1970s Commodore Scientific Calculator Restoration

[@ytteman]

The dangling thing with black shrink wrap is a step-up voltage converter. The rechargeable model was powered by 3 half-length NiCd cells in series, and the voltage from them was not enough for the calculator. The cells were configured physically as 2 + 1, with the step-up circuit in line with the single cell. The step-up circuit doubles the voltage by creating a negative voltage equal to the battery voltage. Red/black is battery plus/minus, and the blue is the negative voltage output.

[@JanBeta]

Thanks for pointing that out! Makes complete sense! :D

[@zadzwon112]

I am just working on SR4148 with identical power supply arrangements. Do you mean PCB runs on +3V, 0V and -3V? On PCB there are labels VSS = positive voltage and VGG = negative voltage and "-" which I guess is 0V.

[@a_walk_down_memory_lane]

I love the design and color scheme of these 70s Commodore calculators

[@ct6502-c7w]

Yeah, earlier electronics definitely had much better style to them. I really wish they would bring that back. Everything is so drab and boring now.

[@mrjsv4935]

Very nice Commodore calculator :) Love that glowing red display, looks so futuristic. My dad had some calculator in the 70's - early 80's which had green glowing numbers, that too was quite fascinating as a kid :)

[@stevetodd7383]

Back in the day I used to live within bike riding distance of the UK Commodore factory where they made these things. A little bin diving on a weekend and some soldering work let me revive rejected models. I managed to get one of their SR-9000 series models working, which was hugely sophisticated for the time, with 10 memories and 90 odd functions covering trigonometry, statistics and a bunch of other stuff. It made teachers eyes bulge when I whipped it out to answer questions 😊

[@ct6502-c7w]

Very cool! I have a small collection of vintage calculators, and I especially like the displays. Much better than modern dull monochrome LCDs. Earlier electronic devices also just had more style to them.

[@JanBeta]

Wow, that's awesome! Thanks for sharing! I can imagine that calculators were not a common thing back in those days. I am slightly too young to have witnessed that revolution first hand (I used bland LCD calculators in school and uni which were super inexpensive and readily available at the time already). :D

[@ArtimusPrime2025]

Hey man. I discovered your channel not long ago, and now I am hooked on it. I grew up with Commodore computers (I still own an A500, and I've also owned a 2000 and a C64.) I'm really enjoying your content. Keep up the good work!

[@JanBeta]

Hey, thanks! I focus on Commodore because that's what I grew up with, too. (C64s and Amigas, not so much their calculators). :)

[@cleaverbrad]

I love you Jan Beta! Thank you another great video!

[@gerteldering]

Hi Jan, seeing that you are having fun with it! If you look closely on the registration on the back you can see that it has a different type number, I think it says SR6120R, which has a lower number of digits on its display.

[@JanBeta]

Hey Gert! Thanks so much for sending me this piece of history! I am indeed having a lot of fun with it already. It's definitely going to be put to good use in the lab. :) Did you replace the back cover at some point or is the different model number just a Commodore mixup? Interesting anyway. :D

[@dennisp.2147]

It's interesting that Commodore, which was still a Canadian company in 1975, would use US Bicentennial marketing (Minuteman '76) on a calculator sold in Europe and manufactured in the UK.

[@JanBeta]

Very international! I guess they were aiming high even at that point.

[@meh3247]

Speaking as a reluctant Englander (& permanent Northern European), I chuckled at your "Oh the irony" comment regarding the EU power adapter! Cheers for that!

[@JanBeta]

Yeah, I couldn't resist making a little comment about that whole disaster... Glad you caught it. :D

[@wimwiddershins]

That's a thing of beauty. CBM bubble display!

[@JanBeta]

Gotta love those crisp little displays! :)

[@Colin_Ames]

An entertaining video, as always.

[@iNimbleSloth]

Loving those retro hand-drawn PCBs.

