The Perkin‑Elmer PS 1120‑3 is a compact industrial process controller that integrates programmable logic and multiple I/O channels for controlling motors, valves, or other actuators. Common failure points in this class of units include degraded power‑supply capacitors (leading to high ripple or over‑voltage spikes), burnt MOSFETs or driver ICs from overload, and damaged input/output connectors due to mechanical stress or corrosion. First‑check diagnostics: verify the main AC supply voltage and ensure all safety interlocks are engaged; inspect the internal power‑supply board for swollen electrolytics or burn marks; and test each I/O terminal with a multimeter for continuity and correct voltage levels, noting any error codes displayed on the panel.[oss-gpt-20b]