The X8 Cosmotron


In 1966 Citizen launched its first ‘electric’ watch – Japan’s first electronic watch in fact – which incorporated what was then new technology to replace the traditional mainspring to drive the movement. Although such a hybrid approach had been introduced years before, Citizen claims this to be ‘the world’s first genuine electronic wristwatch that has adopted a moving-magnet type balance motor, driven by transistor on the regulating device’. (See this thread for some discussion about this claim:

And this is what Citizen say are the benefits of this technology in their technical guide:

The X8 / Cosmotron production run was short, about 10 years in all, since the early 1970s saw the quartz revolution, and older technology was quickly rendered obsolete. However, there was significant development of the technology during its brief history, including raising the beat rate from a conventional 18,000bph at the start to 43,200bph at the end, in those using a relatively conventional balance. The quality of the X8 movement was indicated by its achievement of chronometer standards. This reflects the aims of the electronic technology to increase both reliability and accuracy, both of which were overtaken by the advantages of quartz modules.

The technical guide states ‘in comparison to conventional wristwatches, the construction is simplified by far, and the power conduct is applied in reversed direction’ and also that ‘this eliminates troubles originating from worn or damaged parts which occurred due to excessive driving power’. So we can see that this technology offered advantages over traditional mechanical movements. It would have been interesting to see where it might have got to had quartz not arrived on the scene….

Before looking at the different movements and models, please note that all movements have fine adjusters on the balance and all of them ‘hack’, i.e. the watch is stopped when the crown is pulled fully out to the time setting position – this is achieved by the battery power being disconnected so would also be used when the watch is not in use (battery removal is recommended if stored for an extended period).

The First Model, 0801/2:

The very first version of the X8 was named the ‘Electric Watch’ and used the initial 0801 movement with 25 jewels – so many jewels were no doubt technically unnecessary, as can be seen with the later movements in the line, but these were high grade watches with a high price to match, so the jewel count was important to reflect its status. The movement ran at 18,000bph and to reflect its difference from conventional watches, the first X8 was given a unique look:

(Above Image by ‘Martback’)

In 1969 the X8 Electric name was replaced by the X8 Chrono Master, using the second iteration of the original movement, the 0802 – and included a ‘Chronometer’ grade version (although not marked ‘officially certified’).  ‘Electronic’ was also added to the dial:

The case back is also unique to this model, with an old style case number (ELCS 51201-Y) and a special tool was made to remove it:

The X8 Chrono Master remained in production at least until 1971, but I guess not for much longer than that (it doesn’t appear in the 1973 catalog) and by that time other movements and models had been developed and launched. In the 1971 catalog these early models are shown on the ‘X8 Chronometer’ page, note the one on the left is marked ‘chronometer’ above the X8 logo:

The 0801/2 movement, powered by 1.55v silver oxide batteries, had a tiny rheostat to regulate the balance amplitude which was not needed in the later movements.

Here is an example of marketing for this model:

The 0840 / 0880:

This was the second generation of the movement, running at either 21,600bph (0840) or 18,000bph (0880), and with 12 jewels. It was launched in 1969, and powered the first models to carry the name ‘Cosmotron’ it also had ‘transistorized’ on the dial together with a new applied Cosmotron logo. They retained ‘X8’ on dial, but this was dropped later in the development of the line. The number of models was beginning to expand significantly, with more conventional cases than the first type, along with the later case number type, on this one it’s 4-810139 Y:

Again powered by a 1.55v silver oxide battery, the movement has 12 jewels:

This diagram points out the differences between the first and second generation movements:

The 0820 – Officially Certified Chronometer

This movement, produced in 1970, was officially certified as meeting the JCA (Japan Chronometer Association) standards and as fas as I know was only used in two models. It has 19 jewels, runs at 21,600bph powered by a 1.55v battery and the movement is uniquely numbered. The first model has an unusual case design, and of course carries the ‘officially certified’ logo:

The second model is particularly interesting, in that it was the world’s first titanium cased watch. I understand that only 2000 models were made in 1970 – note that the case back is marked ‘scratch proof. Citizen say that the case was 99.6% titanium:


(with credit to the Yahoo Japan seller)

The 4840:

With 12 jewels I believe this is the same as the 0840, but for the first time has a date complication and was launched in 1970. Here are some examples from 1971, note the bracelet / strap types and case numbers for the different movements:

Still powered by 1.55v silver oxide batteries, and alongside the 0840 versions, there is now a significant range of models in the line up, and more colourful designs were emerging at the start of the 1970s. First some more 4840s:

And some 0840s:

This scan of marketing material shows examples across the range, and includes a pocket watch version:

Inside the 08 Movement: the architecture of the 08 and 78 movements are different, so they are shown as quite  separate lines in the technical manuals. Here are exploded views of the 08 design, which can be compared with the 78 shown further down the page:

The 78xx Series:

1972 saw the launch of new models with both date and day complications, now using the 78 movement. With jewelling reduced to 8, and now powered by 1.3v silver oxide batteries, the movement design has been refined, with more functions. The rate has now increased to 36,000bph, and movements were designated 7801A, 7802A, 7803A, 7804A and 7806A. The X8 name has now been dropped, so dials are marked Cosmotron, Electronic and carry the Cosmotron applied logo.

All these 78 movements have an unusual method for quickly setting the date and day, which I believe no other manufacturer has used. The crown is pushed in to do this when the crown is in the normal running position – to set the date this action is carried out with the watch held vertically, 12 o’clock high. To set the day, the watch is held the other way up, i.e. vertically with 6 o’clock high – with thanks to Noah (SCWF) here are photos which show the lever – sternly marked ‘DON’T OIL’ – which enables the dual function. The day wheel is removed to show the lever. Setting the date – watch is 12 o’clock high (crown on right side of watch):

And now inverted – 6 o’clock high – to change the day, note the tip of the lever is no longer engaged with the date wheel:

The 7803 is perhaps the most interesting of the 78 models, sometimes found in a monocoque case (i.e. single piece, opened via removal of the crystal) with a different case number style – 7800-870xxx. Known as the Cosmotron Special the 7803 models is clearly identifiable by the button it has at the 8 o’clock position:

On this monocoque case (from July 1973) the back has a battery hatch, and a hole covered by a screw down cap (removed in this pic) which gives access to the fine adjuster on the balance:


The ‘special’ nature of this is the action applied by using the button at the 8 o’clock position. This not only  zeros the second hand (to 12 o’clock) but also zeros the minute hand when it is within + or – 3 minutes of 12 o’clock. Currently I’m not aware of any other manufacturer that has employed this feature, which I believe is to allow exact synchronisation of the watch. Also, when the button is held in, the second hand is kept at 12 o’clock until the button is released. If the button is pressed and released the hand is zero’d and immediately restarts, as is found in a ‘fly-back‘ chronograph. Citizen also notes that the Cosmotron Special is capable of chronometer grade accuracy.

Here’s a video of the button in action:

Here is an example of the 78 movement, this one is a 7806A:


And the dial side of this 7806A model:

Inside the 78 movement: here are exploded views of the 78 movement, which can be compared with the 08 shown above:

The IC-12 / 5800

In 1970 Citizen launched the IC-12 – meaning Integrated Circuit – 12 beats per second. This was their fastest beating electro-mechanical watch, with an hourly rate of 43,200. Although initially not badged ‘X8’ or ‘Cosmotron’ they later used the movement – designated the 5800 – in Cosmotron models.