[@JanBeta]

Yes! They are absolutely magnificent. :)

[@tubical71]

Congrats Jan, Now you own a nice CBM. Years ago I found a SR-4148 at a local fleamarket. Sadly it still had the NiCads inside which, of course, leaked heavily... I needed to give it an depth cleaning and also rebuild some traces, replaced nearly all passives and that 'flex' cable as well. Also mine didn't come with any power supply (it had cost only 10 bucks, non working) I designed and built a regulated one myself with went in the space where that NiCad pack originally was located. Now I can run it from anything above 6 volts AC and 9 volts DC and no need to worry about polarity. But in the end I had, and still have, a nice golden C= age, scientific calculator. It's def. worth the time and effort. 👍😊

[@JanBeta]

Nice! These old calculators are magnificent pieces of history indeed. I plan on using mine with a modern power supply that I'm going to put the correct connector on (already ordered a suitable one) which should be very convenient. :)

[@CalculatorObsessed]

Another great video, and this time with my favourite era of calculator/ calculator display. The calculator uses a 14 digit display to display a 10 digit mantissa and 2 digit exponent, with the digit preceding the mantissa and exponent used to display the sign of each. Hoping to see more calculators in the future, and important part of the computer story. Also interesting from a manufacturing perspective to see how costs were cut over time.

[@pdaguytom]

Glad to see these old calculators get some love! You might check around, but on a lot of the old calculators with the "built in" nicad batteries, the battery was a buffer for in-rush current when the calculator was being charged/powered from the charger. Great video!

[@JanBeta]

Good call! Maybe it would be a good idea to just put a capacitor on those battery connections to replicate that behavior to some extent. I guess putting a new battery in is probably not very wise (because leakage etc), I plan to use it with a power supply anyway.

[@DavoidJohnson]

I remember getting one for my birthday from my wife in the seventies. One with fewer functions battery only, which kept me amused for the day.

[@ultrametric9317]

My first scientific as a kid was a Commodore. You cannot imagine how even this primitive machine was a gigantic upgrade over a slide rule. A typical sort of problem I needed to solve involved 4 angles, 3 cosines and 2 sines, 3 multiplications, a subtraction and an addition, and then an inverse cosine. It took several minutes at maximum speed using lookup tables of functions. I could suddenly do that in 15 seconds even taking into account the slow speed. I wore it out. A year later I got a TI programmable. I wish I had kept the Commodore.

[@datassetteuser356]

Very nice work, I like old calculators, especially the ones from Commodore. Good stuff! 👏

[@JanBeta]

Thanks! I love them old calculators, too. The displays are just amazing compared to the bland LCDs we get these days. Keyboard feels awesome to type on, too. :D

[@sonic2000gr]

I was given one of these to service a few years ago. The on-off switch needed cleaning. After that it worked flawlessly.

[@JanBeta]

The on-off switch seems to be the weak spot on these indeed. The ICs appear to be very resilient indeed. :)

[@TheSeanBean]

Nice. I have a SR4148R. Very similar to yours, but i have extra buttons instead of needing an F key to access those functions. Mine is in good condition but keys have UV yellowing. I dont fancy taking it apart again to Retrobright. Your keys look very fresh.

[@Felice_Enellen]

When I was in grade 19 akgebra, in the mid 80s, someone had a very similar late 70s scientific calculator their father had given them. I think it was a TI. One of the nerdy things we used to do was compare how long each other's calculators took to perform 69 factorial. His took several seconds while new(er) calculators took maybe a quarter second to a half second. One day I bought and brought in a brand new programmable Casio and it did it instantly (I suspect it just did a table lookup since the number format could only hold up to 69 factorial) and that was the end of the factorial races.

[@MicheIIePucca]

I still remember in 75, we went to the shopping mall and saw "small" Texas Instrument calculators for the first time. People were crowded around the counter top where they were "mounted down" to prevent theft. It was incredible to see something like this do math so easily, and people were amazed. Luckily when I did tech school it was in an era when calculators were around, and I can't imagine going through it without one.

[@JanBeta]

Nice! Thanks for sharing! I am slightly too young to have witnessed the revolution that these portable calculators must have been but I imagine they were a real game changer at the time. I used bland LCD models during my "career" at school and uni in the late 80's and 90's. Would have been a whole different experience without them being available (and really inexpensive by then) when I got to that point in my life. :)

[@markianclark9645]

My walk down memory lane takes me back 50 years..to I think 1974..might possibly be late '73..my first pocket calculator the Commodore 776M..similar to your black one but in beige..I was an office lad about 17 years old and needed to share the desktop mains one with the lady several times a week..desk calculators cost a fortune then..way out of my price range..but then these were introduced about 1973..9volt battery pocket model..i saw in Selfridge's London west end only a few hundred yards away from the offices..and affordable £9.95 or 9.99 a tenner basically..it was very useful at work for a while..less competing for time on the desktop one..still needed that for printouts but most of my job was double checking for errors so the pocket one was ok for that..i still had mine in the 80's but i guess it got replaced and i didn't care where it went..pity

[@djdoo]

A beautiful little scientific calc fully loaded with all the needed maths! The scratch on the display at center it is caused by the pouch itself from the push button of the lid. Sadly a mistake in the design of the protective case otherwise this thing seems that it was made to be used and last the usage, cheers from Greece!

