[Thinkpad] A21p backlight won't stay on

[Michael Geary]

My A21p has developed a problem with its backlight, naturally a couple of
months after it went out of warranty.

The machine powers on normally, and the display looks fine with a good
bright backlight, but after 10-15 seconds or so, the backlight goes off.
This happens either running an OS or simply at the power-on screen, so it's
not a software problem. I tried taking out the main battery and unplugging
the CMOS battery for a while, but that didn't help.

If I boot into Windows, and after the backlight goes off I use Fn+F3 ("turn
off monitor") and then hit the Fn key again after a few seconds, the
backlight comes back on for another ten seconds or so and then goes off
again.

There's no reddish tint or any other symptoms. The backlight looks fine when
it's on. It just won't stay on.

Anyone have an idea of what component might be at fault here? I've got a
spare A21p system board, but I don't want to replace it if the problem is
likely to be something else.

Thanks!

-Mike