diagnosis of symptoms on a Thinkpad A21m LCD

[gdement]

Laptop is an IBM Thinkpad A21m (maybe A22m, not sure, and it actually has an A20m motherboard in it. A20-A22 are the same thing anyway)
Type 2628, 14" 1024x768 screen
According to IBM data, it could be either a "PBU" brand screen (05K9578) or a Samsung (05K9588).


My sister has asked me to look at fixing her laptop screen. My first assumption would be the backlight, but I'm not really sure as I've never seen what that looks like first hand, and the behavior seems a little different:

The general complaint is that it tints red intermittently.
If she hits it then it will often go back to semi-normal. If she presses at the back it will turn red all over.
When working semi-normal, then the darker colors look fine but the lighter ones are still somewhat tinted. So it never really looks quite right.

A few months ago she first showed me the problem. At one moment I remember seeing a high resolution noise pattern of red horizontal lines that appeared near the right side of the screen, then went away. I think the lines' left edges were aligned but the right edges were changing length at random. It wasn't a general glow, they were lines. But it's been a long time since I saw that and my memory of it is fuzzy.

Her son is a toddler, and has stepped on the laptop a few times.


My understanding is that the inverter would just cause it to go dark, not turn red. Is that correct?
The flaky behavior makes me wonder if it's a bad connection somewhere. But backlights are what's best known for causing red tints.
Does this sound like a typical backlight problem, or is it something else?


Thanks. I have little experience with LCDs, other than recapping a desktop version.

[Wizard]

Re: diagnosis of symptoms on a Thinkpad A21m LCD

LCD is the fault, unfortunely.

And what the heck using this, i'm curious? This is very old PIII (max 900MHz) system and picky about memory (discovered to my dismay).

I have one also for FreeNAS, as I can't beat on it with 2000 or XP with 256MB because I can't justify paying lot for second 256MB SDRAM.

Either find newer used notebook (thinkpads is still a king) or replace LCD (does not make sense for older system).

Cheers, Wizard

[NxB]

Re: diagnosis of symptoms on a Thinkpad A21m LCD

I'd check the LCD cable first. A damaged/loose cable will sometimes do this. Definitely not a backlight problem since it doesn't go dark. The inverter only controls the bulb. Otherwise its the panel and unless you have one that will fit its probably not worth fixing. T21-T23s are pretty cheap. Then again a new motherboard for my X21 was only $30 shipped. Check ebay.

[Wizard]

Re: diagnosis of symptoms on a Thinkpad A21m LCD

LVDS IC even video chipset muxes all RGB in 6, 7 or 8 bits per color and go through LVDS interface then on other end LCD internally demux these and do it's job.

If there are bad connections via LVDS, the image will break up regardless of color and usually vertical pinstripes. If fault is only particular color of bad lines it is either mainboard or the LCD.

Cheers, Wizard

[Scenic]

Re: diagnosis of symptoms on a Thinkpad A21m LCD

well... it's the LCD..

rather common problem on older Thinkpads (i've seen lots of those with a red tint on ebay..)

got an old Thinkpad 570 (PII 366) with the same problem.
the red tint goes away (mostly) when warmed up a bit.


if your LCD is a standard 14,1" XGA (1024x768 px) it would be possible to get another LCD on ebay...
just search for those LCDs and look if the connector fits and its LVDS (not TTL)
this *should* work in most cases..

did the same thing on a Toshiba laptop (had a cracked screen, but still showed something in the upper left corner).

exact same LCD was too expensive, so i did the above thing and got a different 14,1" XGA LCD on ebay.
worked fine (and still does). the only thing i had to do was to replace the plug of the backlight CCFL with the one of the cracked screen..

unfortunately, that doesn't work out on my Thinkpad 570, because its a 13,3" XGA display... those aren't so common as the 14,1" ones and because of that, rather expensive. (new display costs more than the laptop is worth when full functioning..)

[gdement]

Re: diagnosis of symptoms on a Thinkpad A21m LCD

Got more information from a phone call - apparently the screen now has 2 permanent horizontal red lines on it. The upper one is thicker, bottom one is thin. I haven't seen it myself.

LVDS IC even video chipset muxes all RGB in 6, 7 or 8 bits per color and go through LVDS interface then on other end LCD internally demux these and do it's job.

If there are bad connections via LVDS, the image will break up regardless of color and usually vertical pinstripes. If fault is only particular color of bad lines it is either mainboard or the LCD.

Interesting - so I won't hope for a bad connection then. Image is fine on an external monitor but those are probably different signal paths. I guess it's pretty obvious to be the LCD though.

Thanks for all the info, I'll assume the screen has to be replaced... when I looked at that a few months ago it seemed they were available on ebay for about $100 or so. I'll have to look back into it.
But if all I can find are new $500 screens then that won't be worthwhile.

if your LCD is a standard 14,1" XGA (1024x768 px) it would be possible to get another LCD on ebay...
just search for those LCDs and look if the connector fits and its LVDS (not TTL)
this *should* work in most cases..

It is in fact a typical 14" 1024x768, so I'm hoping it will be cheap to replace. Don't know anything about LVDS/TTL, but I'll look it up.

