Casio C-80

Casio C-80

This is it – Casio’s first calculator watch, launched 1/1/80. At least that’s as close to the launch date as its possible to get given the lack of official documentation from the parent company.

Don’t get me wrong – I hold Casio in high esteem as innovators in their field and, for a company that is forward-thinking, why should they pay homage to the products of the past that are now outdated and superseded (several times over)? All the same, it would be good if there was some accurate data on release dates, production numbers, that kind of thing.

They do have one document – called the PINDEX – which you might be able to find with a Google search if you’re lucky; that lists some useful information but take the accuracy with a grain of salt.

So it launched on 1 January 1980, with all the other variants using the same module – C-801, C-70, C701, C-60 – but seems to be the one the company favoured above all others if the catalog scan is anything to go by. The gloriously spongy rubber buttons (that on later models become metal) meant you could use the tiny calculator with your fingertips – instead of having to rely on a stylus like the other Seiko and Citizen calculator watches of the time.

Unfortunately, some people didn’t read that part of their instruction manual and used a stylus anyway, meaning finding an early Casio calculator watch with a keypad that isn’t scratched to buggery is very unusual. Those that crop up on eBay today either have broken rubber buttons or heavily scratched metal ones which is a shame, as it is a stunning looking watch.

If you looked up the words ‘nerd watch’ in a dictionary, the C-80 should be photographed next to the description. It is the epitome of form and function with loads of buttons and a high cool factor (particularly if you bought your first computer around the same time the watch was released).

If you find one, cherish it; you are holding a piece of real history in your hands. From here, Casio developed a steady stream of calculator watches incorporating games, scientific functions, melody alarms, solar power, countdown and databank functions, pedometers and more – but all were modelled on the C-80. The look changed in 1983/84 when the keyboard buttons were replaced with a membrane keypad, then touchscreens, but the beginning of the LCD revolution belonged to the C-80 and its ilk.

Casio should have this next to the Casiotone CT-201 on their Chronology of Main Products page (and, for that matter, the MG-880 calculator too!).

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57 Responses to Casio C-80

  1. I gave a perfect case for a C 801 and want to find a replacement working watch to swap the insides over.
    Two questions if you can help
    Can I look for working C 80’s and 801 ‘a to fat a fine or only the C 801? Any idea where I might find one please?

    • Hi, you can put any 133 module in your watch, so you can widen your search to include C-60, C-70, C-701, C-80, C-801. What is wrong with the current module?

      • Thanks for your reply
        I took the watch to get the battery checked and was told that the battery had bled.
        Can this be repaired

        • Short answer – maybe. Depending on how much bleed there’s been, the module could be fixable or not or somewhere in between. A lot of 133 modules have a quirk where the watch runs but none of the buttons work, making it nice for display but useless as a watch. While the 133 is getting rarer, it’s still relatively easy to find a working one (although it can be expensive). If you want to try fix it yourself, buy some isopropyl alcohol, cotton buds and one of these budget kits, use a clean table with plenty of light and disassemble the whole thing. Clean the circuitboard (and everything else that either looks wet, or with caked green gunk on it) carefully but thoroughly with the isopropyl. Reassemble, put new 381/391 batteries in it (you’ll need two) –they’re also called LR1120 batteries – maybe buy them from the $2 shop and if the watch works then buy some Energizers or Maxells. Once the batteries are in, use the tweezers from your repair kit to touch the back of the battery panel and the AC contact at the same time, and cross your fingers that you’ll suddenly see 12:00:00 when you take the tweezers away. If you were careful and it didn’t work, start looking for another…Here’s one I sold only a month or so ago, they’re awesome watches — good luck with yours!!

    • i found one brand new in a store,for 10 bucks,couple of years ago and i didnt buy,coz i didnt know,that is worth that much among collectors,now i know,and i will regret,for life.Greetings from Serbia

      • Go back to the store! It might still be sitting there. You’d be amazed how many NOS watches from the 80s pop up from old jewellers and watch shops (particularly in Italy for some reason).

  2. Thanks for the very helpful reply, I have purchased the kit printed off your instructions and live in hope.


  3. Finally got around to taking it apart (only took 7 months) however it not going. If your still visiting this site would you mind explaining the bit about the tweezers as I cannot figure out the AC contact as its a DC battery. I presume that the back of the battery panel is the metal cover that is screwed on after the batteries have been installed but where is the AC contact??
    Help please

    • Look at the back of the module – really closely (you might need a strong light and a magnifying glass until you find it the first time, after that you’ll know what you’re looking for). One of the holes on the back of the module will have the tiny letters AC next to it. AC is for All Clear (or something like that) rather than Alternating Current. The back of the battery panel is indeed the metal cover. NB there should be a circle of plastic covering one of the sections on the battery cover, if that’s not there, your watch probably won’t work either. Good luck.

