Update on the Alarm saga.
I decided to buy a new battery, put my test meter across the terminals and didn't get a reading, did the same on my old battery, no reading, turns out my old faithful multimeter had given up the ghost.
Got my new meter out, tested both batteries, both reading over 13v, checked the (charging output) to the battery over 14v. so the battery and charging circuit were ok all the time.
Both fuses are fine, I removed the board checked for any damage behind it, nothing visual.
Removed the keypad assembly and checked behind that for any signs of burning or damage, none to be seen.
Fitted everything back together, leaving the front control panel off,
I put the 13amp fuse back in and the internal alarm activated, input my code and it stopped the alarm, thinking it must have righted itself, I put the front panel back on, tried setting the alarm, same again, all 4 zones in fault, I removed the front panel, immediately this set the internal alarm off, I input the code and the alarm stopped.
Tried removing the front panel with just the battery connected and also with just the mains connected and both times the internal alarm activates as soon as I remove the front panel. So the alarm does activate at least via the tampering of the panel.
Also when My battery failed 4 years ago, it burnt the circuit board as acid leaked from the battery onto the board (so I thought at that time) so I purchased a brand new board at the same time as the battery, so things aren't that old.
I don't have a problem with buying a new board, I just don't want to do it, only to find the fault lies elsewhere. If you guys are convinced it has to be the board, I'll go along with that unless you have any more suggestions in light of the further info I've provided