Hate to be a wet blanket but without an actual schematic and some reasonable test equipment you are asking for more problems than you are starting with. Replacing a bad opto isolator or other micro miniature electronic component is not plugging in a new tube like the by gone days. Should be done in proper static control environment with appropriate anti static tools. 1 Meg ohm to real earth ground +/-10% for the work surface and 40 - 60 % relative humidity.
i'm not an idiot, i have my own shop where i do stuff like this regularly. I understand that i need a schematic, that's why i'm patiently waiting that someone can [virtually] dust off one their folders in their computer and email me that service manual or schematic.
Beseler, those greedy bastards, charge $75 for the service manual. Absolute insanity, for an item they longer support..