitors, 3 TVs, 4 Laptops, 1 motherboard, 1 Printer, 1 iMac, 2 hard drive docks and one IP Phone repaired so far....

                                  Comment

                                    #18
                                    Re: HP1940 backlight

                                    Blimey!

                                    I got my eBay repair kit today (shipped out May 5th) nicely packaged in a static shielded baggy. (Seller was "coreweave" for those wondering). I marked the connectors so I don't mix them up. I'll begin the repair when I get home from work tonight.

                                    I have a couple of questions for you guys. Some of the traces have lifted away from the PCB. My plan is to just reflow the solder, leave as is, test the monitor, and if needed, add some wire segments and clean away excess rosin with isopropyl alcohol since they could be high-voltage circuits. What would you do?

                                    The transformers look OK, but I should resolder them right? All four?

                                    Thanks.
                                    - Joe
                                    Attached Files

                                    Comment

                                      #19
                                      Re: HP1940 backlight

                                      Originally posted by timelessbeing View Post
                                      The transformers look OK, but I should resolder them right? All four?
                                      You *MUST* resolder all the 4 inverter transformers. These Benq style boards have poor soldering on the inverter transformers which causes the picofuse to blow and other problems.
                                      --- 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

                                        #20
                                        Re: HP1940 backlight

                                        Originally posted by retiredcaps View Post
                                        You *MUST* resolder all the 4 inverter transformers. These Benq style boards have poor soldering on the inverter transformers which causes the picofuse to blow and other problems.
                                        OK, will do. Please pardon my ignorance, but how does the fuse blow anyway? Don't bad solder joints increase impedance and restrict current?

                                        Comment

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