As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING GND. RUN WITH ENG.'S RUNNING AND AVIONICS POWER UP, CREW STARTED THE APU. THE NR 1 INVERTER FLUCTUATED VIOLENTLY AND WAS SELECTED 'OFF'. WHEN ATTEMPT WAS MADE TO REINSTATE NR 1 INVERTER, BOTH ALTIMETERS WENT TO 60,000 FEET AND STAYED THERE. WHEN THE A/C WAS SHUT DOWN, SMOKE WAS COMING OUT OF THE REAR EQUIPMENT BAY. SOURCE WAS FOUND TO BE THE NR 1 INVERTER. INVERTER AND BOTH ALTIMETERS WERE CHANGED.