Tag Heuer 7750 movement (chronograph wheel)

[AP1875]

I was offered a Tag Cal 16 at a good price so I bought it to practice on. All functions were working correctly.

I have serviced a 7750 previously about 18 months ago, took me a while but no issues.

I’ve finished assembling the chronograph, installed the hammer and clutch springs however when the pinion is pressed against the chronograph wheel the chronograph does not turn. Everything locks up which causes the balance to stop.

The chronograph wheel does not spin freely with the chronograph bridge installed when I try to turn it with a plexi stick. It feels rough and tight. The reverser and minute chronograph wheel turn freely. The jewel is still in place on the chronograph bridge.

I’ve taken the chronograph apart and rebuilt it twice, tried 2 chronograph wheels, doesn’t seem like there’s much I can adjust.

Hit a bit of brick wall. Any advice on further checks welcome please.
 

 

 

 

[nickelsilver]

You're in the stop position there, so the brake should be pressing against the side of the chrono runner wheel. Put it in the run position, make sure the rocking pinion is correctly in it's hole in the mainplate, and in its bridge (and right-side-up- little teeth to the chrono runner), and that the friction spring is correctly in position under the chrono runner. There, with the rocking pinion pulled away, the chrono runner should turn freely.

[AP1875]

Hi @nickelsilver this is after I have tried to run the chronograph, I have stopped it and removed the clutch spring, hammer spring and removed the chronograph bridge for reference.

I have rebuilt it this evening, when I press start after 10 seconds or so the balance stops. This is because the pinion is pressed against the chronograph wheel but the chronograph wheel won’t move freely.

I press reset the pinion moves away and the balance runs. Pinion orientation is correct.