A REPEAT SERVO MOTOR PROB ON A CITATION RESULTS IN THE TEMPORARY LOSS OF ACFT CTL; A HEADING TRACK AND ALTDEV WHILE ON APCH FREQ WITH S56; UT.

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ELECTRICAL PROB; UNABLE TO DUPLICATE; CAUSING ERRONEOUS DATA TO EFIS. ON LEVELOFF WAS ASKED TO MAINTAIN 170 KTS. UPON REACHING 10000 FT; ACFT FLT DIRECTOR SHOWED A PITCH-UP OF 20 DEGS NOSE UP. IMMEDIATELY DISCONNECTED AUTOPLT AND LARGE MANUAL INPUTS TO CORRECT ATTITUDE. ACFT GAINED 1000 FT WHEN ATTEMPTING TO RECOVER CTL. AT THE SAME TIME THE ACFT FLEW THROUGH THE LOC NEEDLE AND WOULD NOT NAV THE LOC. AFTER DISENGAGING AND THEN REENGAGING THE AUTOPLT THE ACFT FLEW NORMALLY. FOLLOWING THIS FLT I MADE 2 FLTS TO DUPLICATE THIS SCENARIO AND COULD NOT DUPLICATE THE TRIM RUNAWAY SIT. 1) DURING THE APCH MODE; I HAD ANOTHER PLT IN THE COCKPIT. ALTHOUGH SINGLE PLT OP; THE OTHER PLT HAD UNDERTAKEN TRAINING 2 WKS EARLIER. HIS PRESENCE IN THE COCKPIT WAS MORE OF A HINDRANCE THAN ASSISTANCE; AS I HAD A PLT THAT I ASSUMED WOULD ASSIST ON RADIO AND WAS SLOW TO REACT TO RESPONSES FROM ATC. 2) FAILURE TO FULLY ADVISE ATC OF POTENTIAL EMER SIT. I ADVISED ATC OF PITCH CTL PROB; BUT FAILED TO DECLARE EMER. ATC CONTINUED TO RATTLE OFF INSTRUCTIONS DUE TO VOLUME OF TFC. THE ACFT HAD PREVIOUSLY HAD AN AUTOPLT PITCH SERVO PROB; THAT THE MANUFACTURER COULD NOT DUPLICATE. I WILL CONTINUE TO TRY TO DUPLICATE THIS PROB.