What was found
UNCOMMANDED REVERSION TO CWS WITH AUTOPILOT ON AND ACFT LEVEL AT FL340. NO AUDIBLE OR VISUAL WARNING OTHER THAN FMA INDICATING, ALT HOLD AND CWS R. B AUTOPILOT STILL ENGAGED IN "CMD". RE-ENGAGED LNAV AND YNAV WITHOUT INCIDENT. ACFT GROUNDED. PERFORMED DFCS FAULT REVIEW BY FLIGHT DECK EFFECT, 4 OCCURRENCES OF MODE REVERSION WERE LOGGED, FAULT MSG 22-11822 FOR ALL OCCURRENCES. T/S IAW FIM 22-11, TASK 811. DFCS BITE PASSED. REMOVED SN 41GXP4 AND INSTALLED SN 17HG28. OPS CHECKS GOOD.