As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
A/P B VERT SPEED CONTROL WHEEL WILL NOT ACCEPT CHANGES. IT REMAINS LOCKED INTO THE RATE WHEN INITIALLY SELECTED. A/P A WORKS WELL. GROUNDED - YES. VERTICAL SPEED WHEEL CONTROL FAILS MCP TEST - DFCS BITE. REF B737-800 AMM 22-11-34, REMOVED/REPLACED MCP. OPS CHK'S GOOD REF. SAMEA MM. LLM TESTS GOOD.