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SR-52 card reader wheel
02-21-2021, 09:24 PM
Post: #1
SR-52 card reader wheel
Hi everyone

Does anyone know the inner and outer diameter for the gummy wheel of a SR-52 card reader ?
Eventually could be useful the thickness as well
We have looked in few sites but there is no indication of this se sizes

Thanks for help !!!

Edoardo & Alberto
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02-22-2021, 06:59 PM (This post was last modified: 02-22-2021 07:01 PM by Klaus Overhage.)
Post: #2
RE: SR-52 card reader wheel
Post # 18 of this thread contains all you need: "2015's calculator anniversary - the SR-52"
https://www.hpmuseum.org/forum/thread-2804.html

I have manage to bring two SR-52 bake to read cards but write cards is a game of luck. I have one SR-52 with an old green replacement role that can read and write.
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02-22-2021, 07:22 PM
Post: #3
RE: SR-52 card reader wheel
Thank you very much !

I had seen that post and read it because I want to give it a try but I had kind of missed that picture

Has it been difficult to restore yours ?

I understand that is strongly suggested to replace also the soft pad that guides the card, is it true ?

Thanks for any help !!!

Edoardo & Alberto
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02-24-2021, 09:56 PM (This post was last modified: 02-24-2021 09:57 PM by albertofenini.)
Post: #4
RE: SR-52 card reader wheel
Small update ...
We have these two units to practice with
We tried with silicone tubing id 4 mm od 8 mm
Obviously most of the circuitry is missing so we were just working on mechanical issues
The result is encouraging so we will try on our working units and post the result
Any suggestion is very welcome !
Pictures and video here : SR-52 CARD READER

Edoardo & Alberto
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02-25-2021, 08:12 AM (This post was last modified: 11-01-2021 09:19 AM by Klaus Overhage.)
Post: #5
RE: SR-52 card reader wheel
Your work with the silicone tubing looks very promising. I have not replaced the soft pad. I have an SR-52 with a black roller that has become sticky and is leaving marks on the cards. I suppose this could be an old original.

The calculator with the green roller can easily read the old cards in the software packages and it is often successful at writing. I think it is a replacement role built in by a company at the time.

When I was looking for rubber disks from which I can make replacement rolls, I came across the rubber feet of my table-top fan. The fourth photo shows below such a foot and the built-in roller that was made from it with the help of smear paper and a small drill.

Because the cards were drawn in slowly and with difficulty, three layers of yellow Postit serve as spacers at certain points. So this SR-52 can read cards again without any problems.

In your two videos, the cards are drawn in faster and pushed out much further than I know, but it looks good. My calculators stops the engine when the card is 1 cm out.


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02-25-2021, 09:00 AM
Post: #6
RE: SR-52 card reader wheel
Hi Klaus, hi everyone

you must consider that these are not working units, and the test had the only purpose
to verify if the size and the grip of the tubing were compatible, which it looks to be case,
grips is pretty good, while the wheel appear to be a little eccentric which may be a cause
for not reading or writing well in a future working unit

consider that since these are not working units we powered the motor directly with an external 3V
battery pack, and that's why it runs probably faster and doesn't stop when the card is read

it must be said that at the beginning both motors were very slow but a drop of WD-40 in
the back, you can access the rotor removing the plastic cover from the back of the motor
has helped a lot both to reduce the noise and to improve the speed, still remember these
two motors are not calculator controlled, so I presume in real working scenario they may
run at lower speed

we have a little experience on the HP-65 and HP-67 card readers and we presume that
the working method here is probably more or less the same, so I'm expecting that also
here the motor speed is hardware controlled and that the springs in the card reader together
with the optical sensor will stop the engine when necessary

differently from HP-65, HP67 and TI-59 I understand that here the start of the engine
is not due to the insertion of the card but rather to the command 2nd read

we also need to improve (a lot) the way we cut the tubing, with HP models we use o-rings
but the capstan mechanical is totally different, will do more test today and we will probably
start working on a functional unit, just to see what happens

Any idea, especially on how to cut the tube, is very much appreciated!!!

take care !!

Edoardo & Alberto
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02-25-2021, 10:22 PM
Post: #7
RE: SR-52 card reader wheel
Little update
We opened one of our two working units
Looked like never opened before but once opened the card reader was loose and the roller missing
We recovered the roller form one of the scrap units
We cut a thin 3 or 4 millimeters wheel
Put some wd40 on the back of the motor
We noticed that with an inner diameter of 4 mm the wheel tents to slip
However we couldn’t find a inner 3 and outer 8
We will probably glue
First test looks good
We were able to read a diagnostic card and lunar landing
Tomorrow we will try to read more cards and to write as well
Too bad one of the battery contacts broke ...
Pictures: SR-52 953114 LTA4176

Edoardo & Alberto
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02-26-2021, 10:29 PM
Post: #8
RE: SR-52 card reader wheel
Last update
It also writes cards !!
We have successfully copied the lunar landing card
The new card has been partially covered to make it writable
The link has an update video
Things to do : glue the gummy wheel, little more lubricant for the card reader motor and replace the broken battery contact
It has also been cleaned in and out and all the sticky buttons now work perfectly

Update pictures : SR-52 RESTORATION

Edoardo & Alberto
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03-01-2021, 10:01 AM
Post: #9
RE: SR-52 card reader wheel
Hi Klaus

could you please do me a favor ?

