[Tfug] Swapping out a notebook's LCD?

[Bexley Hall]

Hi Claude,

--- On Sat, 10/11/08, Claude Rubinson <rubinson at u.arizona.edu> wrote:

> So, I received my new thinkpad the other day.  I had a T40 and went up
> to a T42, so it's basically identical.  I just swapped out the hard
> drive and everything was the same.
> 
> Well, almost everything.  I accidentally purchased a T42 with the
> 1024x768 resolution LCD rather than the 1400x1050 resolution.  The LCD
> is fine on my old machine, so I'm wondering if I might be able to swap
> them?
> 
> I took apart the dead T40 and the LCD was pretty simple to remove (a
> few screws and had to disconnect on connector).  So, physically at
> least, I don't think that it should be a problem.
> 
> Is there anything that I need to think about/research before going
> ahead with this?  Are there any problems that I'm not aware of?
> 
> One issue that I am concerned with is that Xorg now probes the monitor
> for its maximum resolution and respects that setting.  Does anybody
> know if that information is stored in the LCD itself?  Or might it be
> outside of it?  (In which case, swapping out the LCD won't do me any
> good.)  (Also, just to stave off any confusion--it is definitely the
> monitor's resolution that's the limiting factor here, the built-in
> video card is capable of driving much higher resolutions.)

Let me preface this by saying that I haven't looked at any LCD
*panels* (i.e., the actual display component) in a design in many
years...

But, if you are thinking of *just* swapping the panels, I think
you will find no joy there.  The panel itself doesn't "tell"
the controller its resolution, scan rate, etc.  Rather, the
controller is programmed to drive it *at* a certain resolution,
scan rate, etc.

So, unless you can figure out how to tell the "BIOS" what the
characteristics of this monitor are, it will continue to tell
the controller to use the parameters appropriate for the "old"
(original) panel.  The results here could vary from:
- original image resolution displayed in a corner of the new panel
- no video at all
(I doubt the panel would suffer any permanent damage -- assuming
the absolute maximums on voltage, etc. are satisfied -- though I
make no guaranees!  :> )

As a result, you run the risk of breaking "something" in your
disassembly/reassembly process with little *probable* gain.

By way of a (strained) example:

Take a random (non "plug n pray") monitor and hook it up to a random
computer.  Then, try driving it at 1600x1200.

"Oh, gee... this is a monochrome monitor!  Why didn't the computer
*know* that?"

"Oh, gee... the dot pitch on this monitor is such that anything
above 800x600 is a blur"

"Oh, gee... the horizontal deflection amplifier can't handle
that HSYNC rate and now the HOT is blown (i.e., replace monitor)"

I.e., a monitor, in and of itself, can not be "probe()-ed" to determine
it's capabilities.  Likewise for the LCD *panel*.

I'm not sure of any deterministic means you might have available
(besides empirical testing) to verify this a priori.  If you have
access to detailed (service/parts) manuals for the T42 with
"your" display and the "better" display, see if they mention
any differences in part numbers for anything OTHER THAN the panel
itself (i.e., obviously the panel will be different; but, will
they also specify a different main-board assembly... necessitated
by a different BIOS ROM?!). Of course, it could also be that
the manufacturer has a "secret utility" that they use on the
production floor to configure the BIOS for that particular
model to specify the panel configuration that is actually
*installed* in the unit at time of manufacture...

<shrug>

You have to do a probablistic cost-benefit analysis -- what's the
value of the upgrade to you, what's the potential loss you might
incur in the process (max = cost of machine + value of your time)
weighted by your estimates of success/failure/loss.

Personally, if it was a "spare" machine, I might play with it
as I wold enjoy learning from the experience.  But, if I
wasn';t willing to lose the time/hardware, I'd just kick
myself for buying the wrong unit and live with it until time
for another upgrade (which is pretty often with laptops :> )

I'm sure we'd all be curious to hear the results!

G'Luck!
--don