VERY dim LCD on a T21

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Wingnut · #1 Post by **Wingnut** » Thu Jun 12, 2008 9:24 am

I have a friend with a T21 that has a very dim LCD. It looks almost as though the backlight is gone as you can barely see the IBM logo on the splash screen. So my first test was to swap in a known working LCD from one of my spare parts T23's. Still no change. I then swapped inverters and still no change. The display works perfectly on an external monitor, so I guess the video chip is good.

So my question is, if it is not the LCD and its not the inverter and its not the video card, what could it be? The ribbon cable? I would have though that since the information is getting to the LCD, that the ribbon cable would be good? Its just really dim. I did do a search in the T2X forum for "dim LCD" but could not find anything similar to his problem.

Thanks for looking

#2 Post by **RealBlackStuff** » Thu Jun 12, 2008 9:57 am

The signal to the VGA port (external monitor) is analog, the signal to the LCD is digital. These are different signals! If one works, the other need not be good. Try another LCD-cable. The XGA cables for all T2x can be used, even if they look different.

Wingnut · #3 Post by **Wingnut** » Thu Jun 12, 2008 10:12 am

Thanks for the reply. I just find it weird that the information is getting to the LCD just fine. I can barely see it, but it is there. That is why I thought it was the backlight or the inverter. But it can't hurt to try another cable I guess. I'll give it a shot tomorrow when I have more time.

Thanks again.

SMA · #4 Post by **SMA** » Thu Jun 12, 2008 3:09 pm

It is the law of nature that every piece of metal will end up breaking, if it sufficiently often, is taken through the exercise of
bending and unbending.
This is what happens to the LCD cables when they starts failing. One or more wires inside the cable break.
It is not visible from the outside and therefore it is rather hard to believe.

Actually, such a cable will have to bend more than 90 degrees, each time the lid is opened.
In the case of the cable used in t20 and t21 ThinkPad's, it is the wire running at the far right side, that will break first and
it will break right there where the cable is bending the most.

It is possible to verify if this is the case. Read about it here.
There is a description and some pictures in the last post by Robbyrobot.

#5 Post by **rkawakami** » Thu Jun 12, 2008 3:59 pm

Beside the backlight, inverter and LCD ribbon cable, the other sources of possible problem in the T2x for no backlight are:

- stuck lid switch
- defect on the I/O board (what the lid switch is mounted on)
- motherboard

Wingnut · #6 Post by **Wingnut** » Fri Jun 13, 2008 9:25 am

Wll, I will eat some crow and send thanks out to RealBlackStuff....it was the ribon cable it seems. I took one from a parts T23 and it seems to have done the trick.

Thanks very much everyone for your input.

#7 Post by **RealBlackStuff** » Fri Jun 13, 2008 9:59 am

You're welcome and enjoy your meal

VERY dim LCD on a T21

VERY dim LCD on a T21

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