When there is no power on the loop the loop isolaters don't operate, i dont know gent that well have the devices you are using go isolated bases ? is one wired wrong ?
If you have it on a bench and the loop is made up of a couple of meters of cable, the loop may be to short and resistance of the loop is not enough for the panel.
No mention of one of the first muliplexed panels, the 2000 and the CATS coded alarm transmitters, Acorn at the time a great little panel, why did they have that dull green and brown colour scheme for their early panels like the 72