The movement is small and was used in both men and women’s watches, it uses a 1.55v battery. Here’s a catalog image of the men’s model which is an ‘Officially Certified Chronometer’– note the price! (although it is a 14k white gold model):

IC-12 Chronometer Catalog 1973

 This marketing image shows it alongside a woman’s model:

And here’s the 17 jewel movement, an impressive piece of small scale engineering:

By the mid-1970s the movement was being used in Cosmotron models:

The small movement looks rather lost in what is only a medium sized men’s model:

The GX

The final model in the Cosmotron line-up is something of an anomaly, in that it uses a completely different type of movement. It remains a very interesting piece however, since it is a single coil tuning fork watch. Although Citizen made twin coil movements licensed by Bulova as used in the Hisonic, it appears that the GX movement, designated 3701B, was its own design and uses a 1.55v battery. For example the coil is placed on the opposite side to Bulova’s version, and the 11 jewel movement is not stamped as ‘Lic. Bulova’ as is the case with the Hisonic. And, again as in the Hisonic, the battery is positioned with the +ve side away from you as you look at it, unlike all the other Cosmotrons:

The tuning fork movement runs at 360hz – 360 beats per second – which of course gives a very smooth sweep of the second hand, of the sort you might see on a modern day Seiko Spring Drive. Here are two examples, the second of which has an unusual dial colour and finish:

An example of the case back, this one has been engraved:


It’s not clear why Citizen included this model in the Cosmotron line – I can only speculate that it was to preserve the exclusivity of the Hisonic models.

Finally a few scans of marketing material from 1969/1971:

Footnote: I think I’ve covered all the movements and given examples of the related models, but I’m always learning about vintage Citizens so please get in touch if you have information I can add, or which would amend / correct / improve what I have published so far.


83 Responses to The X8 Cosmotron

  1. Jay says:


    I came across this site trying to find more information about the cosmotron I inherited from my father-in-law. It had the 7804a movement with probably the model number 4-790138 y. When my mother-in-law handed it over to me, it was not working. So I sent it over to a local watch repair man. He discovered that the old battery had already leaked and he was not sure whether he could make it work again.

    I was disappointed because I would like to keep it with the family as a heirloom, so I made some research and found a suitable battery replacement, an LR44. Before, I installed the new battery, I cleaned out the residue left by the old battery. Lo and behold, the watch came back to life after I installed the new battery. I’m totally impressed with the build quality knowing that this is a 40 year old watch.

    Anyways, I would like to know more information about it’s bracelet. I think that the stainless steel band is not original. Instead of the expected citizen logo on the clasp, it’s marked ‘elite’. I would like to know what is the original band for this model, as my 79 year old mother-in-law can no longer remember what it originally looked like. I’m inclined to replacing the band with one made of leather but would like to have it as close to original as possible. Thanks.

    • sweephand says:

      Hi Jay, thanks for visiting my blog. It’s great to hear about your father-in-law’s watch and that you’ve been able to clean it up after the battery leaked. My PC is out of commission at the moment so I will get back to you about the bracelet in a couple of days.
      Although the LR 44 is the right voltage it is an alkaline battery and it is better to use silver oxide – these maintain their charge better and last longer. The SR44 or equivalent is the right one and good quality ones are recommended. If you visit the Electric Watches site (see link on my blog) you can find more info and battery types / makes.

      • sweephand says:

        Hi Jay – you may already have seen the original catalog pics on the Cosmotron X8 page, but they are mainly from the 1971 edition whilst your 7804a model is later, probably from around 1974. I’ve found a couple of examples (with credit to sellers on Yahoo Japan) which show two types used with 78xx models. The clasps of the Cosmotron bracelets have the Cosmotron logo on them, as well as ‘Citizen’ – it’s rather faint on the second example but it would be good to find one with this if possible:


  2. Jay says:

    Hi Stephen,

    Your site is a big help. Now I need to find an SR44. The first photo pretty much nails it for my particular cosmotron. Based on the serial number, it’s built February of 1974. I found a similar model off ebay. Here is the link (

    Geez, this watch will have it’s 4oth birthday next month. I just hope by that time, I could be able to source a correct band for it.

    At the moment, I installed a new black leather band. Now it looks immaculate. Some of my friends were fooled that I am wearing a new watch. I’ll send you a photo of it once I get to picture it.

    Thank you very much.

