What was found
EUG FLIGHT NR 2330: WHEN CONDUCTION T/O WARNING TEST PRIOR TO T/O, WARNING HORN SOUNDS WITH ELEVATOR TRIM INDICATOR IN NU HALF OF THE RANGE. WARNING HORN DOES NOT SOUND WITH INDICATOR IN ND AREA OUTSIDE OF T/O RANGE. ELEVATOR TRIM TEST OPERATES NORMAL. AIRCRAFT RETURNED TO BLOCK. MAINTENANCE REMOVED AND REPLACED PCECU 8 IAW Q400 AMM TASKS 27-00-01-000-802 AND 27-00-01-400-802. OPS CHECK AND FUNCTIONAL TEST GOOD. ALSO, PERFORMED FUNCTIONAL TEST OF THE TAKEOFF WARNING SYSTEM IAW TASK 31-52-00-720-801. FUNCTIONAL TEST PASSED. AIRCRAFT RETURNED TO SERVICE.