SR-52 not writing cards

[Kees Bouw]

My Texas Instruments SR-52 can't write cards, as it turns out. I repaired it a few years ago and never tested this before. I got it from eBay and it is in beautiful condition, almost new. Very little used I guess. There was a segment missing in the display so I replaced the led stick with one from a donor machine. I repaired the card reader which went very well. It reads cards without any problem. But when writing a card, the motor stops when it is halfway in and the display shows a flashing zero. Of course I covered the write protect window like it says in the manual and I checked photo's on the internet to make sure I did it correctly. I also tried some variations where I covered more or less of the surroundings. None of it makes any difference, the calculator behaves as if I inserted a write protected card. I do not know how the write protect mechanism works exactly. There is an optical component consisting of an LED and a sensor transistor. I think it has the number SDA313 on it. Which (component) failure could cause it to behave like the write protect window was not covered?
One other thing, probably unrelated to this issue: I found a loose part in the calculator near the display and I can't figure out where it belongs. See the attached pictures.
Any help is greatly appreciated!

[Didier Lachieze]

I don’t know what is causing this failure but on Katie’s site you can find the SR-52 Toubleshooting Guide with the schematics.

[Kees Bouw]

(03-30-2023 07:59 PM)Didier Lachieze Wrote:  I don’t know what is causing this failure but on Katie’s site you can find the SR-52 Toubleshooting Guide with the schematics.

Hi Didier,

Thank you very much for the link, I had already seen that document. Unfortunately my knowledge of electronics is quite limited so I am having trouble deducing from the schematics what the problem could be in this case. I was hoping someone in the forum with personal experience with troubleshooting the SR-52 would have some tips about where to look or what to try.

Kees.

[John Garza (3665)]

If you don't mind the question, what material did you use to repair the drive roller in the card reader? I haven't found anything the exact size, so I end up with one slightly larger then hand turn it down to size.

Also, I've found it helps to replace all the tantalum capacitors on the board. If they are not off spec now, they will be soon.

-John

[Kees Bouw]

(04-04-2023 04:23 AM)John Garza (3665) Wrote:  If you don't mind the question, what material did you use to repair the drive roller in the card reader? I haven't found anything the exact size, so I end up with one slightly larger then hand turn it down to size.

Also, I've found it helps to replace all the tantalum capacitors on the board. If they are not off spec now, they will be soon.

-John

Hi John,

Thank you for the advice regarding the tantalum caps. I will replace them, even if it does not fix the problem it is still an improvement.
I repaired the drive roller with a piece of silicon tube, as can be seen in the attached photo's. I can't remember where I got the tubing from but I imagine this size must be available somewhere. Silicon tube is used a lot by aquarium enthusiasts. I noted a few measurements: the diameter of the shaft was 4.46 mm and the diameter of the silicon tube after it was put on was 8.46 mm. I did not use any glue or adhesive, I stretched the tubing a little and it stayed on on its own.

Kees.

[John Garza (3665)]

Well, it's definitely not aquarium tubing. The stuff you're using is much thicker. I've used the standard silicone fuel line tubing from model airplanes to repair HP classic card readers, but never found the right diameter for the SR-52 - even tried several samples from Amazon with no luck.

Can you tell me the inner and outer diameters of the tubing before you mount it on the shaft? That might help locate it.

Thanks,

-John

[Kees Bouw]

(04-08-2023 04:27 AM)John Garza (3665) Wrote:  Can you tell me the inner and outer diameters of the tubing before you mount it on the shaft? That might help locate it.

Thanks,

-John

Hi John,

Sorry about the time it took to answer your question. The outer diameter is 8,25 mm / 0,325 inch and the inner diameter is 3,9 mm / 0,153 inch. Both measured with a digital caliper on the unused, unmounted tubing. If you like, I can send you a piece of tubing if you PM me your address details.

Kees.

[brouhaha]

(04-14-2023 07:20 PM)Kees Bouw Wrote:  The outer diameter is 8,25 mm / 0,325 inch and the inner diameter is 3,9 mm / 0,153 inch. Both measured with a digital caliper on the unused, unmounted tubing.

Thanks for sharing the dimensions. I also need to repair several of my SR-52 calculators.

I see that McMaster-Carr has part number 3242K13, "high-temperature soft rubber tubing for food and beverage" made of "semi-clear silicone rubber" in 4mm ID, 8mm OD, in 10 and 25 foot lengths, for $1.76/foot. 10 feet is a lot more than I'll need, but I may give it a try.

[John Garza (3665)]

Thanks for the measurements. I've never come across fractional mm tubing (at least on Amazon). I've tried the 4mm id 8mm od and that doesn't work very well.

But after a little experimenting - I've found some Amazon-available 3mm id 7mm od that works.
The 3mm id is small so it's a tight fit. But once it's on it expands the outer surface of the tubing to the right diameter. Too tight for CA glue on the inner surface - it just squeezes it out when you mount the tubing, So I add a drop or two on the 'face' with the tiny screw on the end of the shaft and touching the sides of the tubing material.