[@JanBeta]

That makes sense! I didn't realize that the scratch exactly matches the position of the pouch button. I might just add a little padding to the backside of that to prevent more scratches!

[@gertsy2000]

Well done Jan. Great work. I couldn't help but notice (:)) that there is just a tiny bit of silver showing on the top front label. A tiny dab with some black enamel nail polish on the tip of a toothpick will cover that. Also could it be the inside of the press stud on the cover is what is burring the display?

[@JanBeta]

Thanks! I didn't notice the little spot until you mentioned it. I'm going to try to fix it up. I think you are right about the stud causing the scratches. I am going to put some padding on the inside of the pouch I guess. :)

[@me0262]

11:45 Another method of removing a stripped screw is to take some needle nose pliers, grip it around the screwhead, and torque it. It sometimes works, sometimes not, dremeling a flathead like you did is also a good way to do that.

[@velutumbra]

The scratches in the screen are from the pouche's button

[@JanBeta]

Yes! Makes sense. I'm going to put some extra padding in the pouch to prevent further scratches, I guess.

[@necronom]

You mentioned it was made in the UK, so that will be the Stockton-on-Tees factory that's in the next town along from me. I've driven past it several times. I know 3 people who have been in it (one when it was CBM), but annoyingly I haven't.

[@JanBeta]

Ah, that's unfortunate! I guess it's been repurposed or demolished by now? :/

[@necronom]

@@JanBeta I think this is the original building. It's a community church now, though I think it was a chemical companies office at one point: www.google.com/maps/@54.5316292,-1.3596868,3a,75y,27.95h,88.3t/data=!3m6!1e1!3m4!1sRbEoCg9IvxZrdWu9czWgBQ!2e0!7i16384!8i8192?coh=205409&entry=ttu

[@JendaLinda]

Pro tip: you can put the wrist strap on your leg, so your hands will be free. It doesn't need to be on your wrist because the whole human body is conductive and there's a large value resistor inside the strap anyway..

[@JanBeta]

I know! I wear it on my wrist for being able to quickly remove it when I work on devices that I have to power from the mains while testing. You don't want to be connected to ground (even if through a resistor) while accidentally touching something mains powered.

[@frankb575]

Dremel with a Proxon 😂 good work!

[@JanBeta]

Should have called it "rotary tool" probably. But that doesn't roll of the tongue as smoothly... :D

[@watchmakerful]

Recently I found TWO identical Commodores, branded Privileg SR80D-NC. Very similar to this one (and with the same CPU), but VFD instead of LED. One required VFD replacement (by a Soviet tube from Electronica MK-61).

[@JanBeta]

Nice! I read somewhere that these were sold by different brands internationally. The VFD displays were marketed as the "green line" if I remember correctly. Very cutting edge technology at the time!

[@watchmakerful]

@@JanBeta Yep, "green line". But they did not put this name on their scientific devices.

[@erikreimann5556]

A calculator with 11 digits plus an exponent is still considered professional today! I wonder how much something like that cost in the 70s

[@gerteldering]

I can tell that exactly, because it belonged to me. It was 199 Dutch Guilders in 1976 of 1977. With correction for inflation it would be a little over 300 euros now. At the time I sent it to Jan I looked if I could still find the original sales slip, but I couldn't.

[@DetroitDiesel671]

"PolyWatch" is a plastic polish for watch crystals... Just what you need for the display.

[@TheGreatAtario]

"Gription" "Hero side" Someone's been watching Adam Savage videos :p

[@JanBeta]

Indeed. :D

[@tenminutetokyo2643]

You can still find these LED arrays NOS if you search hard.

[@thelostc]

Excellent Commodore Calcolator restoration! I Wanna one. What the model is it? 😊

[@JanBeta]

This one is the SR-6140R. They had many other similar ones in the lineup, some with even more functions. :)

[@thelostc]

@@JanBeta thanks a lot!

[@BerndFelsche]

Looks like the scratch in the display is from the press-stud of the case.

[@JanBeta]

Yes! That makes sense! I might just add a bit of padding to prevent further scratches. Thanks for pointing that out. :)

[@6LordMortus9]

I wonder if painting the boards with nail polish would be a good idea or not.

[@JanBeta]

I don't think it would hurt but given that the boards survived fine since 1975, I don't think it's necessary really.