    • sweephand says:

      Hi Jay, you’re welcome 🙂 Although it would be good to have an original bracelet, my personal preference is for leather so I imagine yours looks very good. It will be great to see a pic of it – bear in mind that you can’t upload pics directly to my blog. You can post a link to something like Photobucket, or I can email you so you can send them to me and I’ll upload them. Let me know if you want me to do that (best not to post your email address in a comment though since this is a public blog, I get to see your email when you visit anyway).


  3. Jay says:

    Hi Stephen, it would be an honor to see a photo of my watch in your site. I just hope that the picture will justify the beauty of the dial.

    It has the two tone silver and blue with some sort of hologram effect when viewed at different angles. The effect is awesome. Sort of like Japanese katanas clashing under strobelights. Simply amazing.

    Also, I just noticed yesterday that the day/date changes at noon as supposed to past midnight. Is this normal?

    • sweephand says:

      Hi Jay, I’m looking forward to seeing your watch 🙂 I’ll email you later so you can send pic(s) when you’re ready.

      As for the date change, it’s not really a problem, it’s just that the day/date has been set to a time more than 12 hours before or after the day/date changeover. If it is changing 12 hours late, then simply change the time by moving forwards through exactly 12 hours. That should get it back in synch with your midnight. If it is changing 12 hours early, and since it is a Cosmotron, then you could simply stop the watch by pulling the crown out to the time setting position, and leave it for exactly 12 hours – again that should get it back in synch.

      Do you know how to use the ‘quick-set’ date and day mechanism on this watch? Since it’s a 7804 it is a bit unusual – if you scroll down the Cosmotron page ( to the section on the 78xx series you’ll see an explanation. I’ve known that the day change may not always work properly on these movements, but it’s easy enough simply to wind forward through to the right day, then push the crown in to set the date (the date quick-set usually seems ok). Never try to set the date when it is already going through a changeover since that could damage the mechanism.


  4. Jay says:

    Hi Stephen, thank you for the information. You really are a big help. Hope you won’t get tired doing it ‘coz I think I’ll be needing another one.

    Yesterday, my watch suddenly just stopped. I thought it was just the battery as I was using an LR44 so I replaced it with a brand new SR44W. Still it didn’t work. This morning, the watch suddenly came back to life again but is now running too fast. Twice the normal speed of the second hand.

    I’ve searched for information on-line and found magnetized hairsprings causes mechanical watches to run fast. Does this also hold true with this watch? Considering this is an electro-mechanical hybrid. Can demagnetizing really help?

    Hope to have your opinion before I bring it over to a service center.

    • sweephand says:

      Hi Jay, sorry to hear your watch has got a problem. If it hasn’t been used for a while it may just need a thorough clean and service. I’m not a watch ‘techie’ so I’ll see if I can get some advice from an expert on these watch types who I use for servicing / repair of mine. The balance on these has magnets on it so I would avoid trying to de-magnetize unless the experts advise it! I’ll get back to you as soon as I can, via email rather than here – in the meantime I would avoid running the watch if it is very fast. They run at 36,000 beats per hour anyway, but you don’t want to damage it further. I guess it could be that damage from the leaky battery is causing a problem with electrical contacts.

  5. Douglas Ott says:

    Just Picked up an orange dial 4800031 as pictured above in the second catalog spread. The watch is in exceptional condition and seems 100% original survivor. You can hear the mechanical balance watch ticks like a mech wind. Watch has date function and minute track is yellowish hands dial are mint. Cool find only paid a little over $100. Seems like a steal. Photos to follow

    • sweephand says:

      Hi Douglas, thanks for visiting my blog and sorry for slow reply. Congratulations on what sounds like a great buy of an interesting watch at a very good price 🙂 Looking forward to photos – although you can’t post images directly, you can post a link.


