PLT OF SMA ACFT LOST CTL OF ACFT WHEN REPROGRAMMING FOR THE DSCNT RESULTING IN GOING ABOVE ASSIGNED ALT AND WANDERING OFF INTENDED TRACK.

Narrative

ATC CLRED US TO DSND OUT OF FL200. I TURNED OFF ALT HOLD ON AUTOPLT PRESS THE DOWN ROCKER SWITCH ON THE AUTOPLT. ACFT PITCHED UP INTO STEEP CLB. I SHOVED THE WHEEL FORWARD IN AN ATTEMPT TO LOWER NOSE BUT WAS NOT ABLE TO DO SO. I SWITCHED OFF AUTOPLT; SWITCHED OFF ELECTRIC TRIM AND USED MANUAL TRIM WHEEL TO HELP LOWER THE NOSE; HOWEVER ALT WENT CONSIDERABLY OVER ASSIGNED ALT. IN ADDITION I GOT OFF COURSE DURING TIME CTL WAS TRYING TO BE RESTORED. IN CONTINUING DSCNT BY HAND FLYING WITH FLT DIRECTOR; NOTICE FLT DIRECTOR STARTED GIVING WRONG INDICATIONS. TRIED TO CORRECT PROBLEM BY RESETTING ALL CTLS OF FLT CTL SYS AND TRIED RESETTING AUTOPLT AGAIN -- THIS RESULTED IN CIRCUIT BREAKER POPPING. ALL IN ALL; MY FLYING WAS SLOPPY DURING ALL OF THIS WITH NUMEROUS COURSE AND ALTDEVS. AUTOPLT HAS SINCE BEEN FOUND TO HAVE DEFECTIVE; PARTS IS IN PROCESS OF REPAIR. IN THE EVENT OF A FUTURE FAILURE; I WILL SIMPLY TURN OFF THE AUTOPLT AND FLT DIRECTOR ASAP AND TRY TO CORRECT ANY PROBLEMS ON THE GND. IT'S TOO DIFFICULT TO TRY TO DIAGNOSE THESE KINDS OF PROBLEMS WHILE SINGLE PLT IFR.