Hi guys! I explain immediately the problem.
The pinball goes in attract mode, accepts credits but won't start the game. I'm able to enter in the diagnostics, the credit button works well... but not to start a game!
The CPU has new sockets, new set of roms (all verified), new 6114, new PIA in IC36 and new interboard connector.
The driver board is also functioning and tested in my other pinballs.
At the first time my thought was a short in the button or something else similar, but then I tried a sys6 CPU (I don't have other sys7 CPUs) and pushing the credit button, the game starts finally! So I think the "problem" is on the CPU...
From where can I start to solve this mystery?
Any help will be very appreciated!!!
Thanks guys!
I'm at your disposal for any further questions...

At the moment all the solenoids connectors (from 2J9 to 2J13) on the driver board are disconnected, because as soon as I connect one of them, I can hear the usual sound of all solenoids activated (remember that the driver is complete functioning)

Ok! Thanks for your reply. Firepower 2 has only 2 balls. I've just checked to start the game with balls inside but without results!
At the moment only two switches are not functioning under diagnostics: playfield tilt (sw. 49) and ball shooter trough (sw. 19). The first one is missing of diode, the second one is ok with the multimeter if closed by hands, but is not registered in the diagnostics.

Inside the headbox, there is this sticker:
"connect ground braid from cabinet and white-red wire from playfield under the wingnut with pre-connected white-red wire from insert board"..... I have only the first wh-rd wire and the gnd braid. What is the "interconnect board"?

No problem!
The 2 trough switches (09 & 10) work well and detect both balls, the pinball accepts the credit but the credit button doesn't start the match once pressed.
This pinball sucks! My friend tooks it at a very low price... and now I understand why it has a damp smell...

The solenoids are activated once the pinball is powered on... but the driver is complete working! Could it be a sympthom of a cpu issue?

The 2 trough switches detect both balls during the diagnostics, so I think they work properly. The only one is not working is the channel switch but this switch drives the initial sound.

Bump

Thanks a lot Wizard! Yes I still have the same problem. During the weekend I will take a better look under the playfield to find if there is something wrong! Finger crossed...

Update... I've tried another sys7 refurbished cpu and the FP2 works fine. So it means I have an issue on that board.
I have to re-check again it on the bench!

Another update.
I re-installed the original CPU board. It seem to works good BUT only at the power on it has a strange behaviour: some coils are activated and the first ball is fired in the launch gate. It means the first ball has to be shooted in the playfield during the attract mode. Then I can play normally...
I don't understand why these coils are energized...