Sorry.
A few lines somehow developed into ‘long read’.
Technically, not exactly a Christmas present, but I did find something I’d been looking for for years, and all but given up on.
History
Not my first calculator, but my upgrade from the Sinclair Scientific I built from a kit only a few years earlier, and had been trouble free. I have to make that clear since so many people now feel the need to kick Sinclair.
I got my original Texas Instrument SR-51A II some time after the mid 1970s, and have to say I loved it from day one. It all just worked smoothly, there were no crazy keystroke sequences needed to access frequently used functions I needed, and (something I only learned after having to use others), the keyboard was just right too. No stiff/hard key presses that needed too much force applied to register a keystroke, or the other extreme, where key presses were so soft and woolly that there was no tactile feedback, and every keystroke had to be carefully watched over to make sure an adjacent key wasn’t accidentally given the merest touch, and registered as well.
But, there was a downside – after only a few years, I turned it on one day, and was presented with some weirdly flickering digits.
With everything contained in only a few big ICs, there’s no real chance of fixing such a failure, although I did dive in and look for any bad/failed solder connections, or perhaps something loose/damaged. However, it was a waste of time, and no amount of poking or prodding made the slightest difference.
Needing a fast replacement (they don’t pause university degree courses or wait for you to get going again), I only had a day or so to find something similar as the SR-51A was no longer available! If not obvious, there was no handy Internet, websites, or web browser to help. All the info was on paper, in magazines, or pamphlets, or found by walking to shops to look at options.
Suffice to say that in the time available I made the mistake of thinking the TI-58C Programmable would be more of the same.
Did I say mistake?
It had all the functions, and was of course programmable.
But an SR-51A replacement it was not.
It was a loathsome device, with all the functions I used to be able to get direct access to fenced away behind the Second Function key, which had to be pressed EVERY DAMNED TIME!
But, I’d made my scientific calculator bed and, as an actual poor student, had to lie in it, since I couldn’t afford to try anything else.
Can’t fix it – can I replace it?
A few years ago, the old SR-51A bubbled up to the top of my pile of goodies, and was still just showing those same frustratingly flickering digits.
But, now we had the Internet, and eBay, so I started hunting.
There was a steady stream of survivors being offered for sale, but they were almost always being sold for ‘Spares or Repair’. Working models were either looking for silly money, or looked dubious, so I almost gave up.
Seems I did miss out almost as soon as I started looking, having found one for sale in Switzerland from what looked like a reputable seller, however I wasn’t an eBay user, and just wasn’t sure.
I watched for a few weeks, and studied the pics – apparently working, it had also been converted to lithium power with the triple AA NiCad pack replaced by a small lithium cell and an adjustable voltage converter and charger fitted into the battery pack space.
On reflection, I think it was fine, but while I was “Doing my research”, trying to find out the range of prices, and how available they were, it was bought.
I kept looking for some years after that, but nothing as good appeared again.
To be honest, I’d all but given up all hopes of getting a working example.
Most were being sold in America, with the carriage seldom less than almost £30 (this has dropped recently), and always ‘Untested’ or ‘Parts only’,
Slightly more reasonable costwise are examples from Germany, but they have the same issue, “Untested”, and having watched a few, never seem to sell, and can look rough inside – broken battery terminals and/or corrosion. So probably useless except for display, and not really worth the asking priced, even if the carriage is better than from America.
There’s probably no point in buying something like this, as there’s no way of telling how far the corrosion has crept along the tracks, maybe even along the legs of the ICs and inside the packages!
2025 Surprise
My occasional glances contused the same pattern, expensive carriage from America, ‘Untested’ from Germany.
Then the pattern changed one day – a reasonable price, UK postage, and a description that did not claim or state the calculator was working, but neither was it explicitly spares or parts only. I’ve come to learn that means if an item is non-working, chances are you can claim your money back from eBay.
Going through the pics, it looked almost mint and, if it was real, one of the pics even showed a lit display.
I walked around my living room about 500 times that – then hit the BUY button.
Does it work?
Yes it does 😁
The win.
Boxed, with manuals, UK charger, soft case, and some receipts.
Strangely, the box is well worn (obviously the same age, mine still looks brand new, and is printed for the SR-51A ll), and I’ve come to the conclusion the calculatoe spent most of its life inside, only being taken out when needed, then stored away after use.
Both calculators are labelled SR-51A. Mine has nothing indicative of the ll shown on the box.
