Service + Repair: Tissot SeaStar Automatic calibre 2770

IMG_0373This is Paul’s Tissot, and it’s very much a child of its time. The calibre 2770 was built between 1976 and 1979.

It’s got a TV style dial, and a fairly unique case.

The two parts of the case are held together by two metal strips, that are pushed into grooves that are both in the back and front part.

On this movement, Tissot heavily used plastic components. The whole movement looks like it was a cost-cutting exercise from start to finish. I count 10 jewels, so only the balance and escape wheel have jewels, and there is as much plastic as you can get into a movement. Only the top side of the pallet fork is jewelled, thus the 10 jewels, and not 11.
The case back is solid.
The rotor is held in place by a circlips, and has a wire spring ratchet that allows the rotor to wind the mainspring in one direction.
Just in case you haven’t seen enough plastic yet 😉
Yes, the crown wheel bridge is plastic, too.
The bottom plate.
Almost everything taken apart.
I can’t get hold of a new mainspring, but the old one doesn’t look too bad, so I will use it again.
I start putting the movement together.

When I put the gear train together, I notice that the fourth wheel wobbles. And there is a good reason for that – the pivot hole in the plate is completely worn out, and I need a new plate. Thanks to eBay, I find a complete movement, which has a good wheel bridge.

The same photo of the new wheel bridge – perfectly round.


With the replacement wheel brigdge in place, I can start to put the movement back together. Notice that no money was wasted on the pallet bridge, either.IMG_0655

The balance is back in, and the movement starts ticking. I don’t get a decent image on the timegrapher, and I notice that the hairspring touches the outer stud when moving, so I have to reshape it a bit.IMG_0657

That looks much better, and all I will ever get out of this movement.IMG_0658

Time to start assembling the bottom plate.IMG_0661

Nevertheless, the movement has a quick-set date function!IMG_0663

The winding stem is split, as the case back can’t be opened to remove the winding stem.IMG_0664

Back in its case and ticking.IMG_0665

A true child of its time.

12 thoughts on “Service + Repair: Tissot SeaStar Automatic calibre 2770

  1. Hi,
    My hobby is repair and renew the old watches. I alway bid watches on Ebay. I have a same Tissot 2770 watch but I don’t know how to remove the movement from the case. Can you tell me how to remove it? Does all of this model is two piece stem?
    Thank you.

  2. Hello,

    I have a Tissot T12 Seastar with a similar case construction but with a form factor “with an edge”. I have been trying to find a replacement for it and had a most friendly correspondance with Tissot historian/archivist. Unfortunately only thing that has been clarified is the movement (Tissot 794 automatic 21 jewels with day & date). The model itself seems so rare that not even google can’t find images. Currently there are only my images that I have posted to Could I post some documentation to you in case that you might have seen a similar case? Perhaps you have seen this particular crystal somewhere or even have one?

    • Feel free to send over some photos. But if Tissot can’t help you with a crystal, it’s quite unlikely that anybody else can.
      Another option is a watch glass cutter, and I can point you in the right direction.


      • If it is the thread I am thinking of then the watch construction – and crystal design – is very similar to that of my Constellation where the step on the crystal forms part of the case seal… very difficult to fashion one I think.

        I am still hopeful 3D printers will be of use in situations like this – maybe not to print the actual visual bit of the crystal, but maybe to print the shoulder and step a cut / sourced crystal could be bonded to.

          • C. is right, the crystal is actually in a condition that can and has been finesanded and under polishing (by yours truly). The welding sparks that had been burned on the crystal actually were not as deep as it first seemed. The bigger issue are two cracks that I found from opposite corners of the “collar/lip” on the outer rim of the crystal.
            I managed to solidify these quite nicely with a good instant glue. I have compared different kinds of moldable plastics, and the best and cost-effcient Plan B for future crystal replacement seems to be a silicone casting mold from the original crystal and making of several pieces with different mix-ratios and materials. Best option right now seems to be a casting polyester, which is hard holds dimensions and doesn’t turn yellow on UV.
            I don’t think that RPT will produce decent enough pieces for a while, and the materials have issues.
            We’ll see what happens when the time has come to make the molds and first castings.

  3. Odd case construction, but still damn cool! What is the purpose of the rivet-like thing on the back of it?

    Could the wheel bridge have been broached out and and a new bush fitted? I know this is a common enough operation on old clocks, but I guess it is a more complicated prospect on something watch sized…

    • I don’t have a clue what the plug thing on the watch back is for! As a guess, you might be able to adjust the beat rate when that’s removed …

      Re-bushing – in principle, yes. But it’s cheaper to buy another one. On this particular bridge, almost impossible, as the tube for the oscillating weight is above the worn bush, so I don’t think you would have much of a chance fixing that with less than a full day’s work.

      • I’ve seen that plug on a number of different monocoque (is that the right word?) cases in the Tissot Seastar7 and and Sideral ranges from the 70s where you have to access the movement through the crystal and dial. In this case it seems to line up with the advance/retard lever, so presumably for regulating the watch after casing.

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