I installed a new Raymarine Ev-400 about two years ago coupled to a Mamba drive, worked quite well although a few times I got a "drive stopped" message. Restarting the A/P made everything happy. I had not used the autopilot for a while and when I engaged it the drive stiffens up but does not do its initial search for position nor does it respond to correction and then indicates drive stopped. Releasing to standby relaxes the drive. I haven't even started troubleshooting but my initial guess is that the drive has an issue. Is there a procedure to troubleshoot the unit? Can the drive be overhauled?