Casio AT-550 Touchscreen Calculator

Casio AT-550 Touchscreen Calculator

Casio’s AT-550 (and its variants, the AT-551 and AT-552) used the [320] module and were incredibly technologically advanced for their time (I know I say this a lot, but you have to remember that this was 1984 and it would be a good 10 years before similar technology appeared in Palm devices – and maybe even SMART devices today!)

So Casio made oodles of analog-digital watches and most were reasonably ho-hum, analog time with digital alarm, date and stopwatch.

But the AT ‘Janus’ watches were something else. They included an eight-digit touchscreen calculator.

And not the kind of calculator where the touchscreen was a grid and each square represented a calculator key (like the TC-600). This time the entire touchscreen could be used to ‘write’ the number or calculator function and the watch would recognise what had been written by the user’s fingertip and perform the calculation. If reading that doesn’t blow you away, it should. Again, this was 1984 — Apple had just released the first MacIntosh!

Casio went a step further with this in the DB-1000 when they added database (alpha-numeric characters) functionality, but they had a full LCD screen to work with there, on the AT watches, there was only eight LCD digits at the top of the screen.

This watch really is amazing, fully working models change hands for around US$200+ and it’s worth it.

The downside? Sometimes they break. Usually it’s the analog portion that stops working (and these are a nightmare to disassemble, I wouldn’t recommend it unless you know what you’re doing). I’ve transplanted pieces between like AT models with great success and, theoretically, you could replace the analog with one of the more generic analog/digital Casio units (which are much cheaper) but I haven’t tried this so am only guessing.

The AT-552G is, for some reason, the most common of the AT series. I’m not sure why but that’s generally the model you’ll see on eBay and can still be had for a reasonable price. I’ve owned several of the gold ones but don’t like wearing gold all that much. The AT-550-7 in the photo above, though, is my favourite of the lot and will often give it an outing. Definitely one to buy if you see a 100% working model for sale. If either the analog or digital portion is broken though, you possibly shouldn’t bother.

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29 Responses to Casio AT-550 Touchscreen Calculator

  1. Hiya! Amazing weblog! I happen to be a everyday visitor to your internet site (somewhat much more like addict ) of this website. Just wanted to say I appreciate your blogs and am searching forward for a lot more!

  2. I have a Casio AT552G. All the digital functions including the touch screen calculator are working but the analog is not. Can anyone suggest a possible fix or recommend a repair shop? Casio tells me that they no longer repair this watch.


    • Check on eBay for a banged-up but working AT-550/551/552, or one with working analog. Then find a watchmaker you trust or if you’re really keen do the transplant yourself. I’ve done a few now (the analog always seems to crap out) but the first couple were a bit nerve-wracking 😉

      • Teste a bobina, se estiver funcionando pode ser o magneto (motor) travado ou mal colocado.
        Tem que usar uma lupa, e tem que ter muita paciência e calma, isso se nenhuma peça estiver danificada.

    • Hi, first you have to remove the bracelet (both sides – don’t try and shortcut it by only removing one). Once the bracelet is off you’ll see both ends have notches holding the caseback on. VERY CAREFULLY slot a small screwdriver under one end and lever until it pops up. Then do the same on the other side and you’ll be able to lift the caseback off.

        • Hi, if you don’t have a watch pin remover you can achieve the same result with a sewing pin. You’ll see holes at either end of the case lugs, poke a pin in and you’ll feel it on the springbar. Put a bit of tension on the bracelet at the same time you’re pushing the pin and it will pop out. Good luck.

  3. I still have my Casio At-551g and just got a new battery at a fine jeweler. It works like the day I got it back in 1987. The original band wore out and I got a replacement in the early 90s. Surprised it is still in good shape AND RUNNING!
    I don’t know if I wanna sell it or not. I was going on 20 when I found the watch at a Pittsburgh store. I’m 50 now.

  4. Just got my watch, replaced the battery and it didn’t work… displayed loads of random number on the display and didn’t tick, then I took the battery out and back in again and it worked!


    The calculator function doesn’t seem to work… does anyone know why? or how to get this working again, are there screen replacements and how does the screen connect to the main board?



    • Hi James, the touchscreen and module are connected by a small zebra-strip. If you removed the module this may have fallen out or become misaligned, but since removing the module would require also removing the crown and isn’t something you’d need to do for a simple battery change, it’s a bit unlikely. Most probably it hasn’t reset itself properly after the battery change (the garbled display would also indicate that).