  6. robert says:

    Hi, I recently purchased a Cosmotron with a 7802 movement like the one pictured in the 8X blog. When I received the watch it wasn’t running and the zero function seems to be malfunctioning. The seller has offered to refund but it will cost more to return than I paid for the watch so I was wondering how one goes about removing the back.It appears the solid block on the back spins off but I have no idea how to begin. Any suggestions would be a great help. Great Website. I have a few Hisonics as well so I should be a very frequent visitor.

    • sweephand says:

      Hi Robert, thanks for visiting my blog 🙂 Does your watch have this kind of case?:

      If so it is a ‘monocoque’, i.e. one-piece case – which is why the case back has the small access hole to adjust the balance. To get at the movement the bezel and crystal have to be removed. Great care would be needed to prise the bezel / crystal off safely and without damage to the case and or bezel. I’ve just had a look at mine and there is a small notch in the bezel to help with removal. I presume there must be a small lever that can be accessed once the glass is off to release the crown and stem, so that the movement can then be extracted through the front of the case. Here’s a link to a pic of a King Seiko with similar case – it has the instructions for stem removal stamped on the back:

      I can recommend a great guy in the UK who can service these – let me know if you want his contact information.


  7. trxtr says:

    hello again. a quick question about 7803, as I just got one for myself
    if the movement beat-rate is 36000bph I expect to see a floating seconds hand. but in fact the hand movement ticks are visible and I’d say it makes about 4 beats per second, not 10. How is that possible?
    Also is it ok for this monocoque case to be marked 7803, not 7800? Do I need to pry the bezel up or to turn in clockwise or counterclockwise?

    • sweephand says:

      Hi trxtr, I have noticed that the Cosmotrons’ sweep is not as smooth as a mechanical high beat watch, and there are more noticeable ticks. The 78xx movements are definitely rated at 36,000 bph. It is ok for the monocoque case to be marked 7800. The bezel should be prised upwards, not turned. You need to be careful to avoid damaging the bezel or case. Some people suggest using a plastic card (like a credit card) that has been carefully shaved to give a sharper edge.


      • trxtr says:

        I should say it’s a very strange design choice to slow down the seconds hand. Well, this watch is full of strange design. Thank you again

        • sweephand says:

          I don’t think the design slows it down – I think it is just the action of the balance. If you listen to the movement, and it is running at the correct speed, it should sound something like this:
          [audio src="" /]


          • trxtr says:

            yes it does sound like this. Still, this puzzles me. I’m not an expert in watch inner work, but in most mechanical watches the number of beats per second directly translates to the number of ticks of the seconds hand. I also have Bulova accutron 214 with beautiful floating seconds and I’m surprised to see Citizen forcing the seconds hand to move twice slower then it could.

      • trxtr says:

        hi Stephen,
        sorry to bother you with my experiments but I heed some help. So I’ve tried to take my monocoque cosmotron apart, and removed the bezel (fyi plastic card trick failed for me, as the bezel was to tight), But I have no idea how to interact with the lever to release the stem. I don’t want to do trial and error, fearing I will break it. May be you have an idea. here’s a crude pic
        should I push it downwards or towards center? or pull, maybe? In what position should the crown be at that moment?
        Also, can you give me the reference numbers for the spare glasses and crowns for this model? Thanks again.

        • sweephand says:

          Hi trxtr, no problem about your questions, this is something I’m interested in too 🙂 I’ve taken the bezel / crystal off mine to see what the lever looks like, and now have the same question as you! Normally, the crown is pulled out fully before it is released, so I presume it’s the same on these. But, I have not been able to remove the stem. So I have just emailed a guy who works on these to ask him for his advice, so I hope I can soon let you know what to do. He usually gets back to me quickly so there shouldn’t be too much of a delay – better to wait than damage the watch I think! In the meantime could you let me have the model / case number on yours, so I can try and get the part numbers you are after.


          • trxtr says:

            the dial is marked 7803 790208-Y
            the case is marked
            7803-790090 TA

            • sweephand says:

              Hi trxtr – thanks for the information. I got a reply this morning about the stem release, here’s what I was told:

              “1) Pull crown out to farthest position, that will swing lever out into exposed position
              2) Push down on lever while pulling on the crown / stem”

              Hope that helps and you are able to get the movement out.

