PowerBook 540c LCD "Grid"

[alk]

My PowerBook 540c has a grid on the screen. It's as if there is a white border around every single pixel, so the overall effect is a "screen" or white grid. The PowerBook seems completely normal otherwise, and the whole display does seem to be visible with no other artifacts. Having no experience with early color LCDs, I kind of just assumed this was a normal feature of that vintage of LCD. I almost feel stupid for asking, but is this normal?

Peace,

Drew

 

[tomlee59]

Interesting...my 540c does not look the way you've described. It could be that there were multiple screen vendors, so what you're seeing could very well be normal. I just haven't looked at enough 540s to say. Since your display functions well otherwise, it probably is normal.

The screen on my 540c has dark vertical stripes (very narrow), and barely visible horizontal ones. I assume that these are routing channels for the pixel transistors. It's easy to imagine that some other panel supplier used a somewhat different layout, leading to more noticeable routing channels. But that's just a guess.

 

[equill]

Neither of the above descriptions is familiar to me, and I have three TFT screens on 520c and 540c Macs. In my experience, the colour TFT displays of the PB 500 series, as opposed to the entirely expectable behaviour of the FSTN displays, are exemplary both for themselves and as products of their time. Even the pointer submarining of the latter is able to be ameliorated, if not overcome.

Perhaps a pic. ot two may be enlightening. (Groan.)

de

 

[aphetica]

I'm having an issue with the screen on my 520c, although I think it uses a different screen than the 540c.

Here is a pic.~

http://i63.photobucket.com/albums/h149/aphetica/520c_screen.jpg

I have a spare screen if it comes down to having to replace it, but I am really not looking forward to taking apart any more laptops.

Oh... and I have no idea why the hard drive is named "Sharique". It was like that when I got it and I can't figure out how to change it for some reason. :?:

 

[equill]

The 520c's display is a 'passive matrix' (FSTN: fast supertwist nematic), and the 540c's is an 'active matrix' (TFT: thin-film transistor), so not only the operation but also the appearance differs. You may have noticed the blurring behind the pointer as it moves across the screen. Some adjustment is provided in a Control Panel, but the 'submarining' cannot be abolished completely.

If I interpret your pic. and your concern correctly, the screen is darkening inwards from at least the Apple Menu corner. Is that so?

Changeing the name of a volume is not possible if the HDD is locked (in software or at disk level), or while the volume is being fileshared. If File Sharing is automatically invoked at startup (a prior owner [sharique?] may have set this to happen) you may be unaware that that is happening if there is no control strip to show you. If this is the case, you will need to disable sharing of the volume from File::Sharing before clicking on its name will change that panel so that it can be edited. If the volume is locked, you may be able to unlock it in the panel Get Info. (Command-i, while the volume's icon is highlighted). If the locking is at disk level a password may be necessary to undo it, or NUM may have been used and need to be used again for the unlocking.

de

 

[aphetica]

No, it was just dark because of the angle the pic was taken at. I'm talking about the yellow (orange maybe? I'm colorblind) line running vertically down the screen. It showed up randomly a few weeks ago and hasn't gone away since.

Thanks for letting me know about the sharing thing... I'll have to turn that off and try again.

 

[Flash!]

That's a line of dead (dying) pixels and it won't get any better

 

[aphetica]

That's a line of dead (dying) pixels and it won't get any better

Any idea what causes it?

Alot of my electronics have been having failures like this and I am thinking it could be the area I moved to last year... it's extremely humid here.

 

[tomlee59]

I've never seen a partial column fault on a passive display; indeed, until your post I would've lost a bar bet on its being possible (and I'm still dubious). But the short answer to your question is that it can be caused by a faulty column driver or associated connections.

 

[Flash!]

I'm not sure what causes it, column driver electronics seems feasable I guess. This happened to a 520c owned by a friend of mine, but there were a lot more lines on his one....until we swapped out the LCD.

 

[alk]

Here's a picture. 700 KB, so dailup users beware: http://www.ppcmla.com/images/540c_Display_Grid.jpg

My description doesn't match the picture (or maybe the camera's electronic eye doesn't see the same thing I do, or maybe I'm over sensitive to the issue). Anyway, there's a demonstration of what I'm seeing. The image doesn't look like what I expect an LCD to look like. Even 5300c machines - rough contemporaries - the LCD looks MUCH better.

Peace,

Drew

 

[Byrd]

It looks to me like one of the plastic lens/films sandwiched between the TFT panel + backlighting has somehow become a little skewed.

