C208 pilot experiences autopilot failure at 10000 feet; followed shortly by electrical fumes and smoke. The autopilot servo circuit breaker was found tripped and the reporter elects to divert to the nearest suitable airport.

Narrative

In cruse at 10;000'; I experienced some difficulty with the autopilot maintaining an altitude (a problem which was reported the previous week; but was unable to duplicate to maintenance). This action was intermittent. Out of curiosity; the emergency checklists were consulted the first time this happened to see if there was any suggested action for troubleshooting. With nothing available; I dismissed any idea of troubleshooting and continued with the flight. Approximately 45 minutes in to the flight; the red TRIM light as well as the P annunciator on the autopilot illuminated and the autopilot was simultaneously disconnected. A few seconds later; the SERVO circuit breaker tripped. A couple minutes went by and I began to notice an electrical odor in the cabin. I turned on the aft cabin light and noticed smoke in the aft area of the cabin. At this point ATC was contacted regarding the situation and I asked for the nearest airport to land at immediately. VMC was encountered at about 8000'; from that point; a normal descent was initiated and a normal; uneventful landing took place. Based on the knowledge I had of the autopilot acting incorrectly during the flight; I suspected that the pitch servo was faulty and caused the autopilot to disconnect as well as tripping the SERVO circuit breaker. Because of this knowledge; I determined that there appeared to be no further threat to the aircraft once the breaker tripped; however I still wanted to land because of the smoke/smell and to get the equipment looked at to identify any further electrical damage that may have occurred. Because the incident appeared to be isolated to the autopilot (which was now turned off); I elected not to execute the the 'Electrical Fire In Flight' checklist which would effectively turn off all power to the airplane and unnecessarily complicate the incident. The following day; maintenance was dispatched and upon inspection; he found that the pitch servo was generating smoke when power was applied to the unit and that no additional damage occurred. The autopilot was deferred per the MEL and the aircraft was returned to service. While we are unable to predict electrical anomalies like this; we can strive to ensure we are prepared for abnormal incidents by doing our best to always have an 'out' or an alternate plan of action.