Seiko Instruments (SII) Caliber VD77A Watch Movement

Manufacturer	Hattori aka Seiko Instruments Inc. (SII)
Caliber Number	VD77, VD77A
Type	Quartz
Lignes	10.5”’
Diameter	23.7mm
Casing Diameter	23.3mm
Thickness	3.45mm
Battery Cell	377 (SR626SW)
Battery Life	~3 years
Frequency	32,768 Hz
Quartz Type	Tuning fork type quartz crystal
Stem	0351 177 (351177) / tap 10
Hand Sizes	1.20mm / 0.70mm / 0.20mm x 2
Jewels	0
Driving System	Step motor
Hacking?	Yes
Anti-Magnetic	> 1600 A/m
Functions	Central hours; central minutes; small seconds subdial at 6:00; 24 hour indicator (also used as a day/night indicator) at 12:00
Country of Manufacture	Japan
Known Models	Android/Aragon Ultra Mini (Too many to list, please add your watch to the comments below…)

The Seiko Instruments (SII) caliber VD77A is a quartz watch movement with 0 jewels. Seiko refers to this family of movements as the “VD7 Multi-eye” series. This caliber has been around since at least March 2016, as that is the date on available technical documents.

Some of the topics covered in this caliber listing:

Accuracy:

SII/TMI claims the caliber VD77A has an accuracy rating of less than +/- 20 per month when the watch is operating in the normal temperature range from -5 degrees C to +/- 50 degrees C.

Time Setting:

To set the time on the SII caliber VD77, simply pull the crown out one click. This movement only has time setting mode, so one click is all you can do. Set the hands forwards or backwards. With the crown pulled out on click in time setting mode, the seconds hand will hack aka stop. Press the crown back in when the desired time is displayed on the dial. The 24 hour subdial at 12:00 cannot be independently set, as this indicator follows the main central hour hand.

Battery Replacement:

A new battery in the SII caliber VD77A should last approximately 3 years. If you need to change the battery, it is possible to DIY. The battery number is 377 (DR626SW).

Crown/Stem Removal:

Look for the arrow with “Push” written beside it. Above this text is a tab with a small indentation. It is only in clear view when the crown is in the correct position, so there is no need to worry about which position to put the crown in when pressing the detent button/tab. Using your tweezers or a toothpick, gently push down the tab/lever while pulling out the stem.