12-05-2011 03:17 PM
I've just bought a new T420s and installed Debian GNU/Linux on it. Had no screen problems the first few days.
This morning when I turned it on, the screen was flickering -- like it was doing a very slow refresh rate or something. Extremely noticeable, and quite annoying :-). Interestingly, the flicker started from the moment the screen came alive, when I turned the power on. It persists through the boot loader sequence and into the operating system, etc. I have powered the machine off and back on several times since then, but the flicker is still here.
Now, there is one interesting fact:
The last thing I did, right before the flicker started, was use the laptop with a dock + external monitor. Not dual monitor, just a single external monitor -- the laptop's lid was down when it was in the dock. The external monitor worked fine; at one point I opened the laptop's lid just to see what the screen looked like (I was curious because the external monitor's dimensions were very different from the T420s screen dimensions). The laptop screen had garbage on it -- a kind of distorted, miscolored, and mis-aligned version of my usual operating system desktop. But that didn't bother me -- I was using the external monitor, and didn't need the laptop screen for anything. I closed the lid and kept working.
That night I powered it down in the dock. This morning I packed it up and took it to work. The first time I powered up, this new flicker was there.
Does it have something to do with the fact that I used it with a dock and/or external monitor? It seems suspicious that the problem started right after the first time I did that.
By the way, this is a T420s with the stock video card, not the fancier Nvidia card.
Any ideas how to fix this?
12-07-2011 07:40 PM
12-07-2011 09:59 PM
Serge1410, thanks for the reply. I don't have any obvious way to restore the original OS (maybe there is a CD in the box, back at my office?) but in any case this morning the touchpad stopped working in some circumstances too. While it's possible that the OS is the cause of both problems, I finally decided I couldn't afford to spend any more time dealing with this, and I called Returns. They were extremely helpful and prompt, I'm pleased to say, and I'm just sending the thing back. I will try the X220 instead, which gets good compatibility reports for Debian GNU/Linux.
12-07-2011 10:03 PM
By the way, regarding the screen flicker issue: I also tried updating the BIOS to version 1.30 (8CET50WW, 2011/11/11), but that had no effect on the problem. I tried various combinations of Fn+F7 and external monitor (with and without docking station), and the Debian GNU/Linux "xrandr" and "xvidtune" programs, and the "enable_mtrr_cleanup" boot-time option to the kernel. None of these restored the machine to the non-flickering state it was in right after I first installed Debian.
05-03-2012 10:57 AM
I'm seeing the exact same problem (extreme flickering from the moment the screen turns on), and I'm now logged into Windows7, running the ThinkVantage diagnostics tests but they all passed so far.
Did you find anything else about this, Karl?
05-03-2012 11:44 AM
We have several T420's where I work and have had several repaired under warranty due to the screens and fans. Not that this helps your problem but FYI.