LCD 19" BENQ T905 problems

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  • retiredcaps
    replied
    Re: LCD 19" BENQ T905 problems

    Originally posted by capullaco
    Ok,the pico shows "1.", the normal one shows "0,2" so seems this one is ok.
    Your picofuse, as we suspected, is open or BAD. You will need to replace it.

    The transistor that burnt the board also seems ok, almost everytime showed a range out of range (showing "1.") and a few times showed a high value ,like 197 for a second then went out of range.
    The showing of 197 is your multimeter not reacting fast enough. For your own fun and learning, try testing the same transistor on the 2k, 20k, and 200k scale and see what you get.

    Leave a comment:


  • capullaco
    replied
    Re: LCD 19" BENQ T905 problems

    Ok,the pico shows "1.", the normal one shows "0,2" so seems this one is ok.

    The transistor that burnt the board also seems ok, almost everytime showed a range out of range (showing "1.") and a few times showed a high value ,like 197 for a second then went out of range.

    Leave a comment:


  • retiredcaps
    replied
    Re: LCD 19" BENQ T905 problems

    Originally posted by capullaco
    But one question, which ohm switch should I use? I got : 200,2k,20k.... up to 200M.

    You said 50 ohm, so I guess I should use "200"? Or did you mean 50k ohm?
    200 ohms. A out of range reading should read 0L or "1" (on the left side of your multimeter).

    In the board, aside the picofuses there is a 'nromal' fuse, like the one attached on the pic.
    How many ohms should it give?
    All fuses should read 0.3 ohms.

    Leave a comment:


  • capullaco
    replied
    Re: LCD 19" BENQ T905 problems

    Thanks retiredcaps, I gonna check them.
    But one question, which ohm switch should I use? I got : 200,2k,20k.... up to 200M.

    You said 50 ohm, so I guess I should use "200"? Or did you mean 50k ohm?

    Edit:

    In the board, aside the picofuses there is a 'nromal' fuse, like the one attached on the pic.
    How many ohms should it give?

    Edit 2:
    Ok, the picofuse is blown, with multimeter at 200k ohms, it went from ~160 up to 200.
    Attached Files
    Last edited by capullaco; 08-26-2010, 03:14 PM.

    Leave a comment:


  • retiredcaps
    replied
    Re: LCD 19" BENQ T905 problems

    Originally posted by capullaco
    But I saw 2 transistors that seemed to have burnt a bit the board.
    Some browning is normal.

    Well, I had values from both transistors, so Im not sure there broken after all...

    As a last note, I must say that I checked them on board, ie. I didnt desolder them.
    Here is how I test transistors in circuit.

    a) put black probe (com) on pin 1 and red probe on pin 2 - read ohm
    b) put black probe (com) on pin 1 and red probe on pin 3 - read ohm
    c) put black probe (com) on pin 2 and red probe on pin 3 - read ohm

    If any ohm reading is less than 50 ohm you have a shorted transistor and it will need to be replaced.

    edit:

    Some boards will have a fuse or picofuse and they may be open because a transistor was shorted or some other component went bad.

    You can test for open fuses by (with power off and unplugged)

    a) put black probe (com) on one pin and red probe on other pin - read ohm

    If the reading is 0.3 or 0.4 ohm you have a good fuse. Anything higher is a sign of an open fuse. Do NOT replace fuses and turn on the power back on without checking for what caused the fuse to go open otherwise you will just be replacing the fuse again.

    Leave a comment:


  • capullaco
    replied
    Re: LCD 19" BENQ T905 problems

    Ok Im gonna change 2 capacitators that seem a bit out of shape (just a bit, I bet theyre ok, but just in case) and the fuse, that seems is a common problem.

    But I saw 2 transistors that seemed to have burnt a bit the board.
    One just a bit, and the other, you can see the burnt a lot. Also this transistor seems to have a very short middle pin, or its broken, I dont know.
    I have marked it on the pic attached.

    I have checked them with a multimeter, configured it in Ohms, and tested the middle ping with the others.

    Before saying anymore, I have to say that its what I read on Internet on how to check transistors ,so I dunno if I did properly.

    Well, I had values from both transistors, so Im not sure there broken after all...

    As a last note, I must say that I checked them on board, ie. I didnt desolder them.

    Thanks
    Attached Files
    Last edited by capullaco; 08-26-2010, 01:28 PM.

    Leave a comment:


  • retiredcaps
    replied
    Re: LCD 19" BENQ T905 problems

    Originally posted by capullaco
    Im a total noob,but also I like this :p
    I suggest you start by studying this book



    It will walk you through the basics and id all the components on the boards.

    In addition, your pictures are horribly out of focus. Take your boards to a window on a sunny day, use macro mode, and turn flash off. Here is an example of clear focused pictures ...

    https://www.badcaps.net/forum/showpo...08&postcount=3

    Leave a comment:


  • capullaco
    replied
    Re: LCD 19" BENQ T905 problems

    Sry, now I uploaded the images into the forum.

    Im gonna buy a proper soldering iron to do this job, so I havent tried the post #21 advices yet.

    Like I said, im a newb, and also English isnt my main language,so can you help on those points please?

    Code:
    Replace all of the secondary caps.
    You mean capacitators? Or all the electronic stuff in general? How do I get the stuff type/info to buy them in a electronic store?

    Code:
    Desolder all 4 inverter transformers legs and reflow them with new solder.
    Where are the inverters on mi screenies?

