Hi,

I recently bought a second hand TI-81 graphical calculator. When I turn it on and press on the screen appears completely dark. I've tried lowering the contrast by pressing 2nd->down repeatedly but that didn't help, and I removed the lithium battery to clear the internal memory, however it still occurs.

Another thing I noticed is that I can't turn it off. If I press 2nd->On (off), the screen stays dark and does not clear.

There is a little battery leakage around 2 of the springs in the battery compartment but nothing that major. I was using fresh AAA batteries when testing it.

Any help would be appreciated.

Welcome to Cemetech. Usually there is an issue with dead areas on the screen which is caused by the internal ribbon connector developing a dry bond with the screen PCB. However it sounds like your screen is healthy in that respect. Try this link to a similar thread:
[url]:
http://www.cemetech.net/projects/uti/viewtopic.php?t=1198&start=0


The self-test option noted in the link may resolve the issue and this would be the best course of action before attempting to open the case.

Let us know how you get on. Also, feel free to introduce yourself in the apprpriate forum.

I did the Clear + On test while inserting the batteries but that didn't change anything. I was a bit worried to do the full self test, that other thread said it entirely cleared the memory including the OS? I don't have a copy of the OS or a way of connecting the calculator to a PC.

I have done the self test on most of my calculators with no ill effects.
The 81 does not have a flash memory and even if it did it should not clear the OS. It will probably clear down variables but as you have not used it yet it won't matter.

If the black screen persists one of our senior members may be able to help. As there is no link port there is no way it has been "bricked" by a faulty hack.

Entering the self-test on the TI-81 is done by turning the calculator on (might want to manually turn it off and back on again to make sure it's at the Home Screen so the key sequence will work) and pressing and releasing the keys [2nd], [MATH], [ALPHA], [LN], [ENTER] in that order. It won't clear the OS, just programs, statistics data, and variables—in other words, only user-entered data is erased.

I don't recall the exact self-test sequence on the 81. It's slightly different from the 82/85/86. It probably involves pressing keys several times to advance through the LCD test patterns and contrast steps, and if there's a keyboard test, pressing the keys in left-to-right, top-to-bottom order. Maybe an [ON] press or two in there somewhere. Eventually it would end with a "Mem cleared" on the screen if the LCD works.

Thanks for all your help. I tried the self test, however the screen is still black. The display did not change during the test so I do not know if it completed successfully or not. I have tried changing the batteries between tests and doing it with and without the lithium battery, but I get the same result every time.

I think it's pretty clear therefore that you have LCD ribbon cable failure. Do you have any soldering experience? This topic talks about the problem and how to fix it:
http://www.cemetech.net/forum/viewtopic.php?t=5161

I opened up the calculator and checked the ribbon cable with a multimeter. I tested to see if I could get a connection from the pad on one side of the cable to the other, and I could get an electrical connection through all the wires in the ribbon.

I did notice there was a fair bit of corrosion to the silver cover, and there was some corrosion around the battery terminals. Could this have anything to do with it?

A connection is one thing; low and consistent resistance is another thing. If it's like 4 ohm, 4 ohms, 6 ohms, 50 ohms, the signals to the LCD will probably be distorted. I usually replace anything above about 30 ohms. But yes, the battery acid corrosion could absolutely be part of the problem.

I tested the connections on the ribbon cable again and all of them had a resistance of 1.4 ohms. So do you think the battery acid is the problem, and if so is it fixable or should I look for a replacement calculator?

Thanks for posting the images. Kerm is absolutely right, ofcourse : an electrical connection is insufficient - the Ohmic values are key particularly in data transfer. Also looking at that sheild, it's clear there is a corrosive agent in there. If the batteries were left in place whilst degrading, you have a great environment in which to give rise to all sorts of problems whilst the cells are "gassing".

I think you are looking at a bit of soldering there. Kerm posted some images a while ago of his project but it's not for the faint hearted. Good luck !



Unless you want to do some surgery and possibly still not cure the problem you may want to consider a replacement. It depends on your motives for having an '81 in your collection...

Yes, I think the battery acid is the problem. You could probe around for traces that got corroded past usefulness and try to jump around the breaks, but you might just be better off trying to get another one. TI-81s tend to be very cheap on eBay and similar places.