As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
WHILE SWITCHING AC VOLT SELECTOR SWITCH FROM EXTERNAL TO APU, SMOKE CAME FROM BEHIND BACK OF PNL AND VOLT AND FREQ GAGES BECAME INOP IN ALL POSITIONS, NO RESIDUAL EITHER. REMOVED AND REPLACED AC METER MODULE ASSY IAW 24-20-00. OPS CHECKS NORMAL IAW SAME DURING ALL PHASES OF OPERATION. NO FLIGHT NR. FLT 125 CANCELLED. AIRCRAFT WAS GROUNDED. (K)