Quoted from NPO:
Put the game in switch test mode.
Take the mist ball out of the right gate. Take your hand and run it across the middle of the PF. Do you hear an audible "beep" of your hand breaking the opto beam?
You should be able to run your hand (from the coin door towards the ramp entrances) back and forth each direction and hear an audible beep of the opto beam being broken over and over again.
No opto is triggering in the middle of the playfield. The only opto that is registering is the left opto where the ball ends after Mist. The cross playfield opto, as well as the ‘hold’ opto on the right is not working in test.
Based on research, it seems it could be the opto itself, or I need to replace some components on the ‘small’ board, or replace the big opto board with the HomePin replacement... hmm.