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how to physically disable T400 lid sensor(s)?

Posted: Sat Nov 16, 2019 11:40 am
by GNUser
I have a T400 laptop on which I run various GNU/Linux distributions. I need help to *completely* physically disable the laptop's lid switch/Hall effect sensor(s).

The trouble is that my tests lead me to believe that the laptop has two lid sensors, but I can only locate one.

I've found that taping a tiny magnet just above the bluetooth LED disables a lid sensor: Without the magnet, the output of the command below is "open" or "closed" depending on whether the lid is open or closed; with the magnet in place, the output of the command below always "closed" (even when lid is physically open):

Code: Select all

$ cat /proc/acpi/button/lid/LID/state 
state:      closed
So far so good.

Here is where it gets weird: Even with the magnet in place, xscreensaver only kicks in when the lid is physically open, partly closed, or almost closed. If the lid is fully closed, xscreensaver absolutely never kicks in. This makes me think that there must be a separate sensor elsewhere, but for the life of me I can't find it. I've used multiple magnets and have moved them around practically everywhere (on and around the display, on and around the keyboard, everywhere around the palm rest, around the hinges). No matter where I put additional magnets, xscreensaver consistently kicks in only when lid is open, never when lid is closed.

I'd like to *completely* physically disable the T400 lid switch sensor, so that all applications behave exactly the same way regardless of whether the lid is physically open or closed.

Please, where are the lid sensor(s) on the T400? How do I completely disable them?

Re: how to physically disable T400 lid sensor(s)?

Posted: Sat Nov 16, 2019 8:38 pm
by thinkpadcollection
Only one sensor for closed when magnet is next to this turns LCD off.

To disable, take the bezel off the LCD lid and locate the magnet and simply take it out. Put bezel back on. This will meet your needs. Or in the keyboard bezel assembly, takes HMM document to disassemble this T400 to find the magnet.

Cheers, thinkpadcollection.

Re: how to physically disable T400 lid sensor(s)?

Posted: Wed Nov 27, 2019 3:03 pm
by GNUser
I discovered that the lid switch sensor I had found (above bluetooth LED) is the only one. Applications that wait for system to be idle were not kicking in while lid is shut because of random touchpad activity that occurs when the lid is closed and screen is close to the touchpad.

The secret was the following:

1. Disable the lid switch
Either by sticking a little refrigerator magnet just above the bluetooth LED or, via software, with this:

Code: Select all

sudo sh -c 'echo PNP0C0D:00 >/sys/bus/acpi/drivers/button/unbind'
sudo sh -c 'echo PNP0C0E:00 >/sys/bus/acpi/drivers/button/unbind'
AND

2. Disable the touchpad
By unplugging its ribbon below the palmrest. Trackpoint and its three buttons (just below the spacebar) work just fine with the touchpad's ribbon disconnected.

Now all applications behave exactly the same way, regardless of whether laptop lid is open or closed.

Re: how to physically disable T400 lid sensor(s)?

Posted: Wed Nov 27, 2019 7:36 pm
by shawross
GNUser wrote:2. Disable the touchpad
By unplugging its ribbon below the palmrest. Trackpoint and its three buttons (just below the spacebar) work just fine with the touchpad's ribbon disconnected.
Trackpad can be disabled in the Bios which happens to every Thinkpad that I own.

Re: how to physically disable T400 lid sensor(s)?

Posted: Tue Dec 03, 2019 2:05 pm
by GNUser
"Trackpad"? There's a Trackpoint and Touchpad, no "Trackpad". Touchpad was the bad guy here, generating random input when lid is closed.

Agreed that disabling Touchpad in BIOS is a great alternative to unplugging the ribbon. However, I use Libreboot instead of BIOS; alas, Libreboot does not have the option of disabling the Touchpad.

Re: how to physically disable T400 lid sensor(s)?

Posted: Tue Dec 03, 2019 2:09 pm
by dr_st
GNUser wrote:
Tue Dec 03, 2019 2:05 pm
"Trackpad"? There's a Trackpoint and Touchpad, no "Trackpad".
"Trackpad" is commonly used as a synonym to "touchpad".

Re: how to physically disable T400 lid sensor(s)?

Posted: Sat Dec 14, 2019 1:32 am
by Ignorant
THis post may be in wrong place..but it is nearest to what i was looking for.
I paid a queens ransom and got my t400 working again......
The strip lights on (bottom of the lcd ,just above the keyboard) do NOT blink...any of them...
The laptop works fine otherwise.
any suggestions....documentations ....
does any verson of linux support the graphics chip on my t400 (p 8400 , WXGA +) which is probably a 3470... :
:x

Re: how to physically disable T400 lid sensor(s)?

Posted: Sat Dec 14, 2019 1:35 am
by Ignorant
Cheers, thinkpadcollection.
dear where are the documents which describe the lcd sensors.? :oops: