Epos Triple Date Moon Phase Chronograph, Valjoux 7751 Movement, Minor Adjustment

I don't do much tinkering with watches anymore since I have Familial (or Essential) Tremor. As the name implies, it causes shaky hands and is passed down from parent to child. Lucky me. Anyway, this Epos watch was bought in 1999 (for a whopping sum at the time of $697) after we'd paid off our house loan. It was a time to celebrate and my wife and I each decided to splurge on something nice. This is what I chose to buy. It had been having minute-counter issues for a number of years. When the chronograph was started, the central seconds hand would go round-and-round as it should but the minute counter would haphazardly either count or not count up the minutes (and since the hour counter was tied to the minute counter, its movement was also intermittent).

I didn't wear the watch much lately because I'd gotten other nicer watches over the years but I pulled the Epos out a few days ago to wear it. That's when I decided to try and fix the problem. It is not a small task to delve into an automatic chronograph movement, and it is compounded immensely by both shaky hands and the fact that this chronograph is additionally complicated with a 24-hour pointer, triple-date (day/date/month) functions and moon phase. I'd watched several videos on YouTube prior to taking the plunge, so I figured I knew pretty much what the problem was and how deep into the watch's bowels I had to go.

The watch has a fairly ubiquitous Swiss ETA (or Valjoux) 7751 movement. The 7751 is a step up from the popular 7750, which is a three-register chronograph used in most automatic chronograph watches these days. In addition to the 7750's seconds/minutes/hours chronograph functions, the 7751 has a 24-hour hand, moon phase dial, day of the week, pointer date, and month indications. Yep, a lot going on inside one of these movements. Fortunately all of the additional function mechanics are on the dial side of the movement, so working on the back side of the movement is not much different than working on a "standard" 7750.

In the above photo, the automatic winding weight came off first, then the winding bridge. After that the oscillating pinion lever and spring came off, along with the reset hammer lever and hammer spring. This next photo below shows the extent of disassembly. It's not too horrible but it is daunting to think about getting it all back together with my hand condition.

Zooming in to the above photo (shown below), the red line shows the spring that needs to be tweaked outward a little, to mesh better with the minute counter idler gear teeth shown in green. The way it works is the large wheel in the center of the photo has the "red" spring attached to it. When the "red" spring makes its way to the small "green" gear, the spring is supposed to push the small gear one tooth over, which counts up one minute. If the spring has too little force on the gear, the gear won't turn one notch.

The yellow arrow shows direction of rotation of the center seconds wheel that the spring in red is attached to. I reached through the wheel with some very fine tweezers in an attempt to bend the spring outward ever so slightly. If I went too far or too little, it would not operate properly. Problem is, in order to test if the tweak works or not, the entire mess has to be put back together. (Side note, the blue circled item below is the oscillating pinion, which will give me headaches later.)

This next photo is one I grabbed from the net showing an inverted center seconds wheel with the small spring that needed tweaking on my movement.

This next photo is after tweaking the spring and starting to put things back together. I had to wrestle with getting the oscillating pinion's (yellow arrow) pivot back in place in the pinion lever's (red outline) pivot hole probably 50 times because the thing kept getting bumped out of place. Sometimes only the top pivot needed to be redone, but other times the lower pivot would also jump out of its jewel, and that one was majorly difficult to get back in place. Sigh. The oscillating pinion lever is in red, and the reset hammer is pointed out by the green arrow. Both those items are just laying on the movement at this point in time (engaged to their respective pivot points) so nearly every time I placed the winding bridge on top of them, they'd get bumped out of position and I would have to start over.

The winding bridge was a chore in itself, in addition to bumping the previously-mentioned parts out of place. The bridge contains several wheel jewels and pivot holes, along with a one-way clutch, so it was difficult getting all the pinions lined up to their respective holes while trying to keep the pinion lever and reset hammer in place. After the bridge was finally secured with screws, I went to put in the oscillating pinion lever spring. It didn't want to cooperate, and at one point during the struggle it pinged off into space. Fortunately, not too far. It could have gone into a black hole but I did find it. It's in the photo below, as you can plainly see.....

Yes, it's there.... You can't see it? Ok, below is a zoomed-in shot of it, right in the middle of the photo. Yes, it's that little wispy wire thingy almost underneath the shell casings in the plastic bag. God altered physics around that thing in mid-flight and kept it from going further than maybe 10 inches from the movement. He also kept a couple of screws on top of the bench so I could find them after they took their little excursions from the grip of the tweezers.

I didn't take a photo of the completed movement but below is an old photo of the movement from 20-some years ago. It looks basically the same today, and the watch is still on the original Epos strap.

I wound up the watch and started the chronograph at 4:30 (photo below). It's now 5:51 and the minute and hour counters have counted up an hour and 21 minutes. Yay, I would call that a success. The job took about four hours.

The below video is just messing around with my phone's camera. It is a super-slo-mo of the balance wheel ticking away.

The below screenshot is of an app I have on my phone. It's pretty cool. It shows the beats per hour of a mechanical watch movement, the plus/minus seconds per day gain/loss, and the balance wheel beat error. I bought this watch in 1999 so I'm really surprised the movement is keeping time to +/- zero seconds per day with no maintenance having been done to it for 24 years. Well, no maintenance other than the adjustment I did today. I guess what's most surprising is the fact that the watch even runs after I've had my grubby little mitts in it. It's a far cry from working on tractors.

Postscript: Oh, and that original Epos watch strap I mentioned earlier? It broke about a week after I originally wrote this blog post. I caught the watch on a door frame while carrying some Christmas decorations. Fortunately the watch didn't fall. It stayed inside my shirt sleeve until I could retrieve it after putting down the decorations.

Post-postscript: I have a Hamilton chronograph with pretty much the same movement as the Epos, except it doesn't have all the extra moon phase/triple date/24-hour indicator paraphernalia. It's movement is the ubiquitous 7750. I took a super-slo-mo video of the center seconds hand resetting to zero. To the naked eye it looks like the hand snaps back to zero instantaneously, but in real life it overshoots the mark and oscillates several times before stopping at zero.