I have the normal Ti-89. When I turn on the calculator, the screen is half black. If I change the contrast, it does not help me see anything anymore. I used to be able to read the calculator by adjusting the contrast to barely make out the numbers on both sides, but now that doesn't even work for me.
Hey, i have nearly the same problem and now finally found a solution to it.
In my case half of the screen was empty and the other worked correctly AND slight pressure to the frame surrounding the display on the side of the defect half and/or above the display makes the display reappearing again. Because it's annoying if you always have to press with one hand on your calculator while working with it i did the following:
Important: Make sure that...
... you have a backup of the data stored on your TI because you could lose them during the following procedure.
... we are really talking about the same problem.
... this hints come without any warranty and you might destroy your calculator completely following this advice.
1. Open your TI 89 as described for example in 
2. Take a piece of foam rubber and cut out a stripe with a shape like |_ or "L", about 1cm in width which fits approximately the frame around the display on the the defect side and the top.
3. Place the foam rubber on the silver shield you see after opening the back of your TI.
4. Then you can assemble your calculator again.
I hope i could help you!
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The most likely answer is that the screen has partly failed.
Another user said 'The TI-8X series of calculators work great as standalone calculators, ... I've purchased at least 3 TI-8x's over the years and all of them died (screen failure)'
I've never seen a calculator with display clarity problems.
The only option I could think to offer you is to attempt to adjust the contrast. However, I'm not sure whether or not your TI-89 actually has an option to change the contrast. Because I own a TI-89 Titanium - and although its a wonderful calculator - it does not allow the user to alter the darkness/brightness of the display.
Call Texas Instruments: 1-800-TI- CARES...They are pretty helpful with common questions like this.
hit the diamond key and then the minus key. this shoud decrease the contrast. keep reapeating these same steps until your home screen is visible. hitting the diamond key, then the plus key turns up the contrast.
The ribbon cable that controls the screen is damaged (or the liquid crystal has baked out... tis happens when the unit is exposed to high temps or long periods of direct sunlight). From my experience w/ these calculators they cannot be repaired.