JB

 

[wally]

It looks to me like one of the plastic lens/films sandwiched between the TFT panel + backlighting has somehow become a little skewed.
JB

Byrd's idea sounds good to me. It's been a while since I took one apart but I think there is a thick semi clear plastic light spreader panel, a thin plastic diffuser sheet, a thin plastic polarizer, then the LCD guts, from back to front. That polarizer sheet needs to be at the correct angle relative to the front bonded polarizer in the LCD to get good extinction (blackness) at all points excluding where the pixel field voltage is playing with the twist of the LC material. Perhaps the plastic sandwich was put together with the polarizer slightly cocked, or even worse if mechanical keying does not prevent, in the correct layer order but reversed front to back so that any angular error is doubled. And it would be really bad if the diffuser and polarizer were order interchanged! If you decide to do some investigation, you can just view each individual sheet with polarized sunglasses on to see which one does the polarization function.

 

[alk]

Byrd's idea sounds good to me. It's been a while since I took one apart but I think there is a thick semi clear plastic light spreader panel, a thin plastic diffuser sheet, a thin plastic polarizer, then the LCD guts, from back to front. That polarizer sheet needs to be at the correct angle relative to the front bonded polarizer in the LCD to get good extinction (blackness) at all points excluding where the pixel field voltage is playing with the twist of the LC material.

That doesn't sound right to me. Two linear polarizers that aren't aligned correctly cause an apparent dimming of the light passing through them, they don't create a grid pattern. So if the polarizer behind the LCD were somehow out of alignment by rotation (not merely translated - that should have no effect), I would expect to see an overall dimming of the display brightness, not this grid pattern.

[...] or even worse if mechanical keying does not prevent, in the correct layer order but reversed front to back so that any angular error is doubled. And it would be really bad if the diffuser and polarizer were order interchanged!

I suppose that could be a possibility, but I don't understand how that would cause this crosshatching pattern. In that case, shouldn't the display appear to be washed out as too much (unpolarized) light is getting through?

Peace,

Drew

 

[alk]

Here is a much better picture. The first one had poor focus. This one should be much crisper and shows the effect more clearly.

Picture. About 1 MB.

Peace,

Drew

 

[tomlee59]

From that most recent pic, it almost looks as if you are missing every nth pixel, although it's still hard to tell. Could this be the case? If you look at hi-res pix, can you detect any artifacts that would be consistent with that idea?

 

[~tl]

From that most recent pic, it almost looks as if you are missing every nth pixel, although it's still hard to tell. Could this be the case? If you look at hi-res pix, can you detect any artifacts that would be consistent with that idea?

It looks more like a quarter of each pixel is missing...

 

[wally]

...That doesn't sound right to me. Two linear polarizers that aren't aligned correctly cause an apparent dimming of the light passing through them, they don't create a grid pattern. So if the polarizer behind the LCD were somehow out of alignment by rotation (not merely translated - that should have no effect), I would expect to see an overall dimming of the display brightness, not this grid pattern...

I suppose that could be a possibility, but I don't understand how that would cause this crosshatching pattern. In that case, shouldn't the display appear to be washed out as too much (unpolarized) light is getting through?...

Depends on whether the particular LCD uses a black masking matrix everywhere but over the pixels. If it does, only the pixels can light up, and a grid pattern around all good pixels is impossible, only pixels misbehaving in vertical and horizontal patterns surrounding apparent good pixels but uniformly across the entire screen.

If the LCD does not use an integral opaque optical mask, with the LC material only loosely controlled in polarization along the drive lines and TFTs something has to be done with the light leaking past the row and column lines. I am postulating that the light leaks are the source of the grid pattern if the polarizers do not do a certain job.

If the row and column lines have a low enough duty cycle compared to the sample and hold function at each pixel, the LC polarization everywhere but the pixel locations will have some average polarization rotational factor everwhere approximately the same, and this can be taken advantage of not by exactly crossed polarizers, but polarizers crossed enough that the residual leaked and rotated light past the row and column lines ends up exactly crossed with the front polarizer, establishing a nice black level everywhere, except in those pixel locations where a sampled and held potential rotates the LC material differently and opens the shutter some. I don't know that your LCD works on this principle, but it might.

 

[wally]

Please pardon my ignoring the pics and not commenting, the recent storm thru the SF bay area took out my Sunnyvale wireless ISP; zero WiFi beacon from the neighborhood lightpole antenna, so I am left sucking thru a dialup 28Kbps straw similar to funkytoad's situation [!] !]'>