The 52 is very touchy about pressure on the card as it relates to card speed. I seem to run best with 1 small square of blue painters masking tape replacing the long-dead foam strip on top of the motor housing. And I'm careful to not over tighten the two screws holding the housing together.

And covering the optical Write-Protect sensor with tape doesn't work for me. Maybe my tape surface is too shiny? Not sure. I just use the standard little black tape rectangles applied to the cards.

Ah yes... now where did I put that SR-52 Games Library....


-John

[Kees Bouw]

(04-16-2023 02:30 AM)John Garza (3665) Wrote:  And covering the optical Write-Protect sensor with tape doesn't work for me. Maybe my tape surface is too shiny? Not sure. I just use the standard little black tape rectangles applied to the cards.
-John

Hi John,

You wrote "tape doesn't work for me" but what exactly happens? Does the card just stop half way in (when writing) like it does for me? And what are the "standard little black tape rectangles" exactly?

Kees.

[John Garza (3665)]

Yes it does stop prematurely and no data is written to the card.

The 'normal' way to do this is to attach TI-supplied bits of black adhesive tape to special areas of the cards. The problem is, over the years many will ooze adhesive and fall off or slide around. The tape itself is flat black with a rough surface - excellent for stopping light. A smooth slick black tape (like electrical tape) may fail for this reason as a substitute.

-J

[Kees Bouw]

(04-16-2023 11:58 PM)John Garza (3665) Wrote:  The tape itself is flat black with a rough surface - excellent for stopping light. A smooth slick black tape (like electrical tape) may fail for this reason as a substitute.

-J

What kind of tape do you use as a substitute for the original TI tape?

[John Garza (3665)]

Sorry for the delay. I use the originals. I managed to buy a couple of 52's that came with some sheets of them.

[Kees Bouw]

Status update. The trouble was that when writing cards, the card stopped half way in. This was the case with and without a write protect (or rather: write enable) tab on the card. I thought initially that stopping half way was normal behaviour if you try to write to a card without a tab and that there was something wrong causing this to happen even if there was a tab present. So I opened the calculator to check for anything visually wrong. Everything looked as it should be, but to make sure there were not any reflections I glued some black paper on part of the metal strip that holds the pressure pad. See the attached photo. I also did some testing and found that the card ran completely through when writing. I attributed this to the photo-transistor not being in the correct position. I put the calculator back together again and... now writing cards works fine. Which is great, but the downside is that I still have no idea what was wrong. I really don't think that covering the metal strip solved it, if this could be a problem then TI would have done so in the factory. Anyway, it turns out that stopping half way is NOT normal behaviour when writing a card without tabs. What really happens is that the card runs through but there will be a blinking zero in the display to indicate that writing did not succeed. If I had known that beforehand, I would possibly not have wasted time and energy on finding working tabs.

[vassilisprevelakis]

Hi all,

A bit off topic, but I'd like to ask if the capstan wheel on the SR-52 is the same size as the TI-59 capstan wheel.

I am trying to fix my TI-59 but so far I have had no luck finding any kind of info on the 59 wheel.

Best Regards

Vassilis
http://www.series80.org

[Kees Bouw]

(04-27-2023 11:49 AM)vassilisprevelakis Wrote:  Hi all,

A bit off topic, but I'd like to ask if the capstan wheel on the SR-52 is the same size as the TI-59 capstan wheel.

I am trying to fix my TI-59 but so far I have had no luck finding any kind of info on the 59 wheel.

Best Regards

Vassilis
http://www.series80.org

Hi Vassilis,

They are definitely not the same size. The SR-52 uses a bigger and simpler construction of the card reader, the TI-59 is more complicated and also has a gearbox. The simpler design means that less things can go wrong, I found the SR-52 card reader once restored properly quite reliable. I am sure that lots of information can be found on the internet about restoring a TI-59 card reader, just google "ti59 card reader repair". There is even a repair kit available on eBay. This is a bit expensive but it works well.

Kees.

[vassilisprevelakis]

(05-01-2023 10:18 AM)Kees Bouw Wrote:  I am sure that lots of information can be found on the internet about restoring a TI-59 card reader, just google "ti59 card reader repair". There is even a repair kit available on eBay. This is a bit expensive but it works well.

Hi,

Well so far I have not found any specific info on the size of the capstan wheel. From the deteriorated capstan of my TI-59 I can guess that the outer diameter is about 8mm, but I can't be sure because the capstan was already gooey. I have tried silicon tubing with an OD of 8mm but there is slippage. My guess is that's a bit too wide, so probably needs a bit of sanding.

I can do it by trial and error, but if anybody has the figure it would sure help to speed things up.

Thanks

Vassilis
http://www.series80.org