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TI-66 display issue
08-16-2019, 02:40 PM
Post: #1
TI-66 display issue
I am excited to have purchased a nice example of a TI-66 and the printer that goes with it for $60. The calculator powers on okay, but the display gives me a certain glitch.

Some segments turn on or off when they shouldn't. It's not really random, because if you key in a certain sequence, like 22222222 for example, you will tend to see the same sort of patterns repeat. It isn't a mechanical fault as near as I can tell. There are not only missing display segments. Sometimes it adds in segments that don't belong.

Then if you press the = key repeatedly sometimes the screen will work properly until you press = again.

I'm not really sure, but it seems that if I turn the calculator off for a little bit, and then turn it on and key in the digits really quick, it works fine. A few seconds into it, things misbehave. If I store a value in a register and then turn off the calculator, wait a few seconds and then turn it on the RCL the value it appears properly.

Any thoughts? Should I replace the batteries? Does it do any good to replace any of the discreet components on the board? I know that the toshiba chip is proprietary, but what about the other one?

Thanks for any ideas.

-Carl Gundel
http://www.libertybasic.com


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08-16-2019, 05:31 PM (This post was last modified: 08-16-2019 05:34 PM by jebem.)
Post: #2
RE: TI-66 display issue
It looks like a LCD issue.
If you are lucky, this can be a connection issue between the main board and the LCD assembly, and it should be easily to fix by cleaning the connection pads with some electronics contacts dry cleaner or just apply a drop of IPA.

Batteries can leak inside as well and corrosion may occur.
In this case deeper cleaning with some acid solution (I use kitchen vinegar) may help.

If the issue is the LCD itself, then applying hot air from a air drier for around 5 minutes may fix the missing segments.

Here some details on the inside.
https://www.hpmuseum.org/forum/thread-28...ight=Ti-66

Jose Mesquita
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08-16-2019, 06:03 PM
Post: #3
RE: TI-66 display issue
(08-16-2019 05:31 PM)jebem Wrote:  It looks like a LCD issue.
If you are lucky, this can be a connection issue between the main board and the LCD assembly, and it should be easily to fix by cleaning the connection pads with some electronics contacts dry cleaner or just apply a drop of IPA.

Batteries can leak inside as well and corrosion may occur.
In this case deeper cleaning with some acid solution (I use kitchen vinegar) may help.

If the issue is the LCD itself, then applying hot air from a air drier for around 5 minutes may fix the missing segments.

Here some details on the inside.
https://www.hpmuseum.org/forum/thread-28...ight=Ti-66

Thanks for the reply. I know the photo shows only some missing segments, but sometimes segments turn on which should not. In addition as I said in my original post, pressing = repeatedly will often flip the state of the segments and even cause the display to work correctly, and then not work correctly.

I will take your advice and have a look inside to see if there is any corrosion.

-Carl
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08-20-2019, 02:57 PM
Post: #4
RE: TI-66 display issue
(08-16-2019 06:03 PM)CarlGundel Wrote:  I will take your advice and have a look inside to see if there is any corrosion.

Seems completely spotless inside. No battery leaking ever as near as I can see. I will still try to clean the display contacts.

-Carl
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08-20-2019, 03:48 PM (This post was last modified: 08-20-2019 03:51 PM by jebem.)
Post: #5
RE: TI-66 display issue
(08-20-2019 02:57 PM)CarlGundel Wrote:  
(08-16-2019 06:03 PM)CarlGundel Wrote:  I will take your advice and have a look inside to see if there is any corrosion.

Seems completely spotless inside. No battery leaking ever as near as I can see. I will still try to clean the display contacts.

-Carl

Well, a fresh battery as you initially suggested is worth the try, despite a weak battery should not result in such strange behavior.

Assuming that the battery is good, I see three common causes for strange behaviors:
1. Battery electrolytes leaked over the mainboard;
2. Electrical conductive liquids (like coca-cola or similar) dropped over the keyboard may have found their way to the mainboard;
3. Faulty SoC (System on a Chip processor.

We can fix causes #1 and #2, by fully dismantling the machine and cleaning it all (except the LCD assembly) with warm water and dish hand wash detergent, and before it drys, use IPA (isopropilic alcool) on the mainboard to remove the water and remaining residues, then let it dry under warm room temperature for one day. The LCD can be cleaned with IPA alone.

As for cause #3, a new SoC chip would be required and as far as I know can only the found on a donor machine these days.

While battery leaking is not common on coin cells, it may indeed leak and I found quite a few calculators with corroded and short circuit PCB traces by the battery electrolytes.

Jose Mesquita
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