              The original part numbers for your watch are:
              Glass: 54-60721
              Crown: 506-3441
              Stem: 065-2140

              Original parts are hard to get – there is a crown for sale at the moment on Yahoo Japan:


              • trxtr says:

                thanks, but it didn’t work for me
                after I pull the crown to the time setting position, the lever doesn’t move much. it remains almost completely under the dial, and I cant force it further. Also I don’t really follow which way is “down”. I tried pressing different directions while pulling on the crown with no results.

              • trxtr says:

                thank you for the hint, so I made a bid on that crown at Yahoo Japan (still no luck taking it out, lol), but have difficulties finding the glass. Does it have to be *precisely this number, or there’s some array of glasses that can fit?

                • sweephand says:

                  Good luck with your bid on the crown. I have searched for a crystal but also with no result I’m afraid. I’m not sure whether you can get a suitable replacement – can you remove the crystal from the bezel? If so you could very carefully measure it and check what profile the edge has, and then see if there is a modern equivalent.


                  • trxtr says:

                    it’s removed from the bezel, no problems with that. The diameter is 30mm or a tiny bit less. There’s an extra metal frame at the glass bottom, I guess it’s to add some space between the glass and the dial. Here’s a pic (the glass lays upside down)

                    • sweephand says:

                      thanks for the pic – I think the metal ring is also there to ensure a tight fit, so it is an important part. The edge of the glass also has to be the right to ensure the bezel fits properly. Is there a watchmaker near you? If so it might be worth taking it to him to see if he knows of an alternative to the original.


  8. Mike says:

    Stephen,do you know a source for cosmotron parts. Thanks Mike

    • sweephand says:

      Hi Mike – parts are difficult to source, so donor movements are often the likeliest way of getting them. What are you looking for? Paul, at Electric Watches (in the UK), is an expert on this type of movement, so I would recommend him if you want someone to look at it, and he may be able to repair as well as carry out a service.


  9. Mark says:

    I recently wrote a review of two early X8 watches on which you might find interesting.

    • sweephand says:

      Hi Mark – thanks for letting me know, had a look at your post. Very interesting. Would you have any objection to me incorporating the information in my article on the X8/Cosmotrons (with credit to you of course)?


      • Mark says:

        Hi Stephen,

        You’re welcome to lift anything that you want. Its great that you maintain such a comprehensive resource here on this interesting family of old watches – thanks.



  10. Stefano says:

    Dear Stephen,
    I am writing to receive an advice or help about my Citizen Cosmotron with a 7803A module.
    The watch runs very precisely if left on a table or in a drawer whereas it starts to lose more that 10 minutes a day (it then slows down) when on my wrist.
    When changing the battery I noticed that the battery holder is kept in place by just 1 screw since the other side holder is missing.
    I thought that could be the problem since the battery might move when the watch is on my wrist.
    However I think that the caseback should be keep the battery well in place.
    can you give me some recommendations to solve the problem?
    Thanks for your kind attention.
    Stefano from Rome

    • sweephand says:

      Hi Stefano, thanks for visiting my blog. Good to hear you have a Cosmotron, I think they are great watches and as yours shows they can run very accurately. I’m afraid I am not a watch repairer so my advice is rather limited when it comes to faults and repairs! Although you may be right that the case back should hold the battery in place it might be best to see if the battery holder can be secured with a second screw first to see if that solves the problem. Have you a local watchmaker who might have a suitable screw? I’ll also see if I can get some advice from a watchmaker who knows about these movements who may have seen the symptoms you have described, and get back to you.


      • Stefano says:

        Dear Stephen,
        thank you for the reply and my frank congrats for your blog and all the information provided!

