After having serviced 3 of this movement, without much technical information available online (there's a YouTube video), I found 2 design decisions that made this a tricky movement to reassemble: the setting wheel lever complete and the second jumper (names borrowed from similar parts in a 3863).

The setting lever complete features a rocking set of wheels which shifts between left and right when quick setting day/date. The wheel would be confined by the + shape opening on the flat piece of yoke spring such that the wheel doesn't move in normal/time setting position.

The original paper 《低刻音薄型長寿命掛時計用ムーブメントの開発》—馬場康治 describes the working principle of this movement. It's fun to read. AI can OCR and translate it for you if you can't read Japanese. It turned out the smooth second hand movement is a happy side-effect of the original intention to develop a silent and long battery life clock movement.

Honestly, readers interested in how a 5S21 movement works can simply read the above paper and maybe the technical guide of 5S21 and that'd have been sufficient. Here, I am going to inspect into an example of 5S21 I received that would give us more insight into the mechanism, as with many other posts on this site, when things don't go as smooth (heh) as they should.

This is because the date/day driving "finger" would by those times be leaning against the date/day wheel teeth. Should a careless watch owner make use of the quickset function at that point, the "finger" would be subjected to force exerted by the owner's turning of the crown, and thus, either the quickset or the date/day driving wheel would give in and break (or slip, imparting tiny damage that contributes to future breakage).

In Seiko 5606, the quickset would usually give in first as the plastic quickset wheel has a thinner loop around its post compared to the plastic day driving finger, not to mention the metal date driving wheel. This gives rise to the common issue of defective quickset on vintage 5606s.

I PPAP'ed a pair of 5606-7000 to put the gold-tone chapter ring, dial and movement onto a steel case.

It's not like nobody has ever done that.

I have always thought AGS is a scam. The latest iteration of that is Solar. Whether the generation system is by kinetic generator, or by photoelectric cell, they both rely on a rechargeable battery that gradually loses its ability to keep charge, and eventually the watch stops running.

Moreover, the owner needs to keep the battery topped up all the time, otherwise the battery overall lifespan will be shortened. And while the watch is kept running, whether the owner wears it or not, its gear will continue to wear.

Most people who take themselves seriously wouldn't have subjected themselves to this excessively artistic subject.

To those who took themselves seriously, this is the gist of PPAP:

The cup has an opening at the bottom to expose anode (-ve end) and open top to expose the cathode (+ve end) of the battery, so there are only 2 possible places where the battery can touch: the negative terminal and the conducting spring on the battery cap.

Without the insulation cup, the battery will wobble in the battery compartment of this movement within a case where the anode of the battery may touch the other parts of the base-plate causing a short.

At first, all that I did was shopping for compatible parts online and assemble them into a watch — what people nowadays call "AIY" (assemble it yourself).

It didn't take long before it gets boring. Despite the multitude of choices the combination that I liked quickly ran out, kind of like the shows I like on online streaming platforms.

This is an innocent looking quartz with brutalist numerals. I got it because I liked the angled sides of its lugs.

That watch runs with a fresh battery. The movement itself looks clean too.

That was the beginning of a traumatic experience.

The Timex arrived not running with a fresh battery. A closer inspection revealed an overbanked balance wheel, where the impulse pin went over the wrong side of the pallet fork causing the balance to be stuck.

The mainspring of a manual and automatic watch work differently.

Lip of a manual watch mainspring hooks onto a notch on the barrel wall which holds it in place as user winds the watch.

The 8229-6040 on the right above ("the old one" hereinafter) is one of the junk that came alongside the two "bait" watches: a Seiko Elnix and a Seiko Crown that I wanted.

The other junk was a 5933-7020 that I wrote about earlier.

There are 2 brands of sweep seconds quartz movements that are obtainable freshly new nowadays: TMI VH31 and Sunon SP25/28/68 series.

The Reddit r/SeikoMods community where poor folks show off their first/second/third/nth build to serve up their confirmation bias had revealed a trend of using the VH31 quartz sweep second movement to replace the automatic NH3X series of movements, even so far as to creating a set of VH31 movement rings to fit them onto NH3X-compatible watch cases, in order to save money on the movements.

My inspiration came from the two informative websites Ostalgie-Ruhla Watches of the GDR and Watches of the USSR listing watches made by various factories in the Soviet Union—not because of the recent trend of neo-Sovietism but more because they are printed dials with some unique designs.

For example this one is copied from a Slava featuring a California dial. I chucked the Island boys trio in there and stuff the thing into a NH36 build.

After months of trial and error with different materials and techniques, I think I have finally got somewhere good enough.

This Baoshihua has a shot dial and some platings on its case has worn off.

I got this from a suspicious looking job lot which I placed a bid either late at night or right after work. A lot of warning signs had been missed despite the detailed pictures and relatively low competing bids.

Well, now it's on my lap I might as well try, for the experience at least.

This 3863-8020 with its blue coarse grain dial design attracted me to bid on a job lot of quartz watches in questionable conditions.

Of course this didn't turn out well.

These dual timezone watches interest me because I work with people in a different timezone.

Just a fun concept I thought of when I saw one, what if I join two ST5 each running on their own timezones.

Got this Seiko 3302-8080 from the same job lot as the 0843-5010 and 8221-5000. I am quite surprised by how much it's possible to save from a job lot.

This 3302-8080 is an electronic watch that was quickly swept away by the tsunami of quartz watch into obscurity in the early 1970s.

I received the 8229-703B from a job lot, whereas 8223-500A was from a separate order.

Both had the same issue: with a fresh battery the second hand twitches but doesn't run, a typical sign of dirty wheels.

This is one of the odd shape watch case where NOS replacement crystal is unobtainium and I suspect any donor crystal wouldn't survive the crystal press either.

I will skip my pathetic attempt with hand-sanding a acrylic plate, which fits on but won't shield the dial from dust and moisture.

After the first Seiko quartz has been introduced, for a couple of years quartz watches were branded as luxurious and superior alternatives to traditional mechanical watches.

This means quartz like this Seiko 0922-8000 would use the same case as a premium mechanical King Seiko with slightly difference in dial and hands design.

The snowflake (?) texture was probably added by another watchmaker after the watch was bought.

Edit (2024-11-11): I did see an 0842-5010 having the same finishing on online auction, yet searching for images of 0843-5010 all showed a flat surface instead of the textured one—does that mean this is a frankenwatch made of 0842-5010 case and 0843-5010 innard?