The Switching Systems International PFS400‑28‑1‑1 20‑0046‑009 B2 Control Board is the main logic board for a PFS‑400 series variable frequency drive, handling motor control, I/O interfacing and protection functions. Common failure points on this class of boards include degraded power‑rail regulators (especially the 24 V DC supply), burnt or cracked surface‑mount components around the microcontroller and MOSFET drivers, and firmware corruption that can lock the drive in a fault state. Initial troubleshooting should verify the input AC voltage and the regulated DC rails with a multimeter, inspect the board for visible damage or residue on key ICs, and read any diagnostic codes from the drive’s status LEDs or display before proceeding to component replacement or re‑flash of firmware.[oss-gpt-20b]