TI-59 LED intensity

Quick question: anyone know how to adjust the brightness of a TI-59's LED's? I have a couple of them with dim displays.

I just bought another cheap 59. I was considering it for "drop testing" until I saw that another one sold for $175!!!



Operate it with 4.5V instead of 3.6V...



Thanks, Joerg! Actually, I run them all at 4.5+ volts (lithium celled packs), but this one is still mounted to the PC-100C it came on today in the mail. I'll try it at home with lithium cells. It needs its card reader rebuilt also. The good news: I've never seen corrosion in the units that were left on printers. That's always nice. This one I got today, for $25, with keys in printer, had no battery pack stuck in the printer, and the contacts there are in perfect shape. Another nice find....

O.K. Any OTHER way to adjust LED brightness?


Hi, Doc; are you well?

By inspecting Spike de Wal´s TI59 diagram, one finds out that the battery voltage, indicated as -3.7V, directly feeds the two SN27882 (pin #1), the two IC´s closer to the LED display and responsible for its multiplexing control signal (select which digit). Each segment (SA, SB, SC, etc.) is 'lit' by the TMC0501, which is fed by Vgg (-15.7Vcc, pin #27) and Vdd (-10Vcc, pin #26). Because the voltage from the TMC 0501 that lits each segment is more negative than the voltage in the SN27882, they must be common anode.

In order to increase the brightness in such multiplexing display, either you increase the current across the load (the LED´s) or change the cyclic ratio. The second option means to redesign the circuit, and the first one may harm the LED´s. In any way, the output voltage from the (small) power board might be checked for the values presented here. Chances are that you may find lower voltages as for the Vgg and Vdd.

Or you can try to change the LED display. Although plausible, I´d not bet on this because I do not think the LED´s would dim after time.

In time: I completely disassembled three TI59 card readers and reassembled one of them with the best of them. I found out that the one in best working conditions had a different layout in the head terminals, and the other two had gooey 'rubber roller' (is it the correct term for that stuff?), and I ended up with a few good components. Because I have another TI59 under repair, I'll try to wire the whole reader with pieces of flat cable used in high speed IDE hard disks (I always forget how many conductors it has...). I'll record the whole operation in pictures and let you all know ASAP. All of this will be done after delving into the so well known 41CX motherboard...


Luiz (Brazil)

Edited: 19 Jan 2010, 4:58 p.m.


Thanks, Luiz! I'm well. I certainly wouldn't waste too much time on the TI-59... except out of interest in its repair. I bought so many of them so cheaply when I first started collecting that I have lots of parts, including some card reader assemblies. And for you, I'd be happy to send you a fully functioning 59. With their prices rising, I've been trying to add a few more to the "pile" just for fun, but I have plenty of them.....

Let me know if you want a bunch of 59 parts or just a working one... spend your time on those wonderful HP's!



Hi, Doc;

you see, the only two TI´s I feel confident about using and repairing are the TI58C and TI59. The TI58 seems to be almost like the TI59, but the TI58C has a different circuit. The reason is simple: technology timeline and history. I almost worship these two models because they were way ahead of their time when they appeared. Their printer (PC100C) was external and could be shared amongst models (HP had the printerless HP67 OR the HP97 with built-in printer, and the affordable HP34C), they could also share the Solid State Software Library (ROM modules, available later only with the HP41) and they had plenty of memory. They were fast too, but if we inspect the diagrams (again) we´ll notice that they had a 4-bit data bus (RAM TMC0589, A.L.U. TMC 0501 and C.U.'s TMC 0582/0583) that would allow many operations to be performed in less cycles. Standard and Library ROM's use a serial access (Q1, Q2 control lines) similar to the one found in the HP41. That´s what I like most: to inspect their 'guts' and assimilate them (am I a BORG? Should resisting be futile?)