  4. l thats the end of that journey – didn’t work! Can i send you the case and strap and defunct inner as its not going to be of any use to me. Give me a call if you want it. I like you to have it for helping me and the case is in very good condition – XXX-XXXXXXXX call or text your address.thanks for your help and hope to hear from you


  5. Thanks for posting this. Got one recently for my daughter. The case is great looks as new as the one I had in 1980. Batteries of course leaked but not as bad as some I have seen. Cleaned it up and put it back together and the calculator, stopwatch all functioned. Thought it was great until I could not set the time.

    Took it apart cleaned some more and afterwards the watch will no longer switch to the calculator or stopwatch. I still can not set the time.

    Its a bummer as the AC reset works on the watch. Could have waited till midnight on Monday to set it LOL.

    Is there a service manual. I did a complete tear-down and it had what appears to be two timing crystals and a surface mount capacitor? It would be worth replacing the capacitor and timing crystals.

    It seems to be pretty hard to find a 133.

    • Hi Jim, your C-80 looks to have succumbed to the unpredictable and frustrating issue affecting the QW133 module. I’ve had success with the QW133 and QW134 by stripping the module and soaking just the circuitboard in pure (or as pure as you can find) Isopropyl for 10-15 mins then scrubbing with a soft toothbrush, and reassembling when dry. No guarantees but I’ve revived several dud modules this way. With the time setting, did you have a manual, or know the procedure? You go into calculator mode, and press buttons for the time (e.g. 8.15pm would be 815∙ then the set button (second from top on the left hand side)). Likewise the date of 25 April 2017 would be 890425 in calculator mode then hit the set button (2017 is the same year in the perpetual calendar as 1989 and the C-80 only goes up to 1999). It’s definitely worth trying to fix, they are getting rarer.

      Also, the timing crystal is probably fine if the watch is ticking over the seconds correctly. You can pick a dud one when the watch is working at twice the speed (I’ve got a video somewhere of this, I’ll post it sometime). It *may* be worth replacing the caps if you can find replacements of the correct or similar value, and if you have the right equipment but TBH I don’t think this is where the problem lies since the caps are often upconverters to boost the voltage so the LCD display is strong particularly on more complex watches.

      • It is sad after the first cleaning of the batteries it ran great but I just could not set the time. I was doing it wrong.

        Until reading on here about the AC reset. The watch would do all sorts of garbage. Random numbers and it would seem to run super fast (sometimes) if you could even get time.

        I looked up the manual after the fact. I only wish I had when it was all working as I could get into calculator mode to enter the time. I can’t now. Which is very strange.

        When you say soaking the board you mean all of it to include the timing crystals light and main IC fully dunked fully in the Isopropyl? Basically not the case and screen. I had taken in apart and wiped it down but did not soak it.

        Do you know what size screws it uses?

        • Yep, soak the whole board once you’ve stripped off the easily removed components like you’ve described. I wouldn’t recommend wiping it unless you’re very careful (cloths have a habit of grabbing onto things like light bulbs and breaking them). A kids toothbrush is ideal but again do it carefully.

          The screws used in the module are a standard size for early 1980s Casios with most sharing the same thread size, just different lengths and head sizes. Service manuals for Casios are uncommon, or perhaps just haven’t been scanned and dumped by those who own them whereas there are a lot of early Seiko manuals around.

  6. She’s alive, she’s alive!! Just wanted to report back the the soaking, brushing and drying (resetting AC) and now all the functions are working!!

    Thanks for your help!

    • Awesome! I always like to hear when an old classic is brought back to life. The soak and scrub trick doesn’t always work (battery acid is a nasty thing particularly when it gets into the traces) but when it does, it’s great.

      The QW133 module isn’t the weirdest setting procedure of old digital watches (it’s up there, but there are some that are really unintuitive like the Nelsonic Space Attacker and Caravelle World Time Melody watches) so always try and find a manual before diving in with screwdrivers and tweezers just in case.

      • I should have remembered it as I had the watch new as a teenager. My daughter is going to love it. It is strange I have repaired many things with leaking batteries. This had very little and no corrosion. Just the clear liquid none of the green stuff.

  7. So my daughter was enjoying the watch and something that I was afraid of happened. The bad snapped. 30+ years old…

    Can you recommend any replacement bands?

