Trade, really? I can see why he was arsey but I didn't realise. It was a genuine question I asked him but his reaction was off the scale.. I can't deal with that kind of person..
Oh, that doesn't sound great. We had a new service manager when I was at Kings, he came from BT and to be fair made loads of changes, really made his mark and I felt he changed a lot of the way Kings operated (from a service perspective) for the better. Obviously he got the bullet.
Optical isolator - as it says on the tin.. Can you reconfigure the 232 port on C4 to do something else (doesn't matter what) to prove it works properly? Might be putting out ***** and killing the panel?
Any recent C4 firmware updates been applied? Try updating panel firmware? Do you have a ground between C4 and panel on 232? Does it still do it when you physically disconnect C4 and set from keypad?