As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
THE SLATS FAILED TO EXTEND WHILE PILOTS WERE PERFORMING THE INSPECTIONS BEFORE TAKEOFF. THE SLATS LOCKED OUT WHILE MECHANIC PLACED THE FLAP/SLAT SELECTOR TO DN POSITION. SLAT UNBALANCE LIGHT CAME ON SIMULTANEOUSLY. TROUBLESHOOTING FOUND THE FSECU OUTPUT VOLTAGE WAS OUT OF TOLERANCE.