Mircomark 6 zone alarm won't hold its settings?

We have a micromark wired 6 zone easyfit intruder alarm which sets correctly and holds the setting for a short while but if left unattended for any length of time when we return the alarm seems to have tripped out and we are met with an intermediate beeping sound not the usual fast one. The access code sometimes has to be pressed twice to clear. We have had a new control panel and have changed the battery. The only thing we can see that may be remotely wrong is that there is a slight scorching mark on the transformer and wonder if this has perhaps burnt out. Any ideas?