    • eBay is your best shot for a genuine replacement — do a search for Casio CFX-20 band (it’s the same one) — they are usually USD20 plus shipping when available.

      BUT I’d only recommend that if you are wanting a display piece, not a daily wearer, since these replacement bands are old stock and deteriorating daily so will probably break just as yours has before too long. Get one anyway, but only when you want to restore total originality to your watch.

      The better replacement would be a non-Casio band — search eBay for Casio 22mm band and you’ll find the generic ones. They fit the watch fine and will last much longer even though they’re not a genuine part.

      You could just get your daughter a CA-53W calculator watch — they’re still plentiful, cheap and easily replaced — and box up your C-80!

  8. Hi there!!! Greetings from Merida, Venezuela!!!

    I just bought a Casio C-80 on eBay which was my first (and only) calculator watch back in the day!!!

    One problem though, it has only one part of the wrist band (the one with the buckle fortunately) but I need to find the other part.

    Would any of you here have that part? Interested in selling it so I can complete (and wear) my watch?

    I’d really appreciate it!

    Thank you all and congratulations on such a killer site!!! Love it to bits!

    • Hello and thank you for your kind comments. The C-80 band is the same as the CFX-20 (as far as I know). There’s usually a couple for sale on eBay but you may have to search for CFX-20 band to find them ~USD20.

  9. Hello Liquid!!!

    This website deserves much more visits!!! I’m super hooked.

    I think I found a deal! Take a look:

    And only $9!!! So I’m on it! Hehehe…

    If you see the picks, it comes with this weird kinda white “chalky” stuff on it. I imagine that’s totally normal from the time it’s been put in storage?

    Keep in touch,

    Alejandro “Alex” Level

  10. Hi Liquid!!! I finally have my super pristine C-80 here with me in Venezuela! Got it from eBay as I mentioned. The seller said that it didn’t turn on. So when I got it, took it to a watch tech (really old guy) he put the 2 batteries in and it worked!!! This technician was like WOW! Where did you have this watch put away for so long? It’s perfect! Even all the rubber buttons are intact and the glass is too! I got REALLY lucky. Only down side is it’s missing one of the bands. I need the side with the holes. It has the side with the buckle on it. And it’s the original 1980 band (intact also). Do you know who may have that original band I need?

    • Awesome – glad you finally snagged one. Check the comments above for the best source of original and after-market bands, eBay will be your best bet.

  11. HI…I’ve got myself a clean piece of C-80 recently. Can you advise if newbie collectors such as myself should keep the watch with batteries in the watch i.e. watch is functioning and telling time, or should I take the batteries out and leave it as a display piece?

    • Hi, I leave batteries in all my watches and check them reasonably regularly (fortnightly/monthly) to check they are still running. I figure a watch without a battery might as well be a broken watch and if you want to wear it ever, why not have it working. Some watches (like Seiko G757 or D138) are sometimes hard/impossible to revive if the batteries have been left to go flat but it also depends if you want to keep buying batteries for watches you don’t intend to wear. Absolutely personal choice — as long as you are using quality batteries the chances of them leaking are slim, but if you just want to stick it in a box then not much point in keeping it powered up 🙂

      • Hi Liquid

        Cheers for the quick reply. I certainly would want to wear it from time to time…was just curious if old watches like this would be more prone to LCD leaks if it’s left running…if that makes sense.

        • A few things can contribute to LCD leaks but I haven’t heard of a battery being one of them (could be wrong though). Generally the LCD will degrade over time anyway, some are just constructed better than others. Things that will hasten bleed are (a) the module not being assembled correctly or not sitting correctly in the case, placing undue pressure on the LCD; (b) dropping the watch or banging it against a hard surface; (c) extremes of temperature. If you have a battery that ran hot for some reason, it could stress the LCD but that’s a bit of a rarity. If bleed is a concern, keep an eye out for dead QW133 module watches with good LCDs — it never hurts to have a spare!

          • Hi Liquid

            Got the batteries changed out for a pair of LR1120 and the LCD came on well but now I have 2 issues:

            The side buttons dont spring back to its original position when depressed and I can’t seem to adjust the time. When I press the reset button…only the seconds will reset but the reat of the time ie hours and minutes won’t change.

            Any advise? Cheers!

          • Hi Garry

            If the side buttons aren’t springing back it’s *possible* they are clogged with years of dirt and other detritus but more likely is that the module isn’t sitting in the case properly.