In the picture with the Post-it I can almost see how the magnetic head and the card
reader switch and motor are connected to the pcb

this version is different from the one I'm restoring but I also have two units
like this one in the picture

would it be possible to have a picture where all the cables can be seen ?

thank you very much !!!!


(02-25-2021 08:12 AM)Klaus Overhage Wrote:  Your work with the silicone tubing looks very promising. I have not replaced the soft pad. I have an SR-52 with a black roller that has become sticky and is leaving marks on the cards. I suppose this could be an old original.

The calculator with the green roller can easily read the old cards in the software packages and it is often successful at writing. I think it is a replacement role built in by a company at the time.

When I was looking for rubber disks from which I can make replacement rolls, I came across the rubber feet of my table-top fan. The fourth photo shows below such a foot and the built-in roller that was made from it with the help of smear paper and a small drill.

Because the cards were drawn in slowly and with difficulty, three layers of yellow Postit serve as spacers at certain points. So this SR-52 can read cards again without any problems.

In your two videos, the cards are drawn in faster and pushed out much further than I know, but it looks good. My calculators stops the engine when the card is 1 cm out.

Edoardo & Alberto
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03-03-2021, 12:26 PM (This post was last modified: 11-01-2021 09:13 AM by Klaus Overhage.)
Post: #10
RE: SR-52 card reader wheel
Hello Edoardo & Alberto,

this morning I was able to take good pictures of the "post-it-calculator " in daylight. I hope you can see everything important on it.

Best Regards


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03-03-2021, 08:59 PM
Post: #11
RE: SR-52 card reader wheel
Thank you, thank you very much !!!
This is exactly what we needed to try to rebuild those two units
We will try it and post here the results !!
Thanks again
(03-03-2021 12:26 PM)Klaus Overhage Wrote:  Hello Edoardo & Alberto,

this morning I was able to take good pictures of the "post-it-calculator " in daylight. I hope you can see everything important on it.

Best Regards

Edoardo & Alberto
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03-12-2021, 05:48 PM (This post was last modified: 03-12-2021 05:55 PM by jebem.)
Post: #12
RE: SR-52 card reader wheel
Hi, Alberto,

Thanks for your kind words.
Meanwhile my father passed away on 8-March.


Coming to your thread point, I found some old files in my new laptop related to some information made available by our fellow member Etienne and by Froggy as well.

Some of the Etienne information is still available on his website here:
http://etiennevictoria.com/Sr52_wheel/

I am attaching some draft documents collected from Etienne and Froggy information that was publicly available at the time by the authors, related to the card reader rebuild.
If this violate any rules in this forum, I am sure an Admin will let me know and I will promptly remove it from my post.


Alberto, the SR52 troubleshooting guide contains information on how to calibrate the card reader, but we should not follow that information by the letter, as there are so many calculator variants and I suspect that the manual covers only part of it.

I am sorry for not being able to help you on specifics but as I am currently away from home and to be honest I am also a bit disconnected from this hobby as well, although I keep following all the other members publications.

Good luck and please keep sharing your findings and pictures. I am sure this information will be valuable and appreciated by others as well.


Attached File(s)
.pdf  Repairing the SR-52 card reader wheel - Etienne.pdf (Size: 238.76 KB / Downloads: 10)
.pdf  Rebuilding Hp-85 9815 9825 capstan Etienne.pdf (Size: 446.78 KB / Downloads: 8)
.pdf  Repairing the SR-52 card reader wheel - Froggysoft .pdf (Size: 266.01 KB / Downloads: 15)
.pdf  Etienne SR52 card reader details.pdf (Size: 264.44 KB / Downloads: 11)

Jose Mesquita
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03-12-2021, 08:03 PM
Post: #13
RE: SR-52 card reader wheel
Hi Jose

I'm really sorry to hear about your loss,
I have lost mine at the end of 2019 so I understand what you are going thru
please accept my deepest condolences ....

Ifyou have time and use every possible distraction to let the mind go for a while
(as I did at the time) have a look at our other thread : SR-52 rebuild project (SR-52 942058 LTA4176)

We really thank you, your original thread and all of the documentation have been of great help and
we have followed it step by step

We restored the keyboard, found a faulty display forever, repaired the battery connectors
glued back the faceplate and got a almost working unit, but as we described in our last post in that thread,
the card reader is not working, may be you can have some good ideas

Meanwhile we will print the documents you have enclosed and look at them

Again, we are very sorry for what happened

take care, we wish you the best !

(03-12-2021 05:48 PM)jebem Wrote:  Hi, Alberto,

Thanks for your kind words.
Meanwhile my father passed away on 8-March.


Coming to your thread point, I found some old files in my new laptop related to some information made available by our fellow member Etienne and by Froggy as well.

Some of the Etienne information is still available on his website here:
http://etiennevictoria.com/Sr52_wheel/

I am attaching some draft documents collected from Etienne and Froggy information that was publicly available at the time by the authors, related to the card reader rebuild.
If this violate any rules in this forum, I am sure an Admin will let me know and I will promptly remove it from my post.


Alberto, the SR52 troubleshooting guide contains information on how to calibrate the card reader, but we should not follow that information by the letter, as there are so many calculator variants and I suspect that the manual covers only part of it.

I am sorry for not being able to help you on specifics but as I am currently away from home and to be honest I am also a bit disconnected from this hobby as well, although I keep following all the other members publications.

Good luck and please keep sharing your findings and pictures. I am sure this information will be valuable and appreciated by others as well.

Edoardo & Alberto
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