I've got an older CH 2605 that my son has banged to hell.
I just put a new battery in it and it seems to be working fine. At least it's been telling time to the second for several hours so far.
The issue is that the chrono pushers don't seem to work. The top pusher seems to stop and start the timer most of the time. The bottom pusher (I'm guessing the reset, I don't have the instructions) mostly doesn't do anything. If it does the bottom sub-dial will spin around very quickly for several seconds, then stop.
It has a tach around the outer bezel so I suppose the big second hand is supposed to play nice with the chrono, but never reacts to any pushes.
Is there anything that I can do to maybe get them to work. I'm not willing to put any real money into it. I'll just use it as a daily banger at work.