ZAPI 4Q is a compact permanent‑magnet motor controller designed for pallet trucks, floor washers and similar industrial vehicles. Common failure points include the input power supply (12 V battery pack), the MOSFET chopper stage, and the I/O connectors that carry forward/reverse signals; overheating or shorted MOSFETs often cause loss of speed control. For initial troubleshooting check: 1) Verify 12‑V battery voltage and continuity to the controller’s power terminals; 2) Inspect the MOSFET array for burn marks or excessive heat and test with a multimeter for proper conduction; 3) Confirm that forward/reverse and throttle inputs are delivering correct signals and that any error codes displayed on the console match known fault patterns.[oss-gpt-20b]