You can check that F8 does exist in your machine.
Go into switch test T.1, pull J905 from fliptronic board and short pin 5 with pin 6.

Does that trigger F8 in the switch test ?

If so, possible something wrong with flipperbutton-optoboard in cabinet.

F8 FT2.jpg

Okay, for the record, F8 is the Upper Left Flipper *opto*.

Even if the game does not have an upper left (or right) flipper, the OPTO should still work. When you press the flipper button in, both F4 (L Flipper opto) and F8 (UL Flipper Opto) should activate. (Or for the right flipper button, F2 & F6) Again, this should happen *regardless* of whether the game HAS an upper flipper.

However - there is some exceptions!
SOME games that do not use the upper flippers will have the upper flipper switches (EOS, Opto) wired into switches on the playfield. (For example, Cirqus Voltaire has the two upper EOS switches wired to the spinners.)

It's usually something that happens when the plastic (or metal) arm of the flipper button opto gets slightly bent out of whack. The interrupters aren't clearing the one opto. Try adjusting the arm.

Tech:

The F8 switch is activated when the opto on the little board stops being interrupted. That is to say, the standard state of the opto is the beam from one side not making it to the other. This is so if the opto fails, it doesn't make the game think the flipper button is stuck pressed. When you push the button, the little plastic bit gets moved up, and out of the way of the opto beam. Now the beam can make it from one side to the other, and it registers a button press.

Coyote comment FTW ^

It’s on your left flipper board, I believe it’s the lower opto.

So weird, as I just encountered this on my CFTBL. Turned out it was an improperly seated ribbon cable on the fliptronics board.