The Monarch EUT220B is a compact industrial controller used to drive small DC or servo motors, typically mounted on motor control panels. Common failure modes for this class of units include power supply voltage dropout, overheating of the integrated driver ICs, and degradation of input/output contacts due to repeated switching; firmware corruption can also trigger “invalid parameter” errors. First‑check steps: verify 24 V DC (or specified) supply continuity and correct polarity at the controller terminals; inspect for burn marks or swollen capacitors on the board; then review any diagnostic LEDs or error codes displayed, followed by a quick continuity test of all I/O lines against the wiring diagram.[oss-gpt-20b]