RWY EXCURSION.

Narrative

I LANDED ON RWY 36R AT TPA AND ON MY ROLLOUT; I BEGAN BRAKING AND EXCHANGED THE TILLER FOR MY NOSEWHEEL STEERING. UPON DOING SO; THE ACFT VEERED SHARPLY L (NOSEWHEEL HAD TO HAVE GONE FULL L). I TRIED TO REGAIN CTL WITH THE TILLER; BUT IT WOULD NOT RESPOND SO I DISENGAGED AND USING DIFFERENTIAL BRAKING AND RUDDER INPUTS I WAS ABLE TO GET CTL ONLY AFTER THE L MAIN HAD GONE OFF THE RWY. WE WERE DOING ABOUT 60 KTS WHEN I ENGAGED THE TILLER. AFTER STOPPING; THE STEERING SEEMED TO WORK AGAIN; SO I GOT BACK ON THE RWY AND TAXIED TO THE RAMP WITH NEITHER GND NOR TWR SAYING ANYTHING. THERE WAS NO ACFT OR RWY DAMAGE. ALSO; NO INJURIES WERE RPTED. I GNDED THE ACFT AND MAINT LATER FOUND A PROB WITH THE NOSEGEAR FEEDBACK POTENTIOMETER. I SUBMITTED THIS RPT TO DOCUMENT A POTENTIALLY HAZARDOUS PROB WITH THE EMB-120. WE HAVE ANOTHER EMB-120 THAT; AS YOU TAXI; THE NOSEWHEEL FOR A SPLIT SECOND AT A TIME WANTS TO TURN L; HOWEVER; THIS HAS NOT YET CAUSED ANY PROBS EXCEPT GRAY HAIR. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: TO USE THE NOSEWHEEL STEERING; THE CAPT MUST FIRST PUSH THE TILLER DOWN INTO A DETENT; THEN TURN THE TILLER TO THE R OR L. THE TILLER HAS NO FUNCTION WHILE IN THE 'UP' POS AND CAN BE MOVED TO EITHER SIDE WITH NO EFFECT. IN THIS INCIDENT; THE ACFT IMMEDIATELY TURNED HARD TO THE L AS SOON AS THE CAPT PUSHED THE TILLER INTO THE DETENT BUT WITH NO L TURN COMMANDED. THE RPTR'S ACR PURCHASED OR LEASED 2 BRASILIAS FROM ANOTHER ACR. BOTH OF THESE ACFT HAVE HAD NOSE STEERING PROBS. OTHER ACFT IN THE FLEET HAVE HAD NO SUCH PROBS. AN INTERESTING SIDELIGHT: THE ACFT WENT OFF THE SIDE OF THE RWY IN A CLOUD OF DUST AND THEN BACK ONTO THE RWY VERY QUICKLY. THE ATCT WAS NOT WARE OF THIS UNTIL THE FLC CALLED IT BE TELEPHONE. FORTUNATELY THE ACFT DID NOT NEED ANY HELP.