Quoted from pinball_ric:Using a multimeter I get 12v on both sides of R56 and R58.
Typically is you have the same voltage on both sides of a current limiting resistor, it means there is no current flow usually caused by an open circuit. The most likely cause of this is a broken thru hole at one of the transition points, or a broken run. I would have to look a little at this circuit in more detail to provide more circuit specific information, like I mentioned previously, a problem in this area will effect half the board, not one just one opto; this is easy to verify on he bench.
For bench testing this, you may want to also tie your 2 column pulses (J5-9 and J5-10) to a source (12V, gnd, or a pulse), as leaving these open can cause erroneous readings; i usually use the pulse function of my logic probe for this when working on the bench.