WHILE EN ROUTE, THE PLT ENCTRD HEADWINDS & TRACE RIME ICING. HE MADE A CLIMB FROM 17,000 FT TO FLT 190, THEN TO FL 210. AFTER CRUISING AT FL 210 FOR ABOUT 27 MIN, THE ACFT ENTERED A DSCNT (W/O ATC CLNC). RADIO & RADAR CONTACT WERE LOST IN THE VCNTY OF WERE THE ACFT CRASHED. JUST BEFORE IMPACT, THE ACFT WAS OBSERVED TO DSCND OUT OF LOW CLOUDS IN A SPIN. THE PLT HAD BEEN ISSUED A CANADIAN INSTRUMENT RATING ON 1/11/88, BUT IT WAS VALID FOR ONLY 12 MOS. A PERSON, WHO HAD GIVEN THE PLT PROFICIENCY FLT TRAINING IN PREPARATION FOR AN INSTRUMENT QUALIFICATION CHECK, REPORTED THAT HE HAD RESERVATIONS ABOUT THE PLT'S ABILITY TO FLY IN INSTRUMENT CONDITIONS WITHOUT AN AUTOPLT. AVIONICS PERSONNEL AT THE DEPARTURE ARPT RPRTD THE PLT HAD ENCTRD AN AUTOPLT MALFUNCTION ON THE PREVIOUS FLT & THAT THEY HAD FOUND AN ELEC SHORT IN THE AUTOPLT DISCONNECT SW ON THE COPLT CTL YOKE. HOWEVER, THEY WERE UNABLE TO REPAIR IT DUE TO LACK OF A REPLACEMENT PART. RPRTDLY, THE PLT BARROWED A SOLDERING IRON TO REPAIR IT HIMSELF.