|char lines line up with the bigger resistors|
there is a touch of charring under the resistors, but they all check out. Ran continuity between solder points to check traces, diode tests, all seems ok.
With it installed, the switch edge tests are fine. The optos work as they should, but opto #2 will also register when a coil is fired.
WHAT COULD BE GOING ON WHERE A VARIATION IN THE VOLTAGE ACROSS THE BOARD WOULD GIVE A FALSE-POSITIVE ON ONE OPTO, BUT NOT THE OTHERS?