As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
YLW-GPU QUIT. AIRCRAFT LOST POWER AT GATE. DETECTED AN ELECTRICAL ODOR. SHUT OFF BATTERY. GOT NEW GPU. WHEN POWER RESTORED, SQUEAL OVER SPEAKERS. MAINTENANCE SWAPPED AUDIO PANELS BETWEEN OBSERVER AND CAPTAIN. CHECKS GOOD. RETURNED TO SERVICE. NO PARTS REPLACED. (A)