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LCD 19" BENQ T905 problems

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    Re: LCD 19" BENQ T905 problems

    Hi to all,
    changed transistor and with 7 dollar monitor work ok...
    Thanks to all in this forum

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      Re: LCD 19" BENQ T905 problems

      Wanted to stop in and post and say that this helped me in repairing my monitor. Thanks to all who contributed, and contribute to other threads like this.

      cheers

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        Re: LCD 19" BENQ T905 problems

        Seems Im the only one who couldnt repair his TFT

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          Re: LCD 19" BENQ T905 problems

          Hello everyone, I too have a benq t905 which is not working. I opened it and I found a blown fuse so I thought the problem was easily solvable. However replacing the fuse was a no go. Lamps don't light up, I can see the faint "benq" logo when I turn on the monitor. I'm going to check capacitors tomorrow. Any advice would be useful, thanks.

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            Re: LCD 19" BENQ T905 problems

            Originally posted by chriz74 View Post
            Lamps don't light up, I can see the faint "benq" logo when I turn on the monitor.
            Post clear focused pictures of your boards using the manage attachments function. Please do not post pictures inline.

            Benq style power/inverter boards typically have more than one fuse. The main fuse by the AC plug and the picofuse.
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              Re: LCD 19" BENQ T905 problems

              Originally posted by retiredcaps View Post
              Post clear focused pictures of your boards using the manage attachments function. Please do not post pictures inline.

              Benq style power/inverter boards typically have more than one fuse. The main fuse by the AC plug and the picofuse.
              Is this clear enough? There's no sun light available at the moment.
              I tested the PF801 (is this the pico fuse?). Strange thing happens, the tester is stuck at 1 but some times it gives values then goes back to 1. Any clue?

              Last edited by chriz74; 05-03-2011, 03:13 PM.

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                Re: LCD 19" BENQ T905 problems

                Originally posted by chriz74 View Post
                Is this clear enough? There's no sun light available at the moment.
                I tested the PF801 (is this the pico fuse?). Strange thing happens, the tester is stuck at 1 but some times it gives values then goes back to 1. Any clue?
                (Sigh) Standard problem. The solder joints on the transformer pins crack. This results in one of the transistors staying on; it shorts, and blows the fuse.

                Replace the fuse without replacing the shorted transistors and it will blow again. Replace the transistors without resoldering the pins on the 4 inverter transformers and a transistor will short again.

                This inverter design is a Royer oscillator, it is used by Benq who supplies monitors to both Dell and HP. It MIGHT not have been discussed in this thread, now it is.

                However you are correct about one thing. This is an excellent opportunity to recap.

                And to repeat what retiredcaps said, don't post pictures inline. Use Manage Attachments below the test entry area.

                PlainBill
                Last edited by PlainBill; 05-03-2011, 06:34 PM.
                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.

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                  Re: LCD 19" BENQ T905 problems

                  I don't see any crack in the solder joints, the fuse I replaced didn't blow again. I did not replace the pf801 . Btw what are the specs for this PF?

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                    Re: LCD 19" BENQ T905 problems

                    Originally posted by chriz74 View Post
                    Btw what are the specs for this PF?
                    The picofuse for most Benq boards is 3A 125V.

                    We KNOW this board very well. If you don't resolder as PlainBill states, you will have problems in the future. If you look at all the Benq board posts, it is the same advice over and over.
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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.

                    Please do not post inline and offsite as they slow down the loading of pages.

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                      Re: LCD 19" BENQ T905 problems

                      Originally posted by retiredcaps View Post
                      The picofuse for most Benq boards is 3A 125V.

                      We KNOW this board very well. If you don't resolder as PlainBill states, you will have problems in the future. If you look at all the Benq board posts, it is the same advice over and over.
                      125V, are you positive? Cause the main fuse is 2A 250v.

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                        Re: LCD 19" BENQ T905 problems

                        Originally posted by chriz74 View Post
                        125V, are you positive? Cause the main fuse is 2A 250v.
                        The main fuse is rated for 250 volts because the monitor may be plugged into circuits carrying up to 230 volts. The picofuse is rated at 125 volts because it is in a circuit carrying only 12 volts.

