What was found
MCP LOCKOUT ON DESCENT. CONTINUOUS ALT ALERT AND ALT WINDOW FROZEN AT 50000. COMPLETED QRH PROCEDURE PANEL RESET SUCCESSFULLY. GROUNDED - YES. PERFORMED B737-800 FIM 22-11 TASK 803, AFTER RESET OF C/B'S ALL MCP WINDOWS OPERATE NORMALLY, PERFORMED DFCS MCP AUTO TEST WITH NO FAULTS FOUND. A/C OK FOR SVC. REMOVED & REPLACED MCP REF B737-800 AMM 22-11-34. ACCOMPLISHED MCP INSTALLATION TEST REF AMM 22-11-34-740-801, LRU REPLACEMENT TEST FOR MCP (GP 32) REF AMM 22-11-34, DFCS LAND VERIFY TEST (GP 49) REF AMM 22-11-00, AND HGS SYSTEM TEST REF SMM 34-36-00, OPS CK NML.