As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AILERON TRIM ACTUATES OPPOSITE TO SWITCH POSITION. WHEN ROCKER SWITCH IS HELD TO "LWD" TRIM MOVES RIGHT WING DOWN AND VICE VERSA. REMOVED FROM SERVICE. PERFORMED OPERATIONAL CHECK OF AILERON TRIM SYSTEM IAW TASK 27-13-00-710-802 AND CONFIRMED AILERON TRIM OPERATES OPPOSITE OF COMANDED SELECTION. REMOVED AND REPLACED TRIM CONTROL PANEL IAW Q400 AMM 27-13-16-000-801 AND 27-13-16-400-801, ALL OPS CHECKS GOOD. RETURNED TO SERVICE.