            The early Casio calculator watches take a bit of extra care to get the module positioned correctly. Start with the case face-down and use a small screwdriver or tweezers to make sure the eight side buttons are pushed outward. Then put the module in base-first (ie the calculator part first, followed by the screen) all the while checking with your tweezers that the side buttons remain pushed outward. Before putting the caseback on, hold the module gently but firmly and test the side buttons.

            To change the time enter calculator mode and enter the numbers for the time (e.g. 8am would be 800) then hit the set button (side button second from the top on the left). The watch should return to time mode and be set to the time you have entered. Same with the date, bearing in mind you’ll have to find a year that corresponds to 2018, I think 1979 or 1990 are the applicable ones. So to set to 5 Feb 2018 you’d go into calculator mode and type 790205 and hit the set button.

        • I’m the guy who posted here on July 25th, last year! I was living in Venezuela but had to move to Chile. Things are really bad over there. So I’m looking for original bands for my C-80 and I’m gonna take the advice you gave me on the CFX20 band which looks exactly like the C-80’s band. Except mine has the silver buckle instead of black. But I’ll exchange them! I’d like to grab another Casio now. One with alarm. Which model would you recommend?

          • Which model would I recommend? Probably all of them!! If you like the C-80 a lot, I’d start looking for a CA-85, CA-86 or CA-90 which will give you an alarm AND a game. Or maybe the CA-95 if you want a calculator watch with multiple alarms and a melody (Scarborough Fair). If you are looking for a non-calculator watch though…your choice is just about endless 🙂

  12. Hello there! I´m looking for a specific model and I cannot find it… it had Scarboough Fair in one of the week´s alarm, but id DID NOT had a calculator. It was around 1982 that I had it… any idea which model that would it be? Thanks!!!

    • The only watch I’ve heard with Scarborough Fair is the CA-951 which does have a calculator. There were plenty of watches with multi-melodies – 7, 16 etc so it was likely one of those.

      Good luck with the hunt!

  13. Hi Liquid!!!
    Hey y’all!!!

    Greetings (again) from Chile. Hope you’re all doing good.

    So excited! I just received a package! A Casio CFX-20 Scientific Calculator watch in the mail a couple days ago I bought from this page called “MercadoLibre” which is a sort of eBay but here in South America (there’s one for every country down here)!!! I also snagged a Casio DBC-62 Data Bank Calculator watch from the same seller. I’m really diggin’ both watches now.

    I’m the same guy who bought a Casio C-80 on eBay for $10 only!!! That one is in (very) pristine condition. It just doesn’t have the original bands. So, now that I have a CFX-20 AND a C-80, I think I may just buy the original bands for them both…

    I think the only thing “wrong” with my CFX-20 is the fact that the top-most button on the right side ( ÷ ) doesn’t reach enough to make contact and simply doesn’t work. So I opened up the back. And discovered somebody replaced the original button with some other one since the section that is supposed to make contact inside has like a sort of “cotter pin” but it’s round and miniature. So that’s I think whats preventing it from reaching the contact inside. I need to find an original CFX-20 button. Do you know who or where I can find one? Or how to look for one?

    I took pictures, but I don’t know how to publish them here so you can see what I’m talking about.

    Talk to you later!

    Take care brother!!!

    Alejandro Level (originally from Venezuela but now living in Chile)

  14. Keep an eye out for a broken one to replace it with — CFX-20, CFX-200, CD-40 and CD-401 use the same case and buttons (although the 40s are black and 200/401 is silver. You’ll have to replace the whole top row. Sometimes you can buy just the button assembly NOS on eBay — keep looking 🙂

    • Hi Liquid!

      Oh, I was talking about the buttons on the sides. The “divided by” button (upmost right side) that’s the one that’s not making contact. So no division, or clearing of the stopwatch functions.

  15. Hi,

    Just found my old C-801 in a drawer.I got it when I was nine years old.
    Replaced the battery and now it is up and running.
    However, it is running to fast.
    Is that possible to fix or is it some componen that hase aged?

    Best regards,

    • Hi Erik, make sure you have performed the AC reset procedure (metal tweezers against the top of the battery cover and the AC contact. This is often all you have to do to make it run correctly again. If that doesn’t help, you’re probably best to start looking for a donor circuitboard to use since the problem is almost certainly in the chip itself. The other thing you could try is replacing the 32,768mhz crystal which *might* be the cause, but it’s usually the chip if the AC reset doesn’t fix it.

  16. Hi Liquid! I have several of these watches (and still looking for a CA-503). As a kid I had a CS-83, but those models keypads tend to disintegrate. I can fix them cosmetically, but the inner printed circuit once separated, I could not fix them as you did with you CA-503.

