I think you're right there cavey. I have got everything working except for some opto's. I don't have any switch column errors (I think) and no phantom switches being triggered. I have installed a new opto pcb and it has an led for each opto and all opto's trigger on the LED readout but about 4 won't trigger in the switch test. Some do if I unplug the auto fire cable but don't when its plugged.

I think the cause of my problems may have been the LED clock pcb as it causes a Slam Tilt error if I plug it in. I don't get this with the old clock pcb. But I have been using the new clock pcb for ages.

Now I'm pretty much done trying to fix it. I even replaced the opto's on the auto fire but made no difference