As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
MCP ALTITUDE WINDOW LOCKED UP READING 50000' OUR ALTITUDE WAS FL350 AND WE HAD BEEN CLEARED TO 10000' IT HAPPENED AFTER WE SPUN THE KNOB. ALTITUDE AURAL WARNING WAS HAPPENING. FOLLOWED QRH AND THE PROBLEM WAS FIXED. GROUNDED - YES. ACCOMPLISHED FIM 31-62 TASK 801 AND FIM 22-11 TASK 803. ALL TESTS PASSED, NO CURRENT FAULTS.