I am having trouble with the display on my TI-86: Rows of pixels come and go daily.
On some days, all rows are fully functional and on others, as many as 12 rows stop working.

Sometimes going into the mode menu and cycling the contrast between the lowest and highest will bring the rows back to functionality, but most of the time it doesn't bring all of them back. When I run the self-test by pressing 2nd-MODE-ALPHA-S on the calculator and get to the part where it turns all pixels black, the rows disappear and look to be functional. As the screen lightens up, the rows are still out.

I would like to know how I can fix this issue. I have opened up the calculator and have tested the continuity of the white flex cable connecting the motherboard to the display driver and all appears well. (I am not sure if differing resistances from data line to data line on this cable can be causing the issue.)

There is a black ribbon cable that is difficult to investigate since the ends of it are sandwiched between the LCD glass and the display driver's board. I have tried manipulating both cables while the calculator is powered to see if the display functions correctly to limited success. Sometimes manipulating the black cable will cause a different row to go out and come back in, but no matter how hard I try, I cannot get the rows that were initially causing problems to work. Sometimes just letting the calculator sit will cause rows to come and go, even the stubborn rows.

I plan on replacing the white flex cable with 30AWG wire to see if anything changes, but I believe it to be impossible for me to replace the black ribbon cable.

TL;DR
I believe my issue is caused by the flex cables (especially the black one), but running the self-test will always cause the dead rows to appear to be working when the test turns all pixels black.
Does anyone know of this behavior on other calculators (rows appearing somewhat functional during the black screen portion of a self test or when menu text is on the same row)?
Any advice on how I should attempt to fix my issue?
Hi there, it does indeed sound like a flex cable issue. Such issues are reasonably common on older calcs. I've had the same symptoms on my 83.

Kerm has done loads of LCD repairs, he might be able to assist.

Usually you can just resolder the ribbon in place however.
tr1p1ea wrote:
Hi there, it does indeed sound like a flex cable issue. Such issues are reasonably common on older calcs. I've had the same symptoms on my 83.

Kerm has done loads of LCD repairs, he might be able to assist.

Usually you can just resolder the ribbon in place however.


Thank you tr1p1ea, I completely replaced the white flex cable connecting the motherboard to the display's board using 30AWG and 22AWG wires, but the issue still wasn't fixed. I am almost certain that the issue is with the black ribbon cable that connects the display board to the LCD. The connections on this cable would be very difficult to replace with wire since the pads are so small and the ends of the ribbon cable are separated by about 1/8 of an inch in-between the glass and the board. I tried pressing the black cable's connections down with a toothpick to see if anything changed and one row of pixels became functional again, but the other would not become functional.

At this point, only one row of pixels are not functioning. I put in new batteries and ran the self test a few times and tried changing the contrast from highest to lowest and back on the mode menu, but the row still wouldn't return.

I then went into the graph format menu where the options covered more of the row that wasn't operating properly and began to cycle the contrast from low to high. The dead row actually came back! I do not know how long it will last since this is the third time all pixels have been working, however rows would then stop working after about a day. This is however, the fastest that particular row has come back from the dead by cycling the contrast.

TL;DR
I replaced the white flex cable with wire, but the issue still wasn't fixed. This told me that the issue was almost certainly caused by the black cable, which is much harder to fix. I then cycled the contrast on the graph format menu where the text covers most of the dead row, and that row came back. I don't know how long this will last since this isn't the first time that the rows came back only to die a day later.
Nice work on replacing the cable - sucks that it wasn't the issue.

Indeed the black ribbon would seem quite impossible to repair.

There is the possibility of doing an LCD transplant from a different calc - preferably one that isn't working for a different reason. What would your thoughts be on that?

EDIT - Heres one for 3 bucks! https://www.ebay.com/itm/Texas-Instruments-TI-86-Graphing-Calculator-Non-working-Parts/323820310948?epid=54842635&hash=item4b6531d1a4:g:TCwAAOSwPA1cScZ3

Corrosion in the battery compartment, not citing any LCD issues.

You might even just be able to clean the PCB etc to get it working for a cheap calc?
Thank you tr1p1ea again for your response.

I have it working better now and all pixels appear functional except three rows are very slightly lighter when the there is a blinking cursor on top of them. Those rows are also lighter during the self-test function. During normal calculations and graphing, the screen is fully functional and has high contrast.

I got it working by messing around with the black ribbon cable and pulling it taut, then taping it in place with some Scotch tape. After this, only one row of pixels wasn't working at all until I cycled the contrast on the menu until it worked.

As I'm writing, the LCD is working, but I don't know if this is only temporary. It has lasted one consecutive week without issue so far.

Thank you researching broken TI-86's that are for parts. I don't think I will buy a broken one even for $3 since I got this one for under 75 at Goodwill!
Unfortunately, we still haven't worked out a reliable way to fix the fine-pitched ribbon cable. The conductive glue holding it onto the glass of the LCD dries out; notipa in particular has spent futile effort trying repairs involving heat and pressure. One of our most promising avenues is just new LCDs with a controller that emulate the functionality of the originals, but soon we're going to run into the Flash/EEPROM chips on these calculators starting to degrade, or possibly even the ASICs themselves degrading. I have quite a few concerns about the long-term "archivability" of our dear calculators.
  
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