        • sweephand says:

          You’re welcome Stefano and thank you


        • sweephand says:

          Hi Stefano, I’ve now had some advice from an expert on this type of movement:

          ‘It could be anything really….from a small piece of debris stuck to the balance magnets, to a worn balance pivot. Because the balance needs some up-and-down clearance, it will run happily when on the bench because balance is running in the bottom position with the clearance on the top pivot, but as soon as you begin to move, the balance will move up and down slightly and any debris on magnets might start to interfere with static coil etc.’

          It looks like a service is needed.


  11. ijdod says:

    Hi, what sort of batteries do the 78xx movements take? I find plenty of options for 1.5v, but 1.3v seems to be a bit of a bother.

    • sweephand says:

      Hi thanks for visiting my blog. 1.5v silver oxide, low drain, is fine for the Cosmotrons although the 78xx originally used 1.3v. I use the Renata 301 in mine, so that or an equivalent will be ok. Stephen

      • ijdod says:

        Thanks! I really enjoy reading your blog. On the down side, it may trigger my Watch Acquisition Syndrome 😀

        • sweephand says:

          You’re welcome – once tiggered that syndrome is hard to get rid of! 🙂

          • paul says:

            I found a citizens watch assembeled in Germany model no 2810-9557905A5080362 81-5705 a old 12 jewel japan movement ladies watch any info on

            • sweephand says:

              Hi Paul, thanks for visiting my blog. I’m afraid I can’t help too much since the watch is a relatively modern quartz model, so is much later than my area. The movement is a 2810, as per the case number 2810-9557905. 81-5705 is the model number. The serial number is 5080362, so I would guess it is from 1995.

  12. Pingback: And now for something completely different: the Seiko Elnix Electronic Watch | Adventures in Amateur Watch Fettling

  13. Chris irish says:

    Invaluable source for cosmotrons,just got cosmotron special all working except the hour and minute hand don’t run to 12 ,seconds hand is fine and works as it should.,day date fine as well..
    Thank you very much for the info

    • sweephand says:

      Hi Chris – thanks for visiting my blog, and I’m happy to see that it has been of some use 🙂 Congrats on acquiring the Special Cosmotron, a very nice piece. Stephen

  14. Chu Dat says:

    Hello, can you help me?
    I want to remove stem in my citizen 7084a
    How to do it?

  15. Hello, I have X8 Cosmotron with caption on back “With the Compliments of Citizen watch Co.,LTD Citizen trading Co.,LTD Eiichi Yamada President in June 1970” and blue Cosmotron emblem and number 6-810055 YD on dial. What you can say about this watch? Thank you!

    • sweephand says:

      Hi Alexander, thanks for visiting my blog. I hope you have got enough general information about the X8 Cosmotrons from my blog page. From the dial code, I believe your watch has the 0840 movement inside, so it has a plain dial, with no date complication. Is that correct? Your watch was obviously a presentation piece but it’s not clear whether it was to an employee or maybe it was a complimentary gift to a guest of the company. Eiichi Yamada became president in 1946, so he was president of the company for a long time – until 1981 I think. The inscription clearly dates the watch – are there any other markings on the back? Stephen

      • Thank you so much, Stephen! The opening showed that is 0880 movement with 18,000 bhp. And there are no more any other markings on the back.
        My collection has increased with one more Cosmotron. It’s 4840 movement I think. Clear, colorless Cosmotron emblem and 4840-480730KA on the dial and 4-480341Y and 1 1232358 on the back. What you can say about it? And what means YD and KA on deals? Thank you very much!
        With good wishes, Alexander

  16. skyM says:

    Hello everyone, these are mine. It is a pity that the bracelet is not original.

  17. Marcia Bauer says:

    Hi, I have a Citizen with the number 6100-072910 on the back. I can see no way to get the back off to replace the battery. It belonged to my girlfriends uncle many years ago. Can you tell me anything else about it. Thank you in advance. Al

  18. Aleksej says:

    Be so kind as, prompt how to decipher numbers on old models of hours Citizen Cosmotron.?
    I want to learn date of production.
    4-480121 Y
    Japan 6 480306. Ka
    I ask you, by all means answer me mail.

