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The display on a Toshiba P305D-S8834 laptop is very dim. I bought a LCD inverter and replaced it but the problem is same. When I connect that laptop to an external lcd then display came fine on it. So, will it means that laptop's lcd screen is damaged. Please note that there are no white or black dots on the lcd.

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  • Faheem Ahmed Aug 27, 2010

    I bought a new LCD screen just to avoid changing backlights because I was afraid that may be LCD will damage and according to instructions which you sent me shows that CCFL backlights are in the LCD Screen so by changing an entirely new LCD should solve the problem but after even changing the whole LCD, I have seen the problem is same i.e., DIM display. Now, please note that inverter and LCD screen has been changed. Now, what should I do ? Please advise.

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  • Computers & ... Master
  • 5,103 Answers

Actually it may not be the LCD screen but the backlights. These are sandwiched against the screen on the sides of the LCD panel.. You need to order by length and width and get ones for your screen size. Separate the screen from the bezel. Remove the tape, and separate the reflector (make a note of how things are put together) then you have to Dremel (or use another rotary tool) to remove the plastic to get the backlight out. (They are often molded into the frame.) Then put in the new backlight and reassemble everything. (http://www.lcdparts.net/howto/default.aspx) but for an overview: http://www.inventgeek.com/Projects/BacklightFix/overview.aspx
See http://lcdparts.net/CCFL3D.aspx for backlights for specific brands and sizes of laptops.

BTW: you can check if the new inverter is working with a multimeter. If you borrow (or have a) high-end multimeter (able to measure high frequencies - 50 kHz) or an oscilloscope, hold the multimeter probes a fraction of an inch apart about an inch above the board and power up the TV. If you see a 1 or an actual value, you have a good inverter. If you see a reading near 0, the board is bad or the multimeter can't resolve the frequency.

I hope this helps.

Cindy Wells

Posted on Aug 23, 2010

  • 3 more comments 
  • Cindy Wells Aug 27, 2010

    Can you attach an external monitor to the laptop? (Some will toggle an external monitor on with + + (press all three simultaneously) when the VGA port is active.) This will check if the problem is with the on-board video or with a part of the monitor hardware (ribbon cables, backlight and inverter). Cables can easily come loose or be damaged during the reassembly. Make sure they are all properly seated: http://www.laptoprepair101.com/laptop/20... . Another thing to check is the laptop lid switch that should put the computer into standby when the lid is down. If that is sticky you might get false shutdown issues.

    Did you buy a new screen or a used one? What vendor did you receive it
    from? Did they provide a warranty? Sight unseen, I can't tell if the
    replacement had a good or bad backlight. There are testers available at
    lcdparts.net. A similar issue exists with the inverter - is the
    replacement working? (an oscilliscope with probes held about an 1" above
    the board and a fraction of on inch apart works as well as the testers
    for diagnosing the inverter.) A free-standing backlight can check the
    inverter if it is a known good part.


    The backlight isn't really in the screen. The screen has many layers - glass, LCD sheet, other parts. The backlight gets crowded into the edge between the layers. See this for a different set of pictures: http://www.laptoprepair101.com/laptop/20... .

    Cindy Wells


  • Faheem Ahmed Aug 27, 2010

    Dear Cindy,

    Please note that when I attach an external monitor then image came normal on it. On this Toshiba laptop, it requires "Fn F5" key combinations to switch monitors and the image is normal on external monitor but again dim on LCD of laptop and both new and old LCD screens have same result and new and old LCD inverters also have same results. I even tried to increase the brightness but it was also not working. As I told you the purpose of getting new LCD screen was that I don't want to play with CCFL Lamps and as per my understanding, with new LCD, the CCFL lamps will also be fine and also please note that both items are new (not original Toshiba but their OEM compatible).

    So, now I am a bit confused what to do ? What thing could be wrong.

    Thank you in advance for your help and co-operation.

  • Cindy Wells Aug 27, 2010

    I wasn't sure if you still had the external monitor on the laptop. That's why I asked.

    When you ordered the new inverter, did you match the Rev number for the part? I've seen a few mismatched inverters that had the contrast control reversed. You can try lowering the contrast and seeing if that brightens the laptop screen (while the external monitor dims).

    Since all the parts are new, I'm not sure what is wrong. You could have either a bad cable or one of the new parts from the OEM manufacturer are faulty.

    Additional testing is probably needed. This is probably time to invest in a lcd tester. oscilliscope/mulitmeter (only tests the inverter) or at least a spare backlight and inverter. Use the spares to test the LCD screen and inverter without the laptop being reassemble. Alternatively, a visit to a shop with an lcd tester. (I've found online shops that specialize in lcd screen repairs but I'm not sure how close they are to you.http://www.moniserv.com/doc/inverterrepa... orhttp://www.lcdrepair.us/ )

    Cindy Wells

  • Faheem Ahmed Aug 29, 2010

    Dear Cindy,

    I don't have anyone nearby in Baltimore who have LCD tester but I experimented something which I want to discuss with you.

    As I told you I have now one new LCD screen and one new inverter. First I tried new LCD screen with old inverter and then new inverter but the result is same i.e., dim or too dark display. Meanwhile I attached external monitor and it was fine. Then I again attached the old screen but forgot to attach any inverter and put the laptop on and found that the screen is still displaying in a dim mode then I tried new screen without inverter and got the same result.

    Now, my question is it possible to get display without LCD inverter and also will it means that problem is only in the inverter and both LCD's are fine.

    Please advise me with your precious comments.

    Thanks

  • Cindy Wells Aug 29, 2010

    Unfortunately, that test (running the laptop screen without the inverter) can only tell you if the video signal reaches the screen and if the LCD pixels are active. (Even that could be difficult to resolve since most can't see a lit pixel without the added light behind it from the backlight.) It won't tell you anything about the backlight or the inverter. The backlight and inverter are paired; they are the equivalent of a full-length fluorescent tube and the ballast of a fluorescent light fixture. The backlight is driven by the inverter and can't light without it unless you put it near another source. (There is an old physics demo for lighting a fluorescent tube without the ballast - get the pins near another current source.)

    A multimeter that can measure high frequency (or an oscilloscope) would be a much better way of testing if either inverter is working. Similarly a backlight that you aren't going to install can test the inverter if you know it is a good backlight. Then you can assume it's a bad backlight if the inverter passes the test (whether it be the lighting the spare backlight or producing the high voltage with phase change). The lcd testers are just convenient tools for those who do a number of the tests since it can check the backlight or the inverter separately and is faster than the multimeter test. (There are some who try to test the inverter board with a multimeter but because of the high voltage the hover test is safer.)

    Fluke sells a multimeter which can handle the frequency of modern laptop inverters. (Oscilloscopes can be found in many academic laps in the engineering or physics department. You can ask at a local high school about borrowing one (or bringing your parts to the school for an afterschool demo and test). I happen to have access to the oscilloscope at home so I only have the basic multimeter.)

    There is a way to get the screen lit without the inverter and backlight combination. Take an old CRT monitor, take it apart and replace the guts with a light bulb and place the LCD screen in front of the bulb. http://www.ccs.neu.edu/home/bchafy/monit... has the details on this hybrid. However, that is only really useful for fixing a broken external monitor and not a laptop screen.

    Cindy Wells

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