presuming all levels are ok any ideas on why the tranny keeps blowing?

Something is drawing a large amount of current and you have ruled out the PCB.

You need to check the current drawn from all the devices and reference back to the current readings taken at installation.

Have you overloaded the PSU?

Have you tested the battery, could be faulty?

When I spoke to tech support they advised the panel should be able to handle the load of all attached devices, when I replaced the pcb I also replaced the battery,

If something was drawing a lot of current would it not blow out a fuse on the pcb before taking out the tranny?

If something was drawing a lot of current would it not blow out a fuse on the pcb before taking out the tranny?

Some glass blow fuses can take double there load before blowing.

You can also tell a lot from how a fuse blows.

Odd fault but should be findable with a multimeter.

Thanks for the replies, last thing any ideas why when I replace the tranny it takes upto 24 hours befor it goes again?

13.8 v on aux under load suggests no major load

Everyone has answered the Q. I'm amazed any eng never checked the obvious. I will assume that as the system was OK for a while that a resistance has moved, damaged cable, ingress, faulty device. Your meter is you friend. And of course you might want to go on a course for intruder.

As above, 13.8V would not indicate an excessive load, but check wiring for an intermittent short.

This can sometimes be picked up by the system log. See if any faults were recorded immediately before the problem.

Is there any access on the panel and only one battery fitted.

But use of a meter and logs is the only way forward, not calling tech,

tranny issue means you have a major problem. Forget what tech says regarding acceptable load for devices. Measure it and measure again. You seem to have a huge overload that is spread over your fuses. Castle (in the old days) had a psu side that could be really abused. Hardware wise it was spot on. You could take 3A from a 1.5A psu for ahort bursts no issue ( i tested) but i never blew a tx in these overload tests. You have changed the board now bud i do feel you have a HUGE overload issue

Thanks to everyone for the help, I will do some more investigating when I get back o site on Monday, if I get to the bottom of this I will post it for future reference, regards mark