Click to enlarge (big one, 1.2Mb)

My first calculator ever was a TI57 (still have it, still works) and I used it in the first one and a half years of the University. A fellow mate. The first TI59, along with the PC100C, was a gift from a a former colleague (retired teacher) at the university, and it worked for almost two years. The other two were bought at local e-bay (mercado livre), but none of them are working. The one in the picture (rightmost, over the pale box) is just the empty case. The TI58C (over the PC100C box) works fine, but has a problem with the memory. I was given an old unit and will try to make one fully working out of the two.

The next pictures show one of the card readers. I tried to replace the gooey roller but I could not find a fine replacement so far. All of the other components seem fine (after a 'heavy' cleanup).

Click to enlarge Click to enlarge

I cannot lie to you, doc (afterall, you are a psychologist, why should I?). I'd love to have a working TI59 as part of the 'family'. As you can see in the pictures, there´s a lot of magnetic cards waiting for being read and listed so I can register their contents and operation. I like to 'reverse engineer' these programs and retrieve their flowchart and 'working mechanics'. My brain cells take this kind of activity as relaxing... (should I look for help?)

Well, doc, I guess that the next step is to send you an e-mail with my actual address, right? Can I use the regular e-mail from the MoHPC contact form? Is yours updated? Mine is not, so I must contact you first, if using a valid MoHPC contact e-mail.

Thank you very much. And if there is anything I can do you for, you know you can count on me the same way.


Luiz (Brazil)

Edited: 19 Jan 2010, 7:48 p.m.


Try mlmeyer (at) cox.net. The TI-59 took me all the way through college ('79-'83), and I was able to re-write every computer assignment for it, even with alpha-numerics. (Boy, did that take some time, but you got quick at it...) Let me know if you want a printer with that :).




The TI-59 took me all the way through college ('79-'83), and I was able to re-write every computer assignment for it, even with alpha-numerics.

Mine took me through graduate school and beyond. Yes, alpha-numerics was a big plus for using the printer cradle. I was a huge fan of the 59 ... until I got into HP's.

Hi Luiz!

Happy New Year to you and all in the forum!

Just for a quick comparison, here are pictures of the huge SR-52 card reader I repaired in 2005:

The motor and capstan are gigantic!



Edited: 20 Jan 2010, 1:57 p.m.


I'm impressed. I bought about a half dozen SR-52's years ago. Of those, I was only able to get one to work reliably after rebuilding the card reader. Another works intermittently... won't read cards well. The others had various faults to the keyboards, readers, etc. from corrosion. The SR-52's keyboard plate and connections seem especially prone to destruction from outgassing. I've kept this in mind as they appear online in auctions. I hope that people paying top dollar for an unknown SR-52 don't discover this the hard way.


The PC-100C's printhead is really prone to light printing and sticking. Cleaning it with a cotton swab is easy... open the latch and wipe with alcohol. Close the latch and advance some paper through it.

It also does make the very coolest sound when printing...


And it's pretty fast because a line is printed in parallel without a moving head. Mine had a problem with the driver circuit after maybe a year of use. A friend of mine helped me repair it. On a later occasion when I tried to revive it, the processor seemed to have given up. It locked the calculator completely. :( It was a PC-100A which worked with both my SR-56 and the TI-59 acquired later. The TI no longer reads cards and the keyboard is bouncy.



If you ever design anything like that, do the customer the favor of leaving the rubber out if possible. Something like a sprocket advance with a row of holes in the card like movie film has along the edge would make for a system that would not rot or turn to goo.


I repaired several at about the same time by gluing a rubber plumbing washer on the motor, powering it externally, and simply grinding it down to the right size visually. IIRC, you can adjust the tension on the roller when it's reinstalled. I had good luck with this, but as I joked in an earlier thread, I ended up finding my own advice when looking to see if anyone had found an easier or better way to do this....

This is true for the TI-59. The SR-52 roller has to be exactly the right size and at exactly the right tension, making it very difficult to replace. There's no way to adjust it except to start over....

Edited: 21 Jan 2010, 5:38 p.m.


While we're on the subject, does anyone happen to have the SR-52 service manual? I obtained a paper copy from TI back in 1977 or so, but unfortunately it's long gone.

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