New theory on the cause of the infamous Tunnel Vision problem - Testers needed!

[Shaddam IV]

I have a PB 180 that showed relatively mild tunnel vision when I got it: Left side only, Apple symbol and lower left corner turned pretty dark, the left screen edge for maybe 15 px turned somewhat dark. I turned the metal prongs on the reverse side (where the screen was dark) and lifted the screen off the board a bit, keeping it up with tooth picks. The thought was that I wanted a gap between the board and the screen so that hot air could go between the screen and the board, and any water had a place to evaporate. I then placed the screen in the oven, about 70°C, 4 h. Now the left side shows only very mild darkening after 20 mins, only noticeable when you know what you're looking for. I may bake it again using the same method.
This is the first time that I saw baking have any effect. I tried a similar method (without lifting the screen off the board) with a PB 540 and another PB 180 screen - to no effect. I may try again. (Unfortunately the 540's power supply seems to have died, I'm no longer able to turn the machine on.)

 

[imactheknife]

I have a PB 180 that showed relatively mild tunnel vision when I got it: Left side only, Apple symbol and lower left corner turned pretty dark, the left screen edge for maybe 15 px turned somewhat dark. I turned the metal prongs on the reverse side (where the screen was dark) and lifted the screen off the board a bit, keeping it up with tooth picks. The thought was that I wanted a gap between the board and the screen so that hot air could go between the screen and the board, and any water had a place to evaporate. I then placed the screen in the oven, about 70°C, 4 h. Now the left side shows only very mild darkening after 20 mins, only noticeable when you know what you're looking for. I may bake it again using the same method.
This is the first time that I saw baking have any effect. I tried a similar method (without lifting the screen off the board) with a PB 540 and another PB 180 screen - to no effect. I may try again. (Unfortunately the 540's power supply seems to have died, I'm no longer able to turn the machine on.)

The pins inside the 540 may need to be bent back out. Also, the 540 psu definitely needs recapping as well. Just bought another 540c and its power supply reaked of fish smell

 

[ObeyDaleks]

Just doing some research... I did notice that almost in all pics I've seen where there's been improvement, the outermost edges are nearly perfect, while the areas inside the edges show only incremental improvement. Given that the going theory has to do with layer adhesion and trapped moisture, could it be that the edges re-adhere faster, thus trapping some moisture just inside the edges?

If that theory hold water, I wonder if it would be possible to heat the LCD from the center and work your way outwards. Say, with a heat gun and a thermo-couple to control the temperature.

 

[okto]

If that theory hold water

hehehe

 

[3lectr1cPPC]

Just doing some research... I did notice that almost in all pics I've seen where there's been improvement, the outermost edges are nearly perfect, while the areas inside the edges show only incremental improvement.

That’s why I thought mine regressed. See the photos of right after the oven, versus around a year later:



Note how the tunnel vision overall actually has improved further. But in the initial photo, the edges are perfect while now they’re tunneling. Not sure why that would be.

 

[ObeyDaleks]

I wonder if baking seals the edges initially (due to the metal bracket etc), trapping the remaining moisture, then later they come apart and allow some of the trapped stuff to escape out while it's diffusing between the layers. Hence the improvement over time. If that's the case, repeated bakes a few months apart might be much more effective than repeated bakes back-to-back. Of course, this is all complete conjecture.

 

[GRudolf94]

Given that the going theory has to do with layer adhesion and trapped moisture, could it be that the edges re-adhere faster, thus trapping some moisture just inside the edges?

No. It has nothing to do with adhesion. If the layers were to separate you'd have a permanently damaged display. They don't, can't and won't re-bond. This (probably) has to do with moisture dispersed in the liquid medium.

If that theory hold water, I wonder if it would be possible to heat the LCD from the center and work your way outwards. Say, with a heat gun and a thermo-couple to control the temperature.

Heat alone will do nothing - it is simply an aid to draw out moisture. Heating the center would probably cause other kinds of damage. It has to be uniform. A heatgun+thermocouple is a guaranteed method to cook a panel.