    Code:
    Desolder all 4 transistors and the polyester caps (between the transistors) and inductors (nearby the transistors) for the inverter and reflow them.
    Can you mark those on the screenies?

    Im a total noob,but also I like this :p
    Im starting to buy some electronic/soldering items to do those jobs properly, I have on my mind to try to repair this TFT and an old Game Gear

    Thanks
    Attached Files

    Leave a comment:


  • retiredcaps
    replied
    Re: LCD 19" BENQ T905 problems

    Originally posted by capullaco
    Here are some pics,sry for the quality.
    What should I do now?
    Re-read post #18 on how to post pictures. The URLs you supplied show nothing but a postage stamp.

    Did you try testing anything in post #20 and #21?

    Leave a comment:


  • capullaco
    replied
    Re: LCD 19" BENQ T905 problems

    I connected the display, the pc recognizes it, the led powers on and work normally, etc.Except for the no image,it works correctly.
    I tried to put a strong light in front of the display, and couldnt see anything.

    Here are some pics,sry for the quality.






    What should I do now?

    Leave a comment:


  • retiredcaps
    replied
    Re: LCD 19" BENQ T905 problems

    Originally posted by capullaco
    And like I said, im a botcher in soldering and electronics in general

    Any tip for a soldering iron for this kind of jobs? small solderings
    Curious Inventor video on soldering is a really good one.

    http://www.youtube.com/watch?v=I_NU2ruzyc4

    Leave a comment:


  • capullaco
    replied
    Re: LCD 19" BENQ T905 problems

    Sorry I cant post images now.
    I dont have a camera atm (long story) and my mobile phone just broke :/

    But the PCB is the same as the one posted by dvorav.

    And like I said, im a botcher in soldering and electronics in general

    Any tip for a soldering iron for this kind of jobs? small solderings

    Leave a comment:


  • Krankshaft
    replied
    Re: LCD 19" BENQ T905 problems

    My standard operating procedure with these monitors is:
    • Replace all of the secondary caps.
    • Desolder all 4 inverter transformers legs and reflow them with new solder.
    • Desolder all 4 transistors and the polyester caps (between the transistors) and inductors (nearby the transistors) for the inverter and reflow them.
    • Check the rest of the board over with a magnifier for other bad joints.


    If you haven't done all 4 steps in the list you will have a repeat failure.
    Last edited by Krankshaft; 08-03-2010, 03:51 PM.

    Leave a comment:


  • retiredcaps
    replied
    Re: LCD 19" BENQ T905 problems

    Originally posted by capullaco
    No,no display at all, not even the BenQ logo, but the led turns on right.
    Benqs are notorious for blown picofuse, shorted transistors, and poorly solder transformers. I believe you will have one or all 3 of the above if you get no display or Benq logo, but have the power led on.

    Post a pic and we can suggest test points.
    Last edited by retiredcaps; 08-03-2010, 03:28 PM.

    Leave a comment:


  • capullaco
    replied
    Re: LCD 19" BENQ T905 problems

    Originally posted by retiredcaps
    Do you get the screen for 2 seconds and then to black? Or do you get no flash or display at all?
    No,no display at all, not even the BenQ logo, but the led turns on right.

    Leave a comment:


  • retiredcaps
    replied
    Re: LCD 19" BENQ T905 problems

    Originally posted by capullaco
    Hi, I got the same TFT with the same problem.
    One day I was browsing youtube and suddenly the screen was fading to black.
    Now I cant see anything, but the led turns on normally.
    Post pics after reading this FAQ on pic posting.

    https://www.badcaps.net/forum/showthread.php?t=1868

    Do you get the screen for 2 seconds and then to black? Or do you get no flash or display at all?

    Leave a comment:


  • capullaco
    replied
    Re: LCD 19" BENQ T905 problems

    Hi, I got the same TFT with the same problem.
    One day I was browsing youtube and suddenly the screen was fading to black.
    Now I cant see anything, but the led turns on normally.

    Could it be the inverter? Where is it? Which model/type is it (to order a new one)?
    I dissassembled it as far to see the PCB, but I cant see the inverter bar (never seen one outside internet guides btw).


    Im also a noob for electronic stuff, I got a tester but I dont know how to check the items on it.

    Leave a comment:


  • Djadjo
    replied
    Re: LCD 19" BENQ T905 problems

    repaired the monitor few seconds ago....

    mos q812 (9024n) burned when i lit monitor...but it was my fault...after first testing i didnt re-measure c5707 again...so i burned two in total 9024n...and than realize that c5707 died tru first test...

    after that it was easy...changed two c5707 and put new 9024n...and monitor works..without any overheating or any problem..



    Thanks 2All

    Djadjo

    Leave a comment:


  • Djadjo
    replied
    Re: LCD 19" BENQ T905 problems

    sorry, I didnt said exactly what have i desolder...

    ok i have desoldered next components : T801,802,803,804..they all have same instrument readings..the c824 c826 have exact values on lcr metar...
    i have changed c821 elco (470uF 35V) the coils l801 and 802 apears normal too...I didnt touch annything on input part of the board..(the 220V to the mosfet q601...put him out and measure..and seems ok....




    Djadjo

    Leave a comment:


  • retiredcaps
    replied
    Re: LCD 19" BENQ T905 problems

    Just to clarify, did you desolder the transformers? I can't understand what "it" is.

    Originally posted by Djadjo
    i looked the high volt trafos...and everthing of components around or in that circle....i desoldered it and than look on multimeter...everething else is good...

    Leave a comment:

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