There is a fault with the alarm. With the system in engineering mode, selecting 97/Enter (Engineer Walk Test), the display shows a tamper fault with zone 4.
I have shorted zone 4 A/T loop and also zone 4 alarm loop at the panel, and the fault persists.
My suspicion is possibly the TC4021BP shift register associated with the zones 1 to 4, but it could be a problem with the dirving circuits.
Does recognise this fault? Are circuit diagrams available?