Tunnel Vision On Monochrome Active Matrix Powerbooks

[mg.man]

Just chiming in... Glad I found this thread!...  I recently purchased a faulty (screen issues) PB180, figuring it probably needed a re-cap (which I've done on my PB100 with success...  Oh no... it had a serious case of tunnelling...  Just like @GregorHouse mentioned originally "Corners begin to dark after a few seconds and in a two minutes nearly all of the screen is dark."  I was about to go on the hunt for a new display... when I found this thread and realised I was not alone.  So... I stripped the display, pulled the panel and baked it yesterday for ~4 hours @ 90C (I'm in the UK)...   The results were encouraging... but the tunnelling started to re-appear after about 10 - 15 minutes.  Nowhere near as bad as before... but still there.  I'm currently in the middle of my 2nd 'bake'... and will report back when it's done, cooled and re-instated...   Thanks to all for the contributions to this thread!... 

 

[GregorHouse]

Hope it works, let us know  

 

[techknight]

Serious cases would probably need lots of desiccant and serious baking time. 

 

[mg.man]

Serious cases would probably need lots of desiccant and serious baking time.

Sounds like you've been there before....  ;-)

Update on mine... baking Round 2 was 4 hours @ 100C.... I bumped the temp slightly since 100C is the boiling point for water (212F)...  

Initial results were even better than Round 1... here we are right after full boot...



Unfotunately, after ~2 minutes... the darkening started... 



...and after ~11 minutes... it was starting to really show... 



I still consider this a positive result... before any baking, the screen started to darken almost immediately, and after 10 minutes - the corners were totally black and only about 50% of the viewable area could be seen.  So this is a VAST improvement and I believe fairly positive evidence that the issue is moisture.  I've put the PB to one side for the moment... other projects call, but my plan is to do a serious Round 3 bake - probably for 8 hours or so... I may or may not bump the temp up another 10C...  I welcome any comments / feedback.... 

 

[techknight]

yea, you gotta keep going. 

But careful turning up the temperatures! you dont want to create vinegar syndrome on the LCD polerizing film. 

 

[mg.man]

But careful turning up the temperatures!

So stick with 90C?  ... just bake longer?

you dont want to create vinegar syndrome

Um... can you explain?  

 

[mg.man]

can you explain?  

...found this   

 

[GregorHouse]

Yes, be careful not to go too high, you don’t want quick expansing gasses inside the screen that may crack it. Also vinegar could appear. Bake for longer and if you have it add some dissecant, like silica bags or similar

 

[Challenger 1983]

I’m thinking of buying a PowerBook duo with bad tunnel vision, maybe I’ll try restoring it with this method, has anyone had good lasting results with this?

 

[techknight]

Mine was ok after it, but it did ruin the polerizing film eventually from too much baking so I retired it. I didnt have any dessicant packs to try that method. 

 

[Challenger 1983]

I wonder if maybe the act of baking it is introducing condensation as it cools back down, my thinking is that warm air holds more moisture than cold air, meaning the act of baking it will dissipate the moisture until it has completely cooled, at which point the moisture condenses and ruins the image. I think someone mentioned a food dryer as a possible method of removing the moisture, I would like to see that 

 

[rplacd]

I think someone mentioned a food dryer as a possible method of removing the moisture, I would like to see that 

Hmm, I'm thinking about alternatives as well: I live in a really humid climate, and I'm wary of using an oven. I wonder if simply putting the screen in an airtight container with a really good desiccant, like a molecular sieve, could work, leaving in the screen as long as possible, repeating as many times as required. Apparently these are used to extract water from ethanol!

 

[cheesestraws]

like a molecular sieve, could work

 I've always understood that molecular sieves are a bit more specific, and may not help removing water from air; they rely on the thing they're trying to remove having a very different size of molecule from the thing it's removing it from, which is why they're good at removing water from organic solvents.  My guess is that you'd be better off with something like calcium chloride, but that is only a guess.

 

[rplacd]

 I've always understood that molecular sieves are a bit more specific, and may not help removing water from air; they rely on the thing they're trying to remove having a very different size of molecule from the thing it's removing it from, which is why they're good at removing water from organic solvents.  My guess is that you'd be better off with something like calcium chloride, but that is only a guess.

Ooh, that's a good idea! Maybe cover the whole thing in calcium chloride, like mummifying a corpse. Same process eh?

 

[demik]

Hello,

Just tried this ona PB180 screen with severe tunnel vision. Here is the screen after 15 min of use :

I baked the screen for 6 hours @ 100°C (212 °F), and the result is better, but not perfect.

Here it is after baking and two hours of use :

I will leave this as it for now, as the hinge broke during reassembly.

 

[beachycove]

One of the things that interests me about this thread and the baking of PowerBook screens (!) is that it pretty much confirms the moisture theory surrounding tunnel syndrome. So here’s a question: has anyone witnessed tunnel syndrome on a machine that has been kept in a desert environment, e.g., in the SW USA or the like? 

I once scrapped a Duo 280 (greyscale) because of the screen problem. I am regretting it now.

 

[demik]

One of the things that interests me about this thread and the baking of PowerBook screens (!) is that it pretty much confirms the moisture theory surrounding tunnel syndrome. So here’s a question: has anyone witnessed tunnel syndrome on a machine that has been kept in a desert environment, e.g., in the SW USA or the like? 

I once scrapped a Duo 280 (greyscale) because of the screen problem. I am regretting it now.

I have another PB180 and a PB170 without any tunnel syndrome, so maybe. The PB180 was kept inside a bedroom for the past 12+ years (Europe)

 

[micheledipaola]

I have bought a PB Duo 280 which is showing tunnel vision, I am a bit reluctant to bake the screen, so I would maybe try inserting silica bags before or something similar. Anyway I will let you know - thanks for all the hints here!

 

[rplacd]

I have bought a PB Duo 280 which is showing tunnel vision, I am a bit reluctant to bake the screen, so I would maybe try inserting silica bags before or something similar. Anyway I will let you know - thanks for all the hints here!

I'm not too optimistic about using silica bags. I tried storing a PB180 screen with about 2 pounds' worth of calcium chloride dessicant pellets; after a month, the screen tunnels at the same rate.

 

[pbertolo]

My experience. PB 170 with severe tunnel vision issue, after a few minutes most of the screen was unreadable. 

Vacuum bagged it (with vacuum cleaner, not pump, not be too harsh) with some moisture absorber (plus spacers for avoiding crushing the plastics). For a long, long time (2 yrs ago). Now it can run for some reasonable time (2 hr) before the darkening appears. Still, at a much lower extent compared to original conditions. 

Curious thing: switch the unit off and next day darkening is gone and you can still count on a couple of hours of decent use (assuming you need it!).

So, I would conclude humidity is indeed a factor, but probably not the only one.