this is a silly question but have you made sure its not the contacts at the flipper button causing the problem? (i am assuming it has contacts and not optos as the manual does not show optos)

try lifting the play field and pressing the contacts from the inside towards the flipper button (after starting the game or in test mode) if the flipper works every time when you do this then it is the contacts.

Andrew

Both bottom flippers work fine top right and top left are intermittant so flipper buttons are working .
Im confidant that the problem is either Q6 or U2 on the fliptronics board will try and find some time this weekend to sort it out.

Cheers

John