Digital Rebuild: Casio DW-400, Module 905

In 1990, Casio introduced the DW series of digital watches.  There were several models in this series, most notably the DW-4100 Surfing Timer edition.  Watches in this series featured early, and more sleek, derivatives of the soon-to-be-famous Casio G-Shock series, replete with tachy meters and multiple other functions that seem antiquated by today’s smart phone standards (e.g., pre-set alarms).

Enter my old DW-400 from my beach days, bestowed to me by my father 15 years ago when his original 1990 battery went dead.  I always thought it was a pretty cool-looking watch.  Put it this way, Jean-Claude “The Muscles from Brussels” Van Damme sported one in Timecop (“For once, Van Damme’s accent is easier to understand than the plot” wrote Richard Harrington of the Washington Post), need I say more?!

I replaced the battery and wore it religiously for the next 4 or 5 years, retiring it once the battery went dead again.  Recently, though, I got fed up with having to pull my phone out of my pocket every time I needed a time update, so I decided to reactive my Casio for everyday use.  I had no idea what I was in for…

What I started with:

In August of 2011, I started with the original watch: a Casio DW 400, Module 905 – Tachy Meter Edition.  The watch itself was still in pretty good condition, although years of use had rendered the bezel (and, thus, the tachy meter) cosmetic only as it was frozen to the casing.  The crystal display was scratched severely in a few places as well.  Despite these blemishes, I replaced the battery and it worked…on and off.  Having to continually adjust the battery and take my chances that it was actually telling the right time started to get annoying, so I fired up Google and eBay and started looking into replacement options.

What I found:

Well, my knowledge of early 90’s era Casios was certainly limited before I dove into this project.  In my research, I stumbled across the aforementioned DW-4100 (which, by my estimation, is impossible to find) as well as an obscure “sister” to the Tachy Meter edition of the 400 dubbed Sky Walker.  The Sky Walker is identical to the Tachy Meter in every aspect but two: 1) instead of a hardened black resin shell, it features a hardened silver resin shell – a small but significant difference and 2) instead of “tachy meter” across the top of the face, it reads “sky walker.”  If one of these were obtained and presented in the right way, it could be worn under all circumstances, not just for everyday use – it looks that nice.

Enthused by this information, but not holding my breath, I began an eBay search for a replacement 905 module (the actual watch component that fits inside the DW-400 shell).  This took no time at all.  For $50 (including shipping), I successfully found a complete, fully functional Tachy Meter edition that had been obtained through an estate sale in Tennessee.  The watch itself was in the same condition as mine – scratches, obvious signs of use, etc. – but the module worked and, at present, seems not to suffer from the same symptoms of age that my old one does.

What else I found:

In addition to finding a fully functional module, I was able to procure a brand new, never-been-used Sky Walker casing from a source in South Korea over eBay for $30.  This was a steal and had originally been listed on eBay for $80 – I was shocked that he dropped his price more than 60% after only one unsuccessful listing.  Finding this shell, especially in pristine factory condition, is, seriously, almost unfathomable.  To put it in perspective; this guy had this piece of equipment – fragile, useless without the other components, etc. – sitting around for 22 years in absolutely brand new condition.  I’ve seen used Sky Walkers selling on less publicized trading sites for well over $400.  That’s the beauty of eBay – sometimes people just don’t know what they have and there isn’t an Antiques Roadshow appraiser within two continents to tell them.

Next steps:

Finding the new, silver shell raised the ante.  This had become a rebuild project of the highest order – this was going to be a nice looking watch once everything came together, so it needed a band as unique as the watch.  After looking for weeks, I finally came across Maratac’s website.  They make military-style, nylon watch bands in all sorts of gauges and types.  In choosing a band, I figured that 1) I won’t be diving (at least not to 200 meters) any time soon, and 2) while I fly a lot and get a kick out of messing around with the tachy meter I won’t actually be piloting any aircraft in the imminent future, so I chose the simplest option I could find.  The simplest option was the $16 MI-6 band (below).  Even in simple form, Maratac makes a super-sturdy strap that is built to last, goes with everything and looks nice.

Final product:

With a new battery, I popped the new, working module into place inside the new shell, secured it with some putty (I had bent both of the old battery fasteners out of shape), sealed the steel-plate back to the shell and weaved the new strap on.

With the replacement batteries, total cost for the project came to about $105 – a steal compared to what a new Sky Walker – if I’d been lucky enough to find one – would go for.  Not to mention, with all the twists and turns involved in putting this sucker together myself, I feel like it was some of the best money I’ve ever spent (all of which was accumulated from selling old stuff on eBay, I might add…).

Mrs. Cupcake keeps telling me that when I get into something, I really get into it.  I honestly have no idea what she’s talking about.

The Smoking Cupcake, January 2012


13 responses to “Digital Rebuild: Casio DW-400, Module 905

  1. when rebuilding the watch what part activated the alarm on the inside of the watch…. the reason for asking is that I have the same watch but the alarm does not work….thank you….

  2. Hi, I repaired mine just 5 minutes ago.
    Mine had a missing button and didn’t play any sound.
    I bought a very used case, I took from it the missing button, then from another watch the spring to play sound and I put it in the hole near the battery. Now it plays.

  3. There is a tiny spring that needs to be placed into the back of the watch. The ‘beeper’ is actually on the back of the watch (the part you remove to replace the battery) the spring connects the main watch to this ‘beeper’. There are a few videos on YouTube the show this. These spring can get lost when someone replaces the battery and does not know it is there. I thought mine would be missing, but it was there just needed taking out and placing back in.

  4. Hello cupcake,
    i just got me a casio dw 400 nos ,its a real beauty, and now i’ve got a question abaout the watch.
    Hope u still got yours. What im missing though , is a backlight. Is it normal for this watch or is mine just broken. I have a lot of vintage Casios, and they all have light in some kind of form but this one doesn’t seem to have one. Is this correct?
    Hope you can help me.

    Best regards
    Frank Schroth

  5. Frank,
    To my knowledge this model did not come with a back light – at least I don’t recall ever having one. I also see no indicator on the watch face that says “light” where is normally would (on perimeter near buttons). Hope this helps!


  6. Hi,
    Can you tell me which battery fits and what hole the spring fits just found the watch which I have had since new from being a boy, I couldn’t find the video to place the spring.

    Thanks Brian

    • Hi Brian,
      I forgot to mention the gold the spring goes in. There are two holes am the lower left corner of the battery compartment. One says DC next to it and one has no writing. The one with no writing is for the sound spring.


  7. Hi Brian,
    I have my DW 400 and it came with a new battery. So just for you, I opened it to look up the battery size. It was a real pain in the a… to close it again, so be careful not to loose the sound spring like I did. 😦 These suckers are hard to find on a dark carpet floor! 😉
    Well , it’s a Maxwell CR 1616 size battery.
    Oh, and don’t forget to push the little dc hole with a needle! Otherwise you won’t have any sound!
    Hope I could be of help!


  8. Cheers folks

  9. I am looking to buy a Casio dw400 sky walker.

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