Thanks for the additional info guys. I'll get the servos checked although I'd be surprised they are faulty ( but you never know!) . The head is mounted vertically on the main panel. The installation was done many years ago but has done very little work, most likely around 150 hrs probably a lot less.
Speaking to a 'cone head' tech guy he mentioned that the internal gyro of the unit maybe faulty because the Hdg display numbers tends to have a mind of its own. Am now looking at the hardware installation beyond actual plugs and connections. I'll keep you guys posted, we can all learn & this is a great forum for that