hi there,
check my review for the 1510 and the 1516:
http://www.crazywatches.pl/omega-1510-m ... rdust-1974
http://www.crazywatches.pl/omega-1516-m ... meter-1976
you might have issues with the recessed button due to bad connectivity with the movement.
on the below picture in the bottom right corner you can see a thin plate on the right side of the movement just below the stem/crown.
the recessed button must touch this plate correctly thus open the caseback and clean the button from the inside and outside with some alcohol and/or brush the surfaces including the plate on the movement: