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mf_nicecub

Member

Registered: 2022-01-26

Posts: 4

Thinkpad T460 backlight wont turn on for minutes after boot/sleep

I've run into a strange problem this past month where my screen doesn't seem to wake from sleep/at boot (I don't even see the boot splash screen/GRUB at boot). No sign of the screen's backlight being on. External monitors work fine. Generally, the backlight will come back on after several minutes. Brightness control buttons have no effect, same with manipulating

/sys/class/backlight

.

When the backlight (randomly) comes back on, if I reboot/wake from suspend, the backlight will work for a short while, until I leave my backlight off for a long period of time (either by shutdown or suspend), when the issue will return.

Here's my dmesg for a couple min after a boot where my backlight works properly: https://pastebin.com/QMGdhzuR
Here's a dmesg for when my backlight won't turn on: https://pastebin.com/U3KdWBji

Nothing there jumps out at me.
As you can tell from my dmesg, I've tried fooling around with some kernel params like

i915.enable_dpcd_backlight=1 acpi_backlight=vendor thinkpad-acpi.brightness_enable=1

, but no luck.

I don't seem to have any firmware updates available if that's relevant. Wondering if issues like this might be related: https://gitlab.freedesktop.org/drm/intel/-/issues/5027

Are there are good next steps I could try? Would flashing my BIOS do anything? Could this possible be a hardware issue?

ewaller

Administrator

From: Pasadena, CA

Registered: 2009-07-13

Posts: 20,690

Re: Thinkpad T460 backlight wont turn on for minutes after boot/sleep

Is this an LED back light? Or is this old enough to be a cold cathode florescent (CCF) back light?   Sounds like inverter issues from days of yore.

As a data point when the display is off and should not be, darken your room and illuminate the display from a highly oblique angle with a flashlight (torch) from the side, then from another not quite so oblique angle look at the display from above.  You may be able to see the LCD running in reflective mode instead of transmissive mode.   If it is not blank, then at least we know the display is being presented.

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mf_nicecub

Member

Registered: 2022-01-26

Posts: 4

Re: Thinkpad T460 backlight wont turn on for minutes after boot/sleep

Ah thank you! I've tried shining a flashlight on the screen before, but doing this in a very dark room was key. I do indeed see a display reflecting very faintly. Could this still be a software/firmware/acpi problem at this point, or is this most likely a hardware issue? FWIW, poking around online the thinkpad 400 series seem to be LED backed, not CCF.