Having finished the service of the Tissot Seastar, a fairly simple manually wound movement, I move onto the more involved ETA 7750 chronograph. The watch was passed to me by a good friend of mine, apparently the watch is losing time and stopping randomly – a good sign its time for a service.
The ETA 7750 is used in all different brands of watches, but more often than not, under the guise of a different calibre number so it can be passed off as their own, often they make just a simple change such as using their own rotor. Theres a reason its used so prevalently, its robust, easy to work with, and brands can modify it quite easily to suit their requirements.
Ive taken the back off and removed the rotor to give you the first glimpse of the movement. The overall condition of the movement is very good, the oil is just dried up and it needs servicing. Also notice the gunk round by the lugs, the case needs a clean as badly as the movement!
Once the movement has been removed from the case, I ready the hands for removal. Theres a few little marks on the hands, suggesting they’ve been off before. Chrono hands can be a pain to take off, especially the centre seconds recorder hand. It has to be fitted very tightly so it doesnt move when the chrono is reset, Breitling are notorious for it. If you dont know what you’re doing its very easy to end up damaging the hands in the removal process.
Once the dial and hands have been removed the date work is visible. Notice the way this is set up, its very important and actually shows you why you shouldn’t change the date via the quick date function between 9pm and 3am. At ‘5’ on the date disc you can see where the brass slow date change wheel will engage with the date disc, then look to ’29’ on the date disc and notice the silver star shaped wheel adjacent to it – thats the quick change wheel. If you set the date using quick date i.e. engage the star wheel, whilst the slow date change is engaged, i.e. the brass wheel, it will more than likely damage the movement as they fight against each other – so dont do it please 🙂
Date works removed and im ready to remove the next bridge.
Next is the motion works and the hour recording part of the chronograph.
Other than the keyless works, the dial side is stripped.
I flip the movement over and start work on the otherside.
The picture below is a part called the oscillating pinion, it is the component that links the watch part of the movement to the chronograph part of the movement, you can also see black dirty oil on part of the pinion – that will be cleaned off in the cleaning machine. The 20 pence piece is to give you an idea on the size of the part.
The chronograph parts to the movement have all been stripped down, what remains is the usual parts you would find in any watch. Some old oil and dirt is visible.
A good tip I learnt early on in my career is what to do with screws that are similar – put them back in place once the particular component has been removed. The 2 screws in the picture below are very similar, and I dont want to mix them up. In some cases a screw fitted in the wrong place will stop a movement dead, so its important everything goes back where it should.
This side is stripped, next ill flip back over to remove the keyless and put the whole thing through the cleaning machine to remove all the old dirty oils and get everything looking shiny new again.
Everything stripped down. Ive checked all parts as ive removed them for any sign of wear or damage, if I find any the part will be replaced. At this point, with nothing else on the manipulate, I will check the hairspring for flatness and concentricity. Any adjustments are made before the movement goes through the cleaner, after its been through the cleaner its imperative the movement remains completely clean, thats easier to do if everything that needs to be done is carried out before cleaning. Once cleaned if the watchmaker has done their job properly, it should just be a case of putting the movement back together and oiling as they go.
First section of the watch to go back in after cleaning is the keyless works.
Train and train bridge back on, once I get the crown wheel and ratchet wheel back in place, I can wind the movement and get it running again. At this point, before I put any chronograph parts on, ill check everything on the timing machine. Theres nothing more frustrating then building the entire watch up, only to realise theres a problem, and having to strip it right back down again!
Ive oiled it, checked it, and all seems good, so I forge ahead with the rest of the movement. Once you’ve done a few 7750’s they become a breeze to work on, have minimal problems, and go together very nicely.
Chronograph layers gradually being fitted.
Other than the rotor, this side is complete.
Motion works being refitted.
Date work is back on and the watch is nearly complete.
After the dial and hands are back on ill turn my attention to the case, which is filthy if you remember?! So I give that a good clean and replace the seals to make sure its water resistant.
Final checks on the timing machine, and its running very well. Only 1 position shown in the picture, but I check 5 other positions to ensure theres no timekeeping issues in any position.
Before the watch goes onto the testing stage of its journey, I will test it for water resistance.
The final stage is testing to ensure it functions as it should and passes all the tests according to the manufacturers specifications. These include power reserve, time keeping and automatic winding tests.
After the tests are completed, the service of this Tag Heuer Carrera is finished and it can be returned to its rightful owner. I know for a fact he will be pretty pleased as he’s told me regularly how much he’s hated not having a watch to wear!
Thanks for reading.
The Watch Professional.