Question about Computers & Internet
Posted by Anonymous on
I had the same problem with a Toshiba A105 laptop and was able to fix it. Up front, I have to say that:
1) You shouldn't try this unless you have some expertise in fixing electronics and are comfortable disassembling laptops. Especially since it involves working with the LCD inverter board which provides high voltage to the fluorescent backlight tube.
2) Though the symptoms may seem similar, your problem may not be what I found. So keep that in mind.
Just before LCD went into negative image mode, I had noticed a few times when the screen would seem to darken intermittently, I thought maybe the power cord was loose and the system was falling into a power save mode but now I think this was the warning sign.
When the failure occurred it was immediate and never recovered. At the time, I thought the backlight had crapped out. But after disassembling the lid and re-powering I could see the backlight shining from the back of the LCD assembly. I then checked for loose wires and cabling connections with no luck. Finally, since the inverter was covered by a thin plastic cover, I started pressing lightly on parts of the inverter board for bad solder joints and cracked traces. Bingo! I was able get the screen back by pressing on an SMT potentiometer with the reference designator VR1. I threw an ohmmeter across the outside leads and found it was 10K but the measurement from one side to the wiper was only about 500 ohms. I tried to de-solder the pot but it cracked and broke during the effort - very fragile. Since I didn't have a matching part, I replaced it temporarily with a 10K 10-turn through-hole part just to find a good setting. I went with about 1200 ohms by turning and eyeballing the contrast of the screen, though it was pretty subtle. I removed the pot and substituted two 0604 chip resistors to match the pot setting. Powered back up and it works like a champ. Though, as I said before, your mileage may differ.
Posted on Oct 02, 2010
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Posted on Jan 02, 2017
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