Definitely not a backlight problem since it doesn't go dark.

Generally speaking, isn't red tinting the first stage of failure before it starts to go dark? I thought I read that somewhere but haven't had direct experience.
But regardless, in this case I guess the bulb can't explain moments where the red is sharply defined instead of being a general glow.

And what the heck using this, i'm curious? This is very old PIII (max 900MHz) system and picky about memory (discovered to my dismay).

I don't think using older laptops is that unusual. She had a P-133 up until 2-3 years ago (now that really was slow).
Memory is just standard 440BX requirements - it needs 16Mx8 ram chips. But you're right those type modules do cost more to get.

Her laptop has a 900MHz P3 and 512MB ram, it performs well by my standards but I guess it depends what you're used to. My laptop is an older Celeron 550MHz model of the same series, so it's about twice as fast as mine. New (good) laptops are expensive, and for most things an older one works fine.

Laptop was bought used 2-3 years ago, had shipping damage so the seller replaced the screen. After getting it back, I found it also had a motherboard problem so I replaced it with an NOS A20 board, and updated BIOS to run the late stepping (cD0?) 900MHz CPU at full speed. (That's an undocumented feature of the BIOS, IBM didn't mention it in the release notes but it does add support for those.) It even has a good battery, thanks to finding an NOS on ebay at one point.

T21-T23s are pretty cheap.

My brother used to have a T23. It's not enough faster to get excited about, and it doesn't have a built-in floppy drive. She's one of the few people (like me) who still care about that. Don't use it often but when you want it and it's not there, it's annoying.

I hesitate to buy laptops on ebay because 2/3 times I've done that, the laptop has turned up with significant defects that needed repair. It's like replacing a used car - you know the condition of the old one, but the new one always has surprises.
I'm afraid getting a quality replacement would just cost too much right now.

Thanks everybody for the help.

[kc8adu]

Re: diagnosis of symptoms on a Thinkpad A21m LCD

many ccfl tubes go pink as they die.
this is worse when cold.
its the mercury being lost and more light from the fill gas which is neon/argon.
the mercury gets tied up in the glass and phosphor.

[Wizard]

Re: diagnosis of symptoms on a Thinkpad A21m LCD

I haven't seen a LCD go pink/reddish yet from dying CCFL tubes so I'm curious. Dimming yes, for sure.

Cheers, Wizard

[Scenic]

Re: diagnosis of symptoms on a Thinkpad A21m LCD

I haven't seen a LCD go pink/reddish yet from dying CCFL tubes so I'm curious. Dimming yes, for sure.

Cheers, Wizard

http://bambooz.pytalhost.net/Proview/DSC07067.JPG

19" Proview Widescreen.. common problem..

[Wizard]

Re: diagnosis of symptoms on a Thinkpad A21m LCD

How old is THIS!?

Cheers, Wizard

[Scenic]

Re: diagnosis of symptoms on a Thinkpad A21m LCD

those CCFLs? not even 3 years..

[Wizard]

Re: diagnosis of symptoms on a Thinkpad A21m LCD

Screwed. Lot of stuff I work on are OLDER than 3 years and no pink that why the comments and surprise.

Or unless this monitor/ other cheap panels is using subpar CCFLs or driven too hard.

Thanks for pics!

Cheers, Wizard

[NxB]

Re: diagnosis of symptoms on a Thinkpad A21m LCD

My brother used to have a T23. It's not enough faster to get excited about, and it doesn't have a built-in floppy drive. She's one of the few people (like me) who still care about that. Don't use it often but when you want it and it's not there, it's annoying.

I've had good luck with ebay and laptops but I try to get corporate castoffs from larger sellers. Its a light pink vs red and image distortion issue. The lines seal it, its the LCD.

I don't use floppies because they tend to stop working and a flash drive works much better. All of my floppies die after only a few uses so I'd never store anything important on them. My x21 doesn't even have a cd drive and I can live without. An external floppy drive is also an option.
T23 also has a swappable bay floppy drive. It may not be that much faster but not a bad choice vs an older laptop that's falling apart. If you can find one of the T2x series with the CPU coils falling off, you can make out like a bandit.

[gdement]

Re: diagnosis of symptoms on a Thinkpad A21m LCD

I'm now using the laptop.
Turns out the lines are gray, not red.
They're horizontal, and extend from edge to edge. Slightly below the center of the screen.
I count 4 lines, some thicker than others, very close together.
The lines are mostly dark gray, but they change to lighter shades in some spots toward the right. The coloration is consistent along each of the lines, ie for a given X coordinate the color is the same on each line. Sort of like vertical banding, but only affecting the lines that are dead.

My sister routinely hit the sides of the monitor to clean up the intermittent red glow, and she says the last time she hit it too hard which caused the lines to appear.
I asked if she hit it at the level where the lines are, she says "probably".

I'll try to post pictures when I find a way to get them off the cell phone.

I'm probably going to get a screen from a similar laptop on ebay, but posting the above in case it makes any difference to the diagnosis.

Given the cause, I suppose these lines are a new, separate problem from the intermittent red glow it already had. Between my nephew walking on it and my sister hitting it, I think this screen has had enough.