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Tunnel Vision On Monochrome Active Matrix Powerbooks

Paralel

Well-known member
Further investigation reveals that the screen is not dead! The polarizing film on each side was severely discolored/burned, but the liquid crystals and the electronics are still completely functional!

Since it still sorta works, I'm attempting to see if the baking was successful.

Also, it appears the screen can be saved, I just need to replace the polarizing film on each side... Does anyone know if that is even possible?

 

Paralel

Well-known member
After running it for over an hour, I can confirm that baking the LCD does indeed work to treat (although hopefully it is a functional cure) what I like to call "The Creeping Black Plague"! Before if I had run it for 15 minutes The Plague appeared.

However, at the temp I used, 350 F, the polarizing film on each side of the screen was destroyed, although the actual liquid crystal and the electronics were intact. So, a lower temp of 220 is recommended (as was actually written above, which I completely misread, because I am apparently blind).

It looks like moisture contamination is indeed our culprit and it can be reversed!

 

Paralel

Well-known member
I'm too embarrassed given how it turned out as a result of the the temp I used being too high. It's a horrifying sight. 8-o

I am working on acquiring another 540, if that one needs to be baked, I will indeed use the correct temp and post before/after pictures

 

uniserver

Well-known member
Let's re-think the temperature before you bake the second screen.

I'm not sure what the polarizing film is made from but here is common plastic film characteristics:

http://en.wikipedia.org/wiki/Polyethylene

Polyethylene is a thermoplastic polymer consisting of long hydrocarbon chains. Depending on the crystallinity and molecular weight, a melting point and glass transition may or may not be observable. The temperature at which these occur varies strongly with the type of polyethylene. For common commercial grades of medium- and high-density polyethylene the melting point is typically in the range 120 to 130 °C (248 to 266 °F). The melting point for average, commercial, low-density polyethylene is typically 105 to 115 °C (221 to 239 °F).
What is the lowest setting of your oven?

There might be some differences between the powerbook 170 screen and the 540.

The screen does go all black(when baking), I do remember that when I baked mine.

 

Gorgonops

Moderator
Staff member
The "warm" settings on most ovens is usually somewhere between 160 to 200 degrees. (Which is, what, 70-ish to 95-ish C?) If the goal is to drive out moisture that's probably sufficient. (Just might take more time than a higher setting.) Damage to plastics aside it would seem to me that if the problem is actually water contamination the last thing you'd want to do is *boil* water that's trapped inside a glass sandwich. That sounds like a perfect recipe for cracking things. (Possibly on a microscopic scale.)

 

Paralel

Well-known member
I can tell you that the plastic turned a very deep amber color at 350, like a deep beer bottle brown with a prominent red hue to it. IDK if that helps us identify the plastic.

I think you are right about the screen itself cracking. After looking at it very closely, I noticed a 1/2 dollar sized region in the perfect center of the screen that had cracked. The crack(s) weren't visible, so it may have been a very fine crack, or a series of very small cracks, but either way, the liquid crystal escaped from that area.

Ah, see, I figured you'd need to boil the water out. Guess not...

Okay. If the next one is contaminated as well, we will try a lower temp, for a longer period of time. Something in the 180-190 region with examination every 15 minutes for at least an hour or two, longer if the screen doesn't appear to become perverted in any way.

If anyone else has any screens that are terminal, feel free to contribute to our process here as we work to hammer out the exact temp and duration necessary to fix this problem without damage to the screen itself. If you don't want to try it, I'm happy to accept screens and do it, in the name of science!

I have no idea what the lowest setting is, I'll have to check, I've never used it that low.

Another bit of info, at least at the higher temperature, it STINKS! I had to turn my exhaust fan on. It smelled like overcooked adhesive and plastic (no surprise, really)

 
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uniserver

Well-known member
here is some other basic info regarding LCD and temperature ranges.

LCD Family Item Celsius Fahrenheit

Standard STN Operating Range 0 to 50/60 32 to 122/140

Standard STN Storage Range -20 to 60 -4 to 140

Standard TFT Operating Range -10 to 70 14 to 158

Standard TFT Storage Range -20/-30 to 80 -4/-22 to 140

Wide Temp STN Operating Range -20 to 70 -4 to 158

Wide Temp STN Storage Range -25 to 75 -13 to 167

http://americas.kyocera.com/kicc/lcd/notes/tempconsider.html

 

Paralel

Well-known member
Excellent find, Uni, although their temp conversions are retarded. 80 C is ~175 F, not 140.

Going based on that, we can probably safely take it to 175 without any risk.

My oven goes down to 170, so that will be our next test. 170, with checks every 15 minutes until the screen either gets perverted, or we get to 3-4 hours, whichever comes first.

 

uniserver

Well-known member
got it… ok we get a 5 gallon bucket with a rubber sealing lid.

Fill it with rice, Then drill and tap a fitting into the lid and let (the LCD display) sit in a slight vacuum for X amount of time?

 

Paralel

Well-known member
Is rice really hygroscopic enough to pull out such a small amount of water from a screen?

We might need something with more desiccating power than that.

But I agree, we are better off trying this first than another heat experiment. This fails, no harm. Baking fails again, we have another dead screen.

I need to bring my Classic II (and now my Plus) to you to have them recapped anyway, so I'll just hand off the screen to you if this one is contaminated as well.

 

uniserver

Well-known member
Can you scrape both sides of the LCD with a flat razor blade, getting that melted film off? Then just maybe get a nice clean sheet of paper and place it behind the LCD?

might look pretty decent?

 

Paralel

Well-known member
It actually has polarizing film on both sides of the liquid crystal plane. I tried removing a section of the polarizing film on just one side, no dice, nothing could be seen. I put the piece of film back, and the image in that area reappeared. I tried removing a section of the film front and back and still nothing. Apparently this type of LCD relies on a polarizing film both front & back in order to display an image.

Both films were definitely polarizing. If I held them up to my eye and rotated it in front of my LCD TV, the picture would either be present or disappear as a result of the rotation of the film.

I would actually try replacing the film if it wasn't for the fact that the liquid crystal panel was actually cracked in the center.

 

techknight

Well-known member
You can purchase polerizing film. I forget what sites, but they are out there. They sell them in ether rolls or sheets. They do this so you can replace totally /scratched film on regular color LCDs.

 
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James1095

Well-known member
I decided to go full blast, 2 hours @ 350 F. I removed everything from the screen except for the actual liquid crystal panel itself and the attached control circuitry which cannot be removed. I shielded the control circuitry from the heat using a triple layer of tin foil (operating on the same theory as tin foil masking for a heat gun).
Holy crap! 350F is *WAY* too hot! When you bake out parts that have been exposed to moisture prior to reflow soldering, it's normally a few hours at just over 100C, or around 212F. Any hotter than that and you'll be wrecking things. Not to mention plastic outgasses all kinds of nasty substances when you get it that hot.

 

Bunsen

Admin-Witchfinder-General
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.
That seems like it might be a problem with the polarizing films, not the liquid crystal layer.

Might.

 
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