As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CLIMB-OUT, THE VERTICAL SPEED WHEEL MOVED TO FULL NOSE UP POSITION WITH "B" AUTOPILOT SELECTED. IN CRUISE AUTO STAB "B" LIGHT ILLUMINATED SEVERAL TIMES. AT FL 340 WITH ALTITUDE HOLD SELECTED, VERTICAL SPEED VARIED +/- 2000 FPM. WITH AUTOPILOT OFF, THE AIRCRAFT WAS UNSTABLE IN PITCH AXIS. REPLACED INBOARD ELEVATOR CONTROL UNIT AND OPERATIONALLY CHECKED GOOD.