The FMC 5800 Membrane Switch Panel is a rugged touch‑key interface used on FMC’s 5800 line of industrial motor controllers and balancers. Common failure modes include degraded or broken contact pads from repeated actuation, corrosion or moisture ingress at the panel connectors, and misaligned keying that can cause intermittent signal loss. For this unit, check the PCB for visible damage or burnt traces, verify that all membrane switches are firmly seated and that the back‑panel mounting screws are secure. First‑check diagnostics: confirm power to the controller (voltage rails within spec), inspect the switch contacts with a multimeter for continuity, and review any error codes logged by the FMC system that reference I/O or panel faults.[oss-gpt-20b]