What I don't understand is how you managed to do damage in this case; surely part of your body was up against the grounded side-rails, in which case you should have been shocked instead of the components? Unless you were either not in contact with anything grounded, or you managed to position your hand so that it was easier to get to ground through the opto board than through your body to the rails. What I'm saying is, you should make sure ground is really grounded. When I got my TZ, the grounding strap was broken, and so none of the metal on the cabinet was grounded.

That led to me wasting two evenings trying to find out how high voltage was shorting to the switch matrix (it was a TZ, and the right ramp was at +50v, so a missed shot rolling just right would hit the clock switch from behind and fry the UNL2803) - and that's actually what I was suspicious of. Clipped one lead to the grounded metal on the cabinet, other to the ramp - nope, no voltage on it, must be something else. 2 days later, I see the broken grounding strap and fix it, and promptly electocute myself by leaning on the metal rail and touching the ramp area.