Thanks for the prompt and helpful responses again all.
@sigmadelta:
I already have the EX40 Manual but thanks very much for the Siemens equipment manual, and recommendation.
I don't have any wiring diagram, but I do have a labeller and plenty of time, so if it comes to it i'll definitely use both whilst I create it ;-)
@parky:
As my major unfamiliarity is the programming, (although I have done my share of perl, bash, B.A.S.I.C, x86 assembler, C++, DOS batch files), anything that makes the conversion easier is attractive. However if hardware replacement becomes the goal then I'll ask a professional to take over, and bow out of the fix. If I could talk to the EX40 then I could pull off the program and check that it's correct, (I'm willing to learn it to try to fix this).
The misbehaving output is actually switching on when it shouldn't, so the hardware is working. I've disconnected the output wiring and the equipment doesn't come on, proving the cause back into the controller, and not an external wiring short. If the program tuns out to be correct I'm willing to try to change the output, and program to suit, to try to fix this.
If only I could get the comms working.....