[@cheetahspot]

Did I miss it or did you never reveal what the shrinktube mystery thing dangling from the red and blue wire is?

[@gerteldering]

I think it was the regulator for charging the NiCad batteries. I took the batteries out when they stopped charging.

[@JanBeta]

A commenter pointed out that it is a step-up converter to slightly raise the voltage from the original rechargeable battery. Which makes sense. Probably they included the little circuit in the rechargeable models to make up for the slightly less powerful battery and left it out for the "disposable battery" models.

[@DavidB-rx3km]

Steve Jobs sold his early calculator to fund the starting of Apple - can imagine how much those really early ones were worth.

[@JanBeta]

They were pretty costly at the time, I assume. This was very much cutting edge technology in the 70's. :D

[@christopherhewett340]

Engineer brand make screw removal pliers that may assist with those small screws rather than having to take to it with a Dremel.

[@weedmanwestvancouverbc9266]

I hope you go into the math chip a bit and see what kind of accuracy you get out of it

[@raythomas4812]

lovely buttons and as you mention, no CBM is no more , after all they stuff they did from then until they went under- sad

[@rager1969]

I thought you were going to remove the electrical tape to see what was in that little pack.

[@JanBeta]

I didn't want to destroy it. A commenter pointed out that it was probably a voltage doubler circuit or a step up converter to make up for the lack of voltage from the original rechargeable battery. Makes sense. They probably added the little pack to the rechargeable version and left it out for the "disposable battery" version.

[@SamuelFlint]

Why not make an adapter to let you run it off USB-C then you can use any modern battery bank?

[@JanBeta]

I'm going to look into that! I tried running it from 5V but it didn't quite suffice to power it so a regular old-school USB adapter is not going to be enough. USB-C should be feasible though.

[@hikarustarr]

should have tested it by writing 80085

[@davidlloyd1526]

"25 seconds ago". I click fast :)

[@Adam-rt7lp]

Super fast

[@pintokitkat]

😅 but, but, but why didn't you investigate the shrink wrapped dongle? What was it? Don't just ignore it! We need to know

[@JanBeta]

I still don't know for sure (and I didn't want to rip it apart to not destroy it). Somebody commented that it was a voltage doubler circuit because the original battery didn't provide enough voltage for the calculator. Which totally makes sense. They probably added the little thing to the rechargeable models and left it out of the "disposable battery" ones.

[@cobblehillsfighter]

Never power this power jacks before you connect them to device, as they positive shorting on the gnd before fully seated, and destroy the transformer in power brick

[@JanBeta]

Yeah, the phono connectors for power are generally not the smartest connector. :)

[@brianwild4640]

See if it will run on 5 volt then you can do a usb to phono cable 👍🏻

[@JanBeta]

I tried with the bench supply, but 5V don't seem to be enough unfortunately. It powers on but then instantly crashes. I guess the additional circuitry brings the voltage down enough so that the chips don't get enough juice. 6V seems to be the lowest voltage that makes it work although the chips are 5V. I guess it could be modified to run on 5V (by connecting the voltage to the spots where the original battery went) but I don't really want to modify this museum piece any more than absolutely necessary.

[@twocvbloke]

Calculators can be problematic with some mathematics, all thanks to BODMAS, modern calculators 9aprticularly the apps on phones) calculate using BODMAS, but traditional ones, such as this, do not, and they can produce different answers due to the way they process the numbers entered, it confuses me, but there's smarter people out there who know how it all works!!! :P

[@gerteldering]

If you look at 2:29, you will see a manual page that describes an error that this calculator had. For some arguments in trigonometric functions it wouldn't display an output and you had to circumvent it. On the bottom of the page to the right of it, I noted where it still worked and where it didn't.

[@gabrielleeliseo6062]

We call that "leather" PLEATHER...as in (plastic)leather.

[@JanBeta]

Makes sense! :D

[@lezbriddon]

had a commodore one what would say sqrt of 25 was 4.9999999, wished I had kept it but I got a refund

[@JanBeta]

That is nearly accurate at least! :D I tried it on this one in the follow-up video and mine displays the correct result, actually. I doubt it would be possible to get a refund for it so phew... ;)

[@MichaelEhling]

2:06 hee-hee

[@JanBeta]

I couldn't resist commenting on that... :D

[@chrisrobson8540]

good job.....and not a 5318008 to be seen 🤣🤣🤣

[@JanBeta]

I try to resist using that. ;)