A DORNIER 328 JET ON TKOF CLBED AT 700 FT; DECLARED AN EMER; AND DIVERTED DUE SMOKE IN THE COCKPIT CAUSED BY THE APU GENERATOR OVERHEATING.

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ON FEB/WED/02 AT APPROX XA40; I WAS THE CAPT OF FLT ABCD; A PAX CARRYING FAIRCHILD 328 REGIONAL JET FOR ACR X. MY CREW AND I WERE ASSIGNED FLT ABCD AS A SCHEDULED FLT FROM ZZZ TO BTV IN ACFT X. THE ACFT HAD A DEFERRAL FOR THE CABIN HX FAN AND ANOTHER DEFERRAL FOR THE FORWARD RECIRCULATING FAN. WE COMPLIED WITH THE MEL OPERATING PROCS FOR THE DEFERRALS. WX CONDITIONS WRE IMC DUE TO PRECIPITATING SNOW; LOW VISIBILITY; AND A LOW CLOUD CEILING. ON DEP; SHORTLY AFTER ROTATION; WE RECEIVED A MASTER CAUTION AND AN ASSOCIATED AMBER CAS FOR 'APU GENERATOR OVERHEAT.' WITHIN A FEW MOMENTS OF THE APU GENERATOR OVERHEATING; SMOKE ENTERED THE COCKPIT. WE EXECUTED THE SMOKE MEMORY ITEMS. WE THEN COMPLIED WITH THE SMOKE QRC AND QRH. WE FURTHERMORE COMPLIED WITH THE QRH FOR 'APU GENERATOR OVERHEAT.' WE NOTIFIED ATC AND OUR FLT ATTENDANT. OUR FLT ATTENDANT ADVISED THAT THERE WAS NO SMOKE IN THE CABIN AND THAT ALL CABIN INDICATIONS WERE NEGATIVE FOR SMOKE OR FIRE. ALTHOUGH THE SMOKE IN THE COCKPIT HAD SUBSEQUENTLY CLRED; I INITIATED A PRECAUTIONARY RETURN TO ZZZ. WE NOTIFIED OUR FLT ATTENDANT OF THE EMER ITEMS WITH NO EVAC REQUIRED. WE ALSO NOTIFIED COMPANY. DURING OUR RETURN FOR APCH INTO ZZZ; WE ADDITIONALLY RECEIVED AN AMBER FAULT WARNING COMPUTER ON BOTH PRIMARY FLT DISPLAYS. WE ALSO LATER RECEIVED A MASTER CAUTION AND AN ASSOCIATED AMBER CAS FOR 'CABIN PRESSURIZATION CTL SYS MISCOMPARE.' ACCORDINGLY; WE COMPLIED WITH THE QRH FOR THESE ANOMALOUS INDICATIONS AND CAUTIONS. WE LANDED SAFELY IN ZZZ. DURING THE TAXI INTO THE GATE; OUR FLT ATTENDANT CALLED AND ADVISED THAT THERE WAS A LIGHT FOG-LIKE VAPOR; WITH NO ODOR; COMING FROM THE VENTS IN THE CABIN. SHE FURTHER INQUIRED IF IT MIGHT BE SOME SMOKE. WE ADVISED HER THAT IT WAS MERELY CONDENSATION FROM THE ECS PACKS; THAT ALL INDICATIONS WERE NORMAL; AND THAT WE HAD THE SAME VAPOR COMING FROM THE COCKPIT VENTS. THE FIRE DEPT AND MAINT LATER RECONFIRMED THAT THE LIGHT VAPOR WAS MERELY CONDENSATION FROM THE ECS PACKS.