KAP 150 Autopilot - Slow to Initialize.

[29-0363]

In a 1998 M20R I previously owned the KAP-150 has developed a fault where it can take an eternity to initialize after the Avionic Master is switched on.  Normally the AP takes only a short time for the self test, but sometimes it can take 5-6 minutes before it initializes with multiple beeps, and enables the AP to be engaged. 

 

Any suggestions where to start looking?