The pilot taxied for takeoff and attempted to rotate at 70 knots. He said full aft pressure on the yoke would not cause the plane to lift off. He attempted to abort after the plane reached 90 knots, but lost control. The plane departed the runway to the right and struck a culvert in a ditch. The nose gear collapsed, and the plane nosed down. The firewall, gear, propeller and part of the fuselage were bent. The pilot said this was the first flight following repairs performed on the autopilot. The pilot said he always rolled the elevator trim wheel a half-turn forward for takeoff, since he always left the trim full aft at landing. He did not note the indicator position, since the indicator was broken prior to the accident. A postaccident inspection revealed that the mechanic repaired the indicator and set trim to neutral in order to complete the maintenance. No fault was found with the trim or autopilot system. A Cessna engineer estimated the reported trim setting would require considerable strength to overcome for takeoff.