The Granville‑Phillