What was found
STAB OUT OF TRIM LIGHT ILLUMINATED WHEN AUTOPILOT ENGAGED AFTER A WHILE NOT IMMEDIATELY AFTER ABOUT 30 MINUTES AT CRUISE ALTITUDE. LEFT LIGHT ILLUMINATED WITH LEFT A AUTOPILOT RIGHT LIGHT ILLUMINATED WITH RIGHT B AUTOPILOT. GROUNDED - YES. ACCOMPLISHED DFCS SPEED/STAB TRIM TEST #32. RECOVERED INTERMITTENT FAILURES FOR: TRIM CLUTCH, STAB POS SNSR AND TRIM DOWN. TRIM WHEEL ONLY TURNS "NOSE UP" WHEN PASSED. FOLLOWED B737-800 FIMS 22-14-818 & 22-15-818. 22-15-818 STEP (5)(C) & (5)(E) FAIL. REPLACED STAB TRIM C/O RELAY R384. NO FIX. STAB TRIM TEST NO LONGER PASSES ALSO RECOVERED TRIM UP FAIL 22-11180 TO GO WITH PREVIOUS FAULTS. SUSPECT STAB TRIM SERVO MOTOR BAD FROM STOCK. REPLACED STAB TRIM MOTOR REF B737-800 AMM 27-41-71. STAB TRIM MOTOR TEST GOOD, STAB TRIM MOTOR A/P TEST GOOD. ACCOMPLISHED SPEED/STAB TRIM TEST 5X TIMES ALL TESTS PASSED TRIM WHEEL NOW TURNS BOTH DIRECTIONS. ACCOMPLISHED LAND VERIFY TEST, TEST GOOD. 3 EA CBS PULLED/RESET.