Texas TI-66 Programmable: Toshiba skills to rescue Texas...

[Csaba Tizedes]

Hi,

I have a TI-65 in a very good shape and working condition, but on the LCD some annunciators and the segments of exponent display don't lit. And few weeks ago the keypad second row from the bottom (RST/BST/SST/X<>Y/SUM+/1/2/3/-) stops functioning.

Have you got any idea it is easily reparable?

How to dismantle this unit? ("To open the case it is enough to remove one single screw from the back cover." - is it same for TI-65? Where is that screw?)

Thank you!
Csaba

[grsbanks]

(12-17-2017 02:45 AM)rprosperi Wrote:  I don't collect too many TI machines, but this is one of the ones I do have. These landscape machines 65, 66, 67 are nice (but slow!). I can send it so you can compare with a working unit if that will help, assuming the RAM doesn't fix it. Holler if you need it.

Thanks for the offer, Bob. Much appreciated.

I've not actually taken an oscilloscope to the machine yet but the corroded bits are clearly the first things to sort out.

I found a new RAM chip from a seller in London and I'll probably have it in the New Year.

[grsbanks]

(12-17-2017 08:29 AM)Csaba Tizedes Wrote:  I have a TI-65 in a very good shape and working condition, but on the LCD some annunciators and the segments of exponent display don't lit. And few weeks ago the keypad second row from the bottom (RST/BST/SST/X<>Y/SUM+/1/2/3/-) stops functioning.

Have you got any idea it is easily reparable?

The TI-65 is a machine that I don't know at all. Actually, its architecture is completely different from the TI-66. For one thing, it's a TI device (as in made by TI) with a flexi-PCB and a couple of TI processors that work in a master-slave configuration. I'm guessing one of the CPUs manages the display and the keypad while the other does the actual calculations. The TI-66 is Toshiba-made.

Does the display blank when you press a key? If so, that's usually a reasonable indication that the same CPU is handling both.

It could be corrosion. That was pretty common for those machines that ran on a pair of LR44 button cells. If so then you might be in time to fix things given that the problems only started recently.

Looking at a picture of the machine's innards (see http://www.datamath.org/Sci/Galaxy/TI-65.htm), I don't see a screwhole so I suspect the case is held together purely with clips. In fact TI seem to have gone down the screwless route with this calculator as I see that the LCD is held on with heat-stakes, making dismantling that part extremely unadviseable.

Not an easy one here!

[HrastProgrammer]

It would be great if the ROM could be dumped from this calculator ...

[psychlist]

OK, so some time later...the failure of my more modern calculator prompted me to up my game and start using my old TI-66. The LCD display transparent acrylic? cover was foggy/scratched from abrasion, so I flippantly dismantled it. I tried T-Cut Original (car scratch repair cream from my Dad's garage and probably 30 years old), and it removed 90% of the fog/scratches. But something bothers me.

The attached photo shows how I think the "rubber" strip was during dismantling. IIRC it didn't fall off due to stiction or something. The position was very similar to that in OP's own photos. But I can't understand how it can be there functionally. Surely it separates the contacts on the main board with contacts on the display board. But if I keep it there it, the calculator does work. It also feels like I have to press the display module down a bit hard to engage the grey retainers left and right.

Why does it work?



   

[psychlist]

(01-11-2015 06:49 PM)jebem Wrote:  This time I have lost one of the two tiny small springs shown in the initial photo of my OP, when trying to put it back into the power On key.
The damn thing just jumped in front of me and I'm afraid it's gone for good.
After spending 1 hour looking around I have quit my search and have just assembled the unit without it.
Apparently it works fine. But I know it is missing, and this will bug me for a while.

Whilst dismantling, I didn't see springs. Then I found one on the floor. I couldn't see how it could go back in the "on" key. I noticed a second spring which I assume never fell out during dismantling. In the attached photo you can see it in the far bottom right hole that is used for screwing the main board to this front case. I noticed that the matching hole on the main circuit board had metal contact at the top unlike all others bar one. I made a guess that it was something to do with grounding (noting Mark Hardman's post). The other screw hole on the main board with metal contact on the top was the one matching the far bottom left screw hole on the front case (i.e. far bottom left in the attached photo). So I put the found spring in there.    

[brouhaha]

(12-04-2023 09:59 AM)psychlist Wrote:  Surely it separates the contacts on the main board with contacts on the display board. But if I keep it there it, the calculator does work. It also feels like I have to press the display module down a bit hard to engage the grey retainers left and right.

I can't really make out much in your photo, but from your description, I can tell you what it is. It's not there so much to separate the contacts as to connect them. It's an elastomeric connector. These were very commonly used with LCDs in the 1970s and 1980s, but have since been mostly replaced by an FPC or FFC flex cable attached to the PCB by adhesive and soldered with a hot bar.

[brouhaha]

(12-18-2017 09:14 AM)HrastProgrammer Wrote:  It would be great if the ROM could be dumped from this calculator ...

...and if we knew anything about the processor architecture. Maybe it matches one of the TI CMOS calculator processor architectures, and maybe not.

The package appears to match the TMP47C22F of the Toshiba TLCS47C family of 4-bit microcontrollers, but the pinout does not. The LCD drive of the part is comparable to the TI-66 requirements. It has 2Kx8 ROM and 192x4 bits of RAM. Doesn't seem like enough ROM. There were later versions with 4Kx8 ROM and 256x4 RAM, but the match the pinout of the C22F, and not that of the T6875A.

If it's a Toshiba architecture, it probably matches the TLCS47C.

[psychlist]

(12-05-2023 10:06 AM)brouhaha Wrote:  

(12-04-2023 09:59 AM)psychlist Wrote:  Surely it separates the contacts on the main board with contacts on the display board. But if I keep it there it, the calculator does work. It also feels like I have to press the display module down a bit hard to engage the grey retainers left and right.

I can't really make out much in your photo, but from your description, I can tell you what it is. It's not there so much to separate the contacts as to connect them. It's an elastomeric connector. These were very commonly used with LCDs in the 1970s and 1980s, but have since been mostly replaced by an FPC or FFC flex cable attached to the PCB by adhesive and soldered with a hot bar.

Yes, sorry, I couldn't seem to get a decent photo. Many thanks for letting me know about elastomeric connectors. It kind of of had to have that functionality but I'd never heard of them. I can see the appeal but it is tricky to align without a retainer. I'm quite enjoying using the TI-66 with a lovely clear display.

[Pierre]

I just read this topic with interest but also very surprised.
I own a TI-66 and its printer and this calculator has been a big disappointment for me.
Indeed, a former follower and fan of TI-58C, I expected to find a worthy successor to the old TI... but apart from the alphanumeric display of instructions...
no plug-in modules, and no more "cheating" possible.
The hidden HIR function had however gained many followers.
For slowness, simply turn the 2 “6”s a quarter turn to the left to imagine 2 snails racing.
Above all, I would have liked the expected marketing of the TI-88 but unfortunately...
So I made up for it with the HP-41 (c/cv/cx) and some peripherals !
(despite my collection of TI calculators)