[lug] Laptop screen snow affected by software?

[Chris Riddoch]

My laptop (an old and gradually dying T4 Thinkpad) started doing
something interesting late last week - I'm getting snow on the screen,
after X has been running 10-20 seconds.  Of course, my natural
assumption is a failing connection between the screen and the rest of
the system.

Here's the weird thing: when I plug the laptop into an external
monitor, X goes into what appears to be a lower resolution, puts the
display up on both external and built-in screens... and the snow
completely disappears from the laptop display!  Evidently, there's
something software-related about this snow, which strikes me as odd,
given the likelihood that it's really just a bad cable.  Back in the
days of CRTs, snow would come and go at different resolutions until
the proper X settings were arrived at - it makes sense, after all, the
connection between the two was rather analog.  But on a laptop screen,
where the display hardware has a lot more control over the pixels,
snow suggests connection problems to me.

So my question: Just how can snow on a laptop screen be affected by
*software*?  Any suggestions, besides the obvious "buy a new laptop"
(which I'll do as soon as finances allow, of course.)  Looks like I
won't be at 1400x1250 again anytime soon.

-- 
Chris Riddoch