      If you have a look at this image:

      You’ll see a pin next to the letters AC. Use a pair of metal tweezers to touch this pin and the back of the battery.

      When you flip the watch back over the display should look normal and be counting from 12:00:00 again.

      If your calculator still doesn’t work after that, it may be something a bit deeper, but this normally resolves 99% of issues like this.

      • Thanks for replying 🙂

        Cheers, I will give that a go tonight, randomly last night the touch started working, but then stoped worked after a few goes.

        I’ll keep trying and report back soon.

      • Update,

        The reset worked, however I have a very odd different issue, with the back case on , or off, when I press the top button on the left, it cuts the power out to the watch?

        Any idea at all how to fix this,



        • If it’s something that’s only just started happening then the module may be sitting a little askew in the case, or have a foreign object (like a screw) that has dropped somewhere it shouldn’t and is shorting out when you try to use the top button. The best way to check for this is a close visual inspection or maybe blowing it with a can of compressed air.

          Also check if it does it all the time, or only when the caseback is on. I haven’t taken the back off my AT-550 for a while but generally if there is any thin sheets of plastic on the back of the module, or in the battery bay etc they are there for a reason and usually to stop components shorting against each other or against the caseback.

          Make sure the battery is well-seated as well (like the picture below) and that its contacts are clean.

          Generally, unless the module is fried, these kinds of things can often be identified and fixed.

          • Thanks for getting back to me,

            It’s very intermittent on working, sometimes after a reset, it works, then stops working, I’m not sure whats up with it and there is nothing but this forum online haha

            Is there somewhere, like a trusted casio repair place I can take the watch to be repaired in the UK/London that you know of?

            Really like this one and I’d love to keep it, thanks


          • Hey,

            I tried to join the forum but no luck. Now my watch doesn’t turn on at all, I had the battery out for a few months. I’ve tried the contact join, and nothing 🙁

            Not sure how to get it back alive, ive tested the battery and thats fine,

            Any ideas? anyone that can fix this beauty of a watch?

        • Dê uma olha com uma lente nas trilhas da placa do relógio, também pode ser os capacitores smd com solda fria. No meu deu esse problema e era os capacitores smd.
          Cuidado ao tirar o pino que acerta as horas (os ponteiros de horas, minutos e segundos). E muito mais cuidado ao colocar esse pino, pois ele pode raspa a placa e romper as trilhas e parar o funcionamento do relógio.

  5. I have an AT-550 that I have had since it was new (provided by Casio for me doing research on various calculator-watch entry methods; published in Applied Ergonomics way back in 80s). Hadn’t used for years but pulled out this year to fire up again. The analog and digital portions are working fine. However, the buttons are seized up. My initial suspicion was dissimilar metals corrosion. Watch repair place here looked at it and wouldn’t touch the buttons, but then nobody in the shop was well acquainted with the watch, and only one person was old enough to know about it. I haven’t tried anything yet as I tend to be cautious. Has anyone encountered this problem and effectively dealt with it? I want to avoid introducing any contamination into the case if at all possible. Thanks in advance.

    • I’ve seen stuck buttons on a number of the AT watches (and the non-calculator, but similar cased AQ series). The problem is generally not the usual combination of dust, sweat and general gunk that affects other watches but a combination of small pushers and holes, and the base metal corroding under the plating causing rough spots. My fix has always been to look for a tiny circular file and clean/smooth the holes then look for good buttons from dead watches. Good luck!

  6. Really informative article any advise where I can purchase one as I am trying to buy one for my son for his 18th

  7. My granddaughter(9) and I were talking about the ‘olden days’ of b&w TV and got onto the subject of calculators and computers and how large they were compared to today’s smartphones, etc. After she left, I remembered my old AT-550G Casio and dusted it off. After replacing the battery, I got all manner of strange symbols in the display. Took your advice and used tweezers between the AC terminal to ground and it began working once again! Went through the setting steps and all went well UNTIL I tried to set the year; the solid state module only recognizes years from 1984 through 2019 – 35 years! Impossible to input 2020 or any other year up to 2084. That’s a good example of the limits of electronics back in 1984. BTW, it’s working beautifully both analog and digital!

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