                        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


                          Re: LCD 19" BENQ T905 problems

                          update. I found two "2sc5707" are faulty and also the "1200AP40 CPBY 05475".
                          I tried to test the lamps and i get no value, is this normal?
                          Last edited by chriz74; 05-04-2011, 09:26 AM.

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                            Re: LCD 19" BENQ T905 problems

                            Originally posted by chriz74 View Post
                            update. I found two "2sc5707" are faulty and also the "1200AP40 CPBY 05475".
                            I tried to test the lamps and i get no value, is this normal?
                            How did you try to test the lamps? A CCFL requires about 600-1000 volts to ignite. Unless you used a tester that produces that kind of voltage, you wouldn't get any results.

                            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.

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                              Re: LCD 19" BENQ T905 problems

                              It was really a relative of mine so I don't know what kind of tester he used. I'll ask. What about the 1200AP40 BLOWN, how does that sound to you? Is this normal fault? As a result there was no power being spread to the lamp connectors.

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                                Re: LCD 19" BENQ T905 problems

                                Originally posted by chriz74 View Post
                                What about the 1200AP40 BLOWN, how does that sound to you?
                                How did you determine that this is blown???
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                                  Re: LCD 19" BENQ T905 problems

                                  Because it doesnt read 12v but 300v

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                                    Re: LCD 19" BENQ T905 problems

                                    Originally posted by chriz74 View Post
                                    update. I found two "2sc5707" are faulty and also the "1200AP40 CPBY 05475".
                                    I tried to test the lamps and i get no value, is this normal?
                                    The lamps are likely not a problem.
                                    Can't speak for the 1200AP40, as you didn't really tell us what you measured, and how you determined.

                                    As many have tried to tell you, this monitor has a very common failure mode.
                                    Bad solder joints on the inverter transformers cause transistors to short, and blow pico fuses. Check ALL the 5707s, and the FETs, replace any bad ones, replace the fuse, while you're in there, recap, and then fire it up.

                                    Of the 22 or so monitors I've repaired in the last year or so (and I'm still a newbie learning) several were this model or similar, and had this common failure.
                                    36 Monitors, 3 TVs, 4 Laptops, 1 motherboard, 1 Printer, 1 iMac, 2 hard drive docks and one IP Phone repaired so far....

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                                      Re: LCD 19" BENQ T905 problems

                                      Originally posted by retiredcaps View Post
                                      How did you determine that this is blown???
                                      The only part corresponding to 1200AP40 is a SMPS controller. If you can still see the Benq logo as you mentioned in post 7 the 1200AP40 is good.

                                      Really, this is a waste of time in my opinion. It's difficult enough assisting in troubleshooting a monitor if the person doing the real work is interacting with us. If there is an intermediate party (you), communication becomes impossible.

                                      1. Check for 5V and 12V from the power supply. If they are present:

                                      2. Remove as much solder as possible from the transformer pins and resolder with real solder, not this lead free junk Benq inflicted on everyone.

                                      3. Replace both 2SC5707s in a pair if either are shorted

                                      4. Check both FU9024N, replace any that are associated with a shorted 2sc5707

                                      5. Replace the picofuse if it is open.

                                      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


                                        Re: LCD 19" BENQ T905 problems

                                        Thanks for the advices, I'll tell what turns out. BTW I can't see the BENQ logo anymore so I suppose the 1200AP40 is really gone. Oh I got the schematics from BENQ, I think it could be useful for future reference.

                                        Attached Files
                                        Last edited by chriz74; 05-05-2011, 02:08 AM.

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                                          Re: LCD 19" BENQ T905 problems

                                          Originally posted by chriz74 View Post
                                          BTW I can't see the BENQ logo anymore so I suppose the 1200AP40 is really gone.
                                          If the power LED is green or yellow, the power supply and logic card are likely to be working. That is, 1200AP40 is working.
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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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