The Chadwick‑Helmuth Model 11/11A/11B is a precision Vibrex system calibrator that supplies 28 VDC (or 110 VAC on the 11PS variant) to perform end‑to‑end functional checks of balancers, analyzers and associated pickups. Common failure points in this class include degraded power‑rail conditioning, faulty internal signal generators, or worn relay contacts that can cause incorrect calibration outputs or intermittent operation. First‑check steps: verify the input voltage and regulator output with a multimeter; inspect the 28 VDC supply board for burn marks or loose connections; review any error codes displayed on the calibrator’s panel and compare them to known fault lists for the Model 11 series.[oss-gpt-20b]