    Anyway, my question is about the CD-401. I have one, and as soon as I put the backplate, the alarm or buzzer starts to sound until the battery dies. Do you know something about this?

    • Hi Claudio, usually if there is erratic behaviour it’s either hardware or software. Hardware-wise, Casio (and other manufacturers) often included insulators, which were usually just thin plastic cut to shield the required components, to stop short circuits. It’s possible your CD-401 is missing an insulator which may have been discarded at some time in its past. Or, also hardware-related, make sure the back cover is on the right way around. If the pin that’s meant to touch the ceramic speaker is instead earthing on the caseback, it can cause erratic behaviour too.

      Software-wise, assuming corrosion from old batteries hasn’t leaked its way along the traces and into the chip, can often be fixed with an AC reset. Get some thin metal tweezers (or a paper clip if you don’t have tweezers handy) and touch the AC contact on the + of the battery. See how this goes – good luck!

  17. Hi Liquid. Fabulous site!
    I’ve recwntly found all my old watches from the 80’s. A Casio databank and a c-80 amongst them!
    I figured out the problem with the missing “battery cover” but not which one should be covered. I’ve taped over both of them at the moment, and that has made it all work!
    The buttons need cleaning but I’m glad to have got this far!
    Could you tell me which battery should be left uncovered please?
    Let’s call them the “c” battery and the “=“ battery as those are the buttons they are next to.
    Ir does it make any difference?

      • Ah excellent. I also saw a YouTube video swapping internals and it looked like that side so I’ve just done it-all running well.
        I need new buttons to use it as a calculator…and a strap…so I may go the metal
        Route and look out for a faulty
        Watch with a decent shell.

        • You can buy NOS replacement buttons reasonably often on eBay. They aren’t cheap but are, at least, new. Breaking up old cases for the buttons can be a bit hit-and-miss, particularly as they’ve usually been scratched and dinged over time.

  18. Hi Liquid,

    Great site! I need your help! I have a C80 that was working perfectly until a few weeks ago but the display then faded badly – I assumed batteries. I tested the old ones and strangely one was still full power but the other one was totally drained.

    I bought a cheap pack of batteries to quickly test but the display is still very faint after swapping. Possibly a bad battery in the pack you think, or is module itself the problem? One thing I notice is that the light is also very weak, maybe this indicates a power problem. Would a fading LCD also affect the light output?

    I think the previous owner also put the plastic circle on top rather than underneath the metal cover. How significant is this circle can you advise?

    Best Regards

    Richard from Ireland

    • Hi Richard – yes, the plastic disc is important, and where it is placed. It can stop the watch working or present unusual behaviour if it’s in the wrong place.

      A fading LCD won’t affect the light since the light is powered before any power goes to the chip. If the light is weak too (and if it makes the LCD fade more when you press it) it’s definitely a power problem.

      Get some good batteries (Renata, Energizer etc) and seat the plastic disc in the right position and you should be good to go.

      • Thanks Liquid, All sorted! I put the plastic disc in the right place and also checked the ‘new’ batteries. One was fine but the other read around .4 volts. Moral of the story don’t assume new batteries are any good. Both display and light now bright, and Energizer batteries on their way.

  19. Hi Liquid!

    I have a Casio C-80 but most of the front buttons don’t work (just the buttons “2”, “3”, and “+”). I inspected the module and press directly the metallic holes with a metallic pin and they don’t work (just the same buttons work). Any idea of how to solve the issue?

    Thanks for your feedback.

    • Hi, if you’re lucky you’ll find that there is a break between the common grounds on the lines which aren’t working and you can repair it with some silver conductive ink. If not, though, it’s probably a fault in the chip itself which you won’t be able to repair and you’ll have to start hunting for a replacement circuit board. Good luck!

  20. Hi, I have a clean looking C-80, swapped new batteries in it and did the AC reset. It switched back to 12:00, but most of the buttons don’t work ; only the light is working. Nothing else. Reset it a couple of times and some times it ran at double speed. Sometimes it ran at normal speed after the reset. Do you have any ideas about troubleshooting this ? thanks a lot !

  21. Hey you guys!!!

    Good to be back after so many years!!! I’m the guy with the C-80 (and now some other ones too!).

    Question. My C-80 has the grey rubber buttons. Is that the “first edition” or something like that? Because I see a lot of C-80’s with the metal buttons online (it makes me envious, haha).

    Btw, where can I get new grey rubber buttons for mine?

    Take care brothers and sisters!

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