I just received my U-Boat Flightdeck 50mm 2 days ago. At first I did not want to use the chronograph because of all the horror stories I have read on the forums. But I thought I would give it a try.... Very, very, very hard to press.... In fact, I cannot press hard enough to start the chrono. After a few trials I come to the conclusion that my 7750 does not work properly. 
Looking on the forum, I have found some very useful info:
http://www.eta.ch/swisslab/7750/7750
I have noticed that the Operating Arm (Pink) was not going under the cam (light blue) as it should. I was kind of sitting to high.
After many trial with the watch in different angle, I could not get it to work. So I wrote to my dealer and he proposed to fully wind the watch (40 turns ) and to try to press harder. Knowing that the 7750 does not like to be manually winded, I went very smoothly. But still the same. The operating arm hits the cam to high and blocks.
Since I am hard headed, I was convinced that my theory was right! I started to shop for a tool to open my 50 mm screw cover and I discovered the "Rubber Ball Trick". My Son had just what I needed
Took 30 seconds to open the case and 10 second to notice that the screw retaining the operating arm was loose, causing it to be sitting to high and contacting the wrong part of the cam. 5 Minutes later I have a functional chrono very smooth to start and stop!!
Now can I call myself a Watch smith?
Looking on the forum, I have found some very useful info:
http://www.eta.ch/swisslab/7750/7750
I have noticed that the Operating Arm (Pink) was not going under the cam (light blue) as it should. I was kind of sitting to high.
After many trial with the watch in different angle, I could not get it to work. So I wrote to my dealer and he proposed to fully wind the watch (40 turns ) and to try to press harder. Knowing that the 7750 does not like to be manually winded, I went very smoothly. But still the same. The operating arm hits the cam to high and blocks.
Since I am hard headed, I was convinced that my theory was right! I started to shop for a tool to open my 50 mm screw cover and I discovered the "Rubber Ball Trick". My Son had just what I needed
Took 30 seconds to open the case and 10 second to notice that the screw retaining the operating arm was loose, causing it to be sitting to high and contacting the wrong part of the cam. 5 Minutes later I have a functional chrono very smooth to start and stop!!
Now can I call myself a Watch smith?
