PWM 391‑4101‑440 / 8507741 is the main logic board of a Parker/Hyster hydraulic control unit used in forklifts and other heavy‑equipment hydraulics. Common failures on this board include power supply regulator burns, IC die‑breaks (especially the PWM driver), burnt or cracked traces from high‑current chopper circuits, and relay contact wear that causes intermittent signal loss. Initial checks should verify 24 VDC input stability, inspect for visible burn marks or loose solder joints, and confirm that all I/O pins to the hydraulic valves and pressure transducers are receiving correct logic levels; a quick continuity test on the chopper output traces can rule out open circuits.[oss-gpt-20b]