Hi.... I have got it working . I agree it was unlikely to be faulty and it was defying logic..... that logic being mine, twisted and probably wrong, in what I was observing and deducing from it..... working on the premise it was the INT dialler circuit not triggering the going-high or going-low voltage transition, I was going to make use of the PA or FIRE inputs on the dialler (i.e. INT output from alarm to FIRE input of dialler).... and set about first testing this ..... measuring the alarm outputs I could see that they were normally HIGH and went LOW when active/triggered... what I noticed was that when I put the alarm in test mode and activated "FIRE" (falling voltage) it did NOT dial, but,, a minute later when de-activating that output (voltage going high, rising) it dialled.... aha.... so I must have interpreted the settings [4] incorrect. I set all these to be "ON" (illuminated) and now all 3 test alarm outputs give a correct dialler response ( and it dials me! ), yay. (I had tried all this last night I thought but maybe just got in a muddle with all the tests I did!)
So..... it could have been me being thick, or, just tired and frustrated with it last night !!! it now tests out fine, and, I have a cunning plan if indeed that INT circuit on the dialler is intermittently not behaving itself..... [can't think of a reason this wouldnt work, it's just 3 similar alarm outputs and 3 similar dialler inputs, labelled for sanity when setting up specific voice messages for each one....
Thanks all...... if nothing else this thread gave me some re-assurance and hope and encouragement to not give up (which to be honest was also due to the hefty price tag of a replacement)