    • sweephand says:

      Hi Aleksej, thank you for visiting my blog. The first three figures in the serial number (10120584) give the production date, with the year first. The Cosmotrons were only made between the late 1960s and the mid 1970s, so yours was made in January 1971. Stephen

      • alexis2891 says:

        Well Stephen, thanks. I correctly understand that the first figure, is the last figure of year.Knowing that Cosmotron was issued during the period from 1966 to 1972. It becomes clear what 1 is 1971.And is 01 the first month, January.But what mean the subsequent figures?I believed that the 2nd is number of week, or the 20th.But then becomes not clear that means 0384, or 384.I could assume, on association in cipher on production of engines that time, for example 20:38 is specified further.Then there is figure 4. Further, from all these designations (four number the code) it is possible to gather still any interesting information?And what is ciphered in number on the dial?I suggest to consider a photo also. Ach da Stephen if to you interestingly, tomorrow, I can offer you a photo of my hours of the Russian production of Chayka using technology the Quartz resonator too.And thank you. You have unusually deep, most interesting article!21:16, 3 апреля 2019 г., “Sweephand’s Vintage Citizen Watch Blog” <>:

        sweephand commented: “Hi Aleksej, thank you for visiting my blog. The first three figures in the serial number (10120584) give the production date, with the year first. The Cosmotrons were only made between the late 1960s and the mid 1970s, so yours was made in January 1971. S”

        • sweephand says:

          I believe the other numbers in the serial number are related to the number produced over the month – so yours was the 20,584th watch made that month. I don’t know whether this was just this model or perhaps it was the total number of Cosmotrons in that production line. As another example, I have a watch with serial number 3100010, so that would not fit the idea that the week number is included – rather it means it was the 10th watch made in October 1973. The number on the dial – the dial code – is the part number for that particular dial. Dial codes often start with ‘6-‘.

          I would be interested to see a photo of the Chayka quartz watch – I will email you so you can send it to me, since you can’t post a pic here. Or you can post a link to pics if you prefer. Stephen

  19. skyM says:

    I have a problem. How to distinguish between models 0840 and 0880. On the back cover, you can understand which of these mechanisms is installed?

    • sweephand says:

      Hi, I’m not sure you can easily tell the difference. The 0880 runs at 18,000 beats per hour, whilst the 0840 runs at 21,600, so that might be a way of checking. Stephen

      • skyM says:

        Yes, yes, that’s understandable. But by the external design of the watch, I can understand where which ones? According to information on case back? Or case?

        • sweephand says:

          I’m sorry, I don’t know if they use a specific type of case number for each variant. Sometimes the movement is the first part of the dial code (small printed number at the 6 o’clock marker), so that may do it. Stephen

  20. Keith says:

    Do you need to oil the movement? I have a few Cosmotron which is still running accurate.

    • sweephand says:

      Hi Keith, thanks for visiting my blog. I’m not a watchmaker so I can’t give technical advice I’m afraid, but I know that the mechanical parts should be cleaned and oiled like a typical mechanical movement. The 78xx models have an unusual date/day change system, and the lever that moves to change from day to date should not be oiled, but it is marked clearly on the lever. You can see this on my X8 Cosmotron reference page:

  21. Yuri says:

    From a japanese watches’ lover – you are doing god’s work here.

    Never even heard of this lineup. Glorious!

    • sweephand says:

      Hi Yuri – thanks for visiting my blog and for your kind comment. Not everyone knows about the X8 Cosmotrons, but when they do find them, they usually like them! 🙂 Stephen

  22. Nigel Pate says:

    good blog ive just bought a cosmotron from 1972 my birth year ive dated it frrom your info on 36000bpm. Thanks.

  23. Mark says:

    Hello Stephen,
    i was wondering if you have access to some service manuals for the 78 and/or 08 movements. i seem to be having problems with the electronic module of my 78 cosmotron and am wondering if the service manual might have something useful.

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