Tbh, I have no Idea.. my multimeter isn't accurate enough to measure the pulses in time, so my best chance of finding out when exactly the pulses fire is by hooking it up to my arduino constantly checking its input.
It basically works like this:
There's letters (A-V, omitting some like O or I) and numbers (0-8), making a total of 160 possible selections. When a combination of Letter+Number has been pressed, a motor moves a contact arm first over numbers 1-8. The contacts are wired in series, so if I'd press 5, pulses would be fired when the contact arm went over 1,2,3,4 and 5. Same thing then happens again for the letters, with a longer pause in between to detect the transition from number to letter.
Documentation on these machines (especially on the parts you usually wouldn't have to worry about when hooking it up to a regular jukebox) is quite hard to find, so unfortunately I haven't yet found anything about the pulse timing..
Greets,
Philipp