Tunnel Vision On Monochrome Active Matrix Powerbooks

What model are you specifically talking about?

I was only aware of the PB 170 having this issue due to moisture contamination, bad seal on the LCD.

From searching the forum here, it appears people have encountered it on the 170, 180, Duo 280, 540, etc... It appears all the early monochrome active matrix monitors were impacted by it, but whether or when it happens to a given system seems to differ significantly.

All of them had the same symptoms, darkening at the four corners that tended to get worse the longer the affected system was used, and it persisted even after the display was turned off, but would eventually disappear if left alone long enough, with eventual deterioration to the point where it swallowed the entire screen. It seems to be a progressive and terminal condition once it appears.

I know in one of the threads someone has good pictures of what it looks like.

One can easily discount the backlight since that would have nothing to do with darkening after the system was turned off, and caps don't seem to be an issue, since that was ruled out in yet another thread on the topic. It seems to be some kind of defect in screen itself somehow.

Ah well that is the first I'v herd of that.

post the links to those posts if you ever come across them.

Here you go:

viewtopic.php?f=10&t=19829

viewtopic.php?f=10&t=17338

viewtopic.php?f=10&t=14421

viewtopic.php?f=3&t=5858

viewtopic.php?f=10&t=2555

In one post in this thread Bunsen mentions his impacted Duo 280:

viewtopic.php?f=10&t=11953

It is discussed here, mixed in with other things:

viewtopic.php?f=10&t=7408

You discussed it with regard to the 170 here, but it appears to impact all the other monochrome active-matrix models as well:

viewtopic.php?f=10&t=18921

Do you think it is the same moisture ingress as with the 170? Do the symptoms fit?

Ok great. Glad the Mac Portable doesn't have those issues.

Those consolidated threads in this one will be helpful.

Anyone have a vacuum pump that is large enough to accommodate a powerbook 170 LCD screen?

I would like to add. I have a powerbook 180, my screen had the same issue. I bought a screen from another member on this forum that was tested in his powerbook 180 for hours and the issue did not occur. I got the screen, didn't have a chance to install for 6 months. When I did swap the screen with mine, the new screen had the exact same issue.

This leads me to believe the problem is seperate from the screen itself, somewhere in the lower section of the laptop.

My thread:

http://68kmla.org/forums/viewtopic.php?f=4&t=21754

well that could be it or the seller told you a fib

Ok great. Glad the Mac Portable doesn't have those issues...

Click to expand...

I had the exact same thought when I was looking into this issue. The oldest one amongst all of them doesn't have the issue, yet all the subsequent monochrome/grayscale active matrix panels in the portable/powerbook family do. I wonder what the difference is?

I would like to add. I have a powerbook 180, my screen had the same issue. I bought a screen from another member on this forum that was tested in his powerbook 180 for hours and the issue did not occur. I got the screen, didn't have a chance to install for 6 months. When I did swap the screen with mine, the new screen had the exact same issue.
This leads me to believe the problem is seperate from the screen itself, somewhere in the lower section of the laptop.

My thread:

http://68kmla.org/forums/viewtopic.php?f=4&t=21754

Click to expand...

That is an interesting finding. That would be quite something if it turned out to be an issue with the circuity in the system rather than in the LCD itself. However, if it was in the system itself, wouldn't the other types of screen suffer from a similar fate? What makes the grayscale active matrix susceptible?

Really, the screen in the portable is quite beautiful

9.8" Active Matrix, it's easy to see why the system cost so much.

I'd love to have one to add to my collection, but as a result of age, and design issues, they seem to be more trouble than I would want to deal with. They belong with better collectors than I.

i know a guy that might sell you one. his name is hap.

just throw a battery in it... if you are worried about the battery going bad just keep it plugged in...

mcdermd keeps his plugged in full time.

If the root cause is not delamination reducing capacitance, then it has to be to do with attenuation of the signals, and so most likely caps related. Or possibly gradual decline in the conductance of the traces leading to the screen edge connections to each matrix line. I haven't seen inside one of those, but if the traces on the connecting cable fan out from the centre, the traces to the corners will be longer, and attentuation would be seen there first.

Just speculation...

Rick

Well because its only the active matrix, I am thinking the early transistors are going leaky on the internal plane. Either that, or LCD contamination due to bad edge seals. This fabrication process may have changed on the color displays so you dont see these faults.

All liquid crystals require AC drive, otherwise the pixels will supertwist and get stuck on, then fade.... Also when applied to DC, the liquid crystal begins to take on a di-electric property and hold a charge, and when the DC is removed it takes a bit for the charge to leak off. Which is what is happening. Also if the potential is high enough on DC it can actually damage the LC. This is why typically liquid crystals are driven with an AC signal.

im beginning to think its because the transistors are going leaky, so they are causing a DC bias on the AC signal. which is bad news for liquid-crystals.

DC can also cause electrolysis within the display, breaking down the conductive oxide electrodes.

The fact that this occurs on the edges does make me suspect that moisture has something to do with it. It isn't something I've seen before though, and I'm not sure why it would work ok for a while after being turned off.

As i said in another post, i baked my pb170 display for 20 min and it was about 20-30% better.. really, i'm not joking.

i do not have the laptop any more. if i did i would bake it even more...

again? what would a vacuum chamber do ?

Or a 5 gallon bucket of rice for a couple weeks?

Well, if the display I ordered develops this, testing will be done, and if the case appears to be terminal, I will be happy to send it to whoever things they have the best chance of being able to determine exactly what is causing it. Then at least we may be able to mount a defense against, or at the very least, develop a better understanding of the syndrome.

Well, I have a good vacuum pump, but the chamber is the difficult part. Suck the air out of something and you end up with intense pressure trying to crush it. I don't know how an LCD panel would behave in a vacuum though, it may leak/boil out the liquid crystal compound.

Well, considering we don't have much else to go on, it's worth a shot if all else fails.

i agree, i think this is worth investigating.

i always like knowing what the problem is.

Wonder if you bake it under a vacuum, kind of like a CRT, what would happen? hmmmm.....

I've had one with the bad tunneling. It was very bad when I first got it, it had been sitting in an unheated garage for quite some time (got it mid winter). I found it cleared up slightly after being in the house for a while. It wasn't completely fixed but it was not nearly as bad as when I first got it.

The other two I had did not have that issue. However, it seems over time one of them did develop tunneling(I sold the screen to Brooklyn).

Would be good to get to the bottom of the issue and figure out if there is a way to reverse it, or at least prevent it on ones that have yet to develop tunneling. Since it seems age is going to take out more and more of those screens.

Well, the screen I ordered has Tunnel Vision.

One thing I noticed on this screen, in the corners where the screen was turning "black", it wasn't losing the ability to display an image, but the polarity of the liquid crystals had inverted. When I moved my pointer into that area of the screen where it had darkened the color of the pointer inverted, but other than that it looked perfectly normal. When I moved the pointer into an area where that was unaffected by the darkening it went back to its typical color.

Does anyone know what could make the liquid crystals in the corners of the monitor invert their polarity like that?

Another bit of data for the mystery. I took the panel apart to see if I could find any physical defects. After removing the backlight, diffuser, etc... I was able to see through the panel and it was perfectly clear. I put it back together, put it in my powerbook and it looked great. After about 30 minutes the tunnel vision effect started to appear. I left it on for an hour after that to see how far it would progress. I the took the panel apart again and tried to see what it looked like now and I discovered something. Not only was the darkness at the corners and around the edges present, but the actual menu bar (which was extensively involved after an hour of darkening) was still present! I know it was the menu bar because I could easily read "File", "Special", Finder, etc... when I looked through the LCD. Somehow, whatever this is, can actually cause a complex image to be retained on the screen after power has been cut. So, does anyone know what could case a polarity inversion and allow a image to persist on a TFT-LCD after power is removed but eventually degrade to the point where the LCD looks completely normal, but have it come back again with use?

Because of crystal contamination, or a "charged" state of the Liquid crystal due to an un-wanted DC Bias. The liquid crystal is being driven with a large enough DC-offset most likely caused by leakage currents from either contamination/moisture, or failing TFT transistors in the substrate, this then causes the crystal to build a charge like a capacitor. And thats the effect you see.

Well, if heating helps, I'm inclined to believe it's moisture. I'm going to try baking the screen and see what happens

dont go too hot, itll melt the polarizing film on the panel. Youll need to heat it just under that softening/melting point and let it simmer for an hour or more.

I figure just above the boiling point of water should work. If that fails, I'll send it to James to shove in a vacuum.

In the name of science (and vintage computing)!

here is your answer from above from techknight:

Also when applied to DC, the liquid crystal begins to take on a di-electric property and hold a charge, and when the DC is removed it takes a bit for the charge to leak off. Which is what is happening.

Click to expand...