10-02-2011 12:25 PM
I've several IBM ThinkPad T21. In general, if you close the lid the backlight turns off. But I have two T21 where these feature does not work; the backlight reminds on. All my laptops have the same BIOS settings and the same Windows 2000 installation.
To my amazement, if the lid is open and I press the thin button on the right upper corner of the keyboard (the button which is pressed if the lid is closed) the backlight turns off. But if I close the lid a little bit more and then press the thin button the backlight doesn't turn off.
With other words: if the lid is open more than 90 degree (angle between keyboard and display) the backlight turns off and if the lid is open less than 90 degree the backlight doesn’t turn off if I press the thin button.
To my big surprise the angle which changes the behavior of this thin button is exact 90 degree (on both laptops!!!).
I have absolute no idea why these two T21 have this strange behavior while all my other T21 don't and why it depends on the angle of the lid.
Any clue is very appreciated because these T21 are planned to be used with a closed lid and a turned off backlight.
10-05-2011 08:01 PM
10-05-2011 10:06 PM
Automobile trunks and hoods used to use "mercury" switches, a cylinder with two contacts filled with some mercury, and when gravity forced the mercury to hit the contacts, the circut was complete. It almost sounds like your thinkpads have one of them that is dislogded lol *joking of course*.
I honestly don't know how these models switch the display on/off, but it sounds like they have two redundant switches, and one of them has reversed its function. I'm very curious though and would like to know what you find out.
ps mercury switches ere outlawed ages ago due to ground water contamination if the car was wrecked. Nothing like a wrecked car leakng toxic waste, good thing computers don't do that when they crash
10-06-2011 06:04 AM - edited 10-06-2011 06:05 AM
T21 habe mechanic switches.
The behavior can depend on a sticking switch.
Take a look under the keyboard bezel and check the switch and the visible "nose" in the bezel. If the bezel is broken left or right of the keyboard it also may cause the problem since there can be annother damage which is not visible from the outside.
11-06-2011 05:08 AM
First of all thanks for your replies.
In the meantime I did some more troubleshooting. I detached the laptop monitor from the laptop and attached only the wide monitor cable to the laptop. Then I realized that I wasn't able the turn off and on the backlight if I bend the cable more than 90 degree. That means that I can't fix this problem because I'm not able to repair this cable :-(