Post Reply 
2015's calculator anniversary - the SR-52
02-07-2016, 05:18 PM (This post was last modified: 02-07-2016 05:35 PM by jebem.)
Post: #21
RE: 2015's calculator anniversary - the SR-52
Thank you for the extra photos of your SR-52A, Etienne!
Nice work of yours.
That FroggySoft information is very useful too. Thanks.

Concerning the card reader motor wheel outer diameter value, I'm not sure about what the correct value must be, because:
- There are several revisions of the SR-52 (A thru L) and at least one SR-52A revision;
- And it seems that there are different versions of the motor body as well (my specimen has a nude metallic body (dimensions published previously), while yours and FroggySoft motors appears to have a sort of plastic cover around the metal body?).

On a very positive note:
I managed to get an original paperback version of the "SR-52 and SR-52A Troubleshooting Guide"!
Among other goodies, it contains specific information on the card reader controller variants and details the adjustment procedure for the photocoupler card sensor and motor speed.

Katie was very kind to host a high resolution (300dpi) digitized copy for easy sharing among us.
Thank you, Katie!

Jose Mesquita member

Find all posts by this user
Quote this message in a reply
02-07-2016, 10:13 PM (This post was last modified: 02-07-2016 10:16 PM by Etienne Victoria.)
Post: #22
RE: 2015's calculator anniversary - the SR-52
Thanks Jose and Katie for sharing the SR-52 troubleshooter !

This is the most interesting SR-52 document I've seen in years.

No more fiddling around blindly with the pots to adjust the card reader :-)

And the circuit schemes of the multiple variants will definitely help.

The SR-52 motor pictured above indeed has a non-removable plastic case. I'll check the schematics to identify the revision nr.

Visit this user's website Find all posts by this user
Quote this message in a reply
02-26-2016, 06:58 PM (This post was last modified: 02-26-2016 07:08 PM by jebem.)
Post: #23
RE: 2015's calculator anniversary - the SR-52
Another small update on my SR-52 restoration saga.

1. The failed electronics issue
After swapping around the IC's from three different calculators, I managed to have one good working calculator.
Once again, thank you Etienne for your "spares" supply !

As I see it, these electronic failures can be caused by over-voltage, as a result of applying energy from the external power adapter without having good Ni-Cd batteries installed (or having corroded or broken battery terminals for that matter).
On top of that, most of the times the battery electrolytes leakage has spread all over the PCB components, and applying energy to the machine will not help at all.

Besides that, there are a few more identified potential issues:

2.- The "flat cable" Keyboard PCA - Main PCA interconnect.
This "16-wires cable" breaks easily, because it uses extremely rigid zinc alloy strips working as unifilar "wires".
This results in multiple key register failures.

I really am annoyed with myself, as I knew about this issue and still, due to careless handling, I manage to break a few of these brass strips.
The cure is simple but delicate to implement. I'm planning to just solder the broken brass legs once I have all the other issues fixed. This will be the last procedure just before installing the PCA in the front cover.

3.- Main PCA broken/corroded zinc alloy battery contacts
This is another very common issue with vintage Texas machines, mostly resulting from battery leaking corrosion.

In order to make new spring lever contacts, I found an excellent German supplier at TAS, offering high quality brass sheet in thickness as thin as 0.1mm.
This material can be cut with common scissors and it is easy to solder.

4.- The motor rubber driver wheel going gummy.
This is a endemic issue on calculators from the 70's from any brand.

As a mechanical component failure is not my area of expertise, I have been learning from good people's work published here and there concerning possible rubber wheel replacement solutions.

Like Etienne's 8.2mm diameter wheel, I find that a 8mm outer diameter should be good enough to drag the magnetic card at a even speed.

To test it, I ordered some silicone hose tubing from TAS.
The inner diameter is 4mm and the outer diameter is 8mm. Not ideal, but very close to the required specs.

I have cut a small slice of this silicone tubing and inserted it into the motor shaft.

Because this motor shaft doesn't have an adjustment system to set the pressure against the pinch roller, I used some extra foam inserted between the motor body and its case, to reinforce the pressure from the original Texas foam.

Using an external power supply, have applied 3Volt to the motor and inserted a previously used card.
The card was dragged at uniform speed, at least from what I can see on my oscilloscope connected to the magnetic head coils.
(I have these old used cards that have some data written by the previous owners, probably more than 30 years ago).
The existing written data generates a stable signal with an estimate of about 6mVpp amplitude (2.1mVrms). I can't be more precise here as my old vintage oscilloscope can only resolve up to 10mV per division.

More to come one of these weeks (I hope).

Right now I'm quite busy on one of our datacenters in Spain with so many virtual appliances to create and validate. Customers comes first. Calculators are a hobby and shall wait.
But of course the goodies found in the Cataluña restaurants like Jamón and vino tinto are really comforting me for having to work so hard. Smile

Jose Mesquita member

Find all posts by this user
Quote this message in a reply
02-27-2016, 01:30 PM
Post: #24
RE: 2015's calculator anniversary - the SR-52
The SR-52 was the first programmable anything that I ever saw. A friend of my parents had one and I still remember him showing it to me while we were for dinner one night. I was completely mesmerized. He let me borrow it and I programmed a prime number finder. It's no exaggeration to say that the SR-52 and that night led to my career as a computer programmer.
Find all posts by this user
Quote this message in a reply
02-27-2016, 01:59 PM
Post: #25
RE: 2015's calculator anniversary - the SR-52
If so, then this was one of the best accomplishments of the SR-52. :-)
Find all posts by this user
Quote this message in a reply
03-24-2023, 05:27 PM
Post: #26
RE: 2015's calculator anniversary - the SR-52
(02-01-2016 11:07 PM)jebem Wrote:  Here is the motor schematic drawing. Dimensions in mm.

Thanks for sharing your diagram. I am a but confused. Is the inner diameter of the roller 2.0 mm or 4.3 mm?
Find all posts by this user
Quote this message in a reply
Post Reply 

User(s) browsing this thread: 1 Guest(s)