I’ve examined the components on the boards, and both carry date codes suggesting they were manufactured around the same time, with no apparent differences to their builds. I haven’t seen any details regarding the ll designation on any of the calculator history websites, so don’t know what it may signifiy, if anything. Maybe the code was altered in later models to fix bugs, or just make it more efficient?
The NiCad battery pack looks almost new and original, and has no corrosion. Given it should date from the year of manufacture some time in the late 1970s, that’s unusual. Mine looks pretty bad, and was fortunately NOT left in place. I think it has to be a recently manufactured replacement item as it looks similar to some I’ve seen pictured for sale. They’re also an example of price gouging, being only three NiCad or NiMH cells in a carrier, these packs cost almost as much as paid for this calculator.
The soft carry case is another item that looks as if was never used, except to store the calculator.
I thought the receipts would have told be about the calculator, one being for a purchase, and one for a repair (in the 1970s), but when I checked the serial numbers and other details, found they related to another calculator belonging to the same owner.
Those were the days when shops included the serial numbers on receipts!
In fact, the calculator looks almost unused.
The only complaint I had was that the (female) owner had scratched her name into the gold coloured from panel, AND painted it on the back panel, next to the charging socket behind the display. This is something I’ve noticed on quite a few of these calculators. Were they THAT desirable in their day?
The only issue I could find after trying to use it was some odd behaviour from the keys – a few would either fail to return when pressed, or were hard/impossible to press. It was very odd, and I couldn’t see a reason at first.
After dismantling the keyboard, I found some very tiny drop of a hard material down the side of some of the buttons.
I’d initially thought some sort of spillage, but that would have covered the calculator, and probably flooded it, and there was absolutely no evidence of such an event.
This was possibly a dozen instances of some tiny drops that somehow got down into the space between the affected button and front panel, then dried hard,
I tried shifting them in an ultrasonic bath, but they seemed to ignore this.
Eventually I shifted them all, one at a time, with a tiny pointed wooden stick and plain water. This seemed to loosen them, and let them simply be pushed off the surface.
It was all somewhat pointless (just for my own satisfaction), as the end game was just to swap the working gits into my own case.
Another surprise
When I compare the internals, I was surprised to find my original had some extra components mounted around the charging socket.
I’d completely forgotten I’d added a miniature LED, resistor, and diode, to provide confirmation that the charger was connected, something sorely missing from the original.
Pointless?
The sad thing is that in 2025, few reach for a calculator for anything repetitive, and all my real numbers are crunched in spreadsheets.
Screw up a long calculation on a calculator, and you have to do it all over again.
In a spreadsheet, you can constantly eyeball and check as you go, fix mistakes, and no need to key everything in again.
For stuff I do need to calculate as I go, then I’ve got plenty of cheap calculators which I can afford to risk/lose/damage, as they now only cost a few pounds.
Later
A few years later, probably after the mid 1980s, I got lucky again.
Still before the Internet, I used to go through the ‘Miscellaneous’ section of the Glasgow Evening Times, just out of curiosity as some odd stuff turned up for sale in the small ads.
Not once, but twice, I found a Hewlett Packard HP-41C for sale in those ads.
The first one was just the calculator in its carrying case.
The second one was an absolute WIN!
This came in a carrying case filled with nearly all the accessories, and an assortment of programming books, manuals, and newsletter from the owner’s club, and documentation on ‘synthetic programming’. Synthetic programming (SP) is an advanced technique for programming the HP-41C, involving the creation of instructions (or combinations of instructions and operands) that cannot be obtained using the standard capabilities of the calculator.
In terms of HP-41C hardware, I have the magnetic card reader, the wand (for reading barcodes), the thermal printer, one of the expansion modules, and the cassette drive.
There was even a rechargeable battery pack, but the NiCads failed early on. The long battery life of the Type N alkaline made it kind of pointless anyway, and there was no danger of them leaking, as regular use meant regular replacement.
It’s worth adding that the alphanumeric display and keyboard of the HP-41C showed just how bad the TI-58 programmable was.
While I used, and programmed many applications on the HP-41C over the years, I think I was only ever motivated to write ONE program on the TI-58 – and even now remember it was NO FUN AT ALL.
The HP-41C can be dismantled (the boards are not permanently connected internally, unlike the SR-51A) and reassembled freely, something I did to find out which combination produced the fastest device.
Notably, given the battery pack has to be removed when doing this, the calculator retains all its programming and works perfecly whenever this is done, despite being made of parts from different calculators, and having had its power source removed for an extended time.
Non-volatile RAM (memory) was fairly rare at the time, and most devices lost any stored date if power was lost for any reason, or needed to have a separate power supply provided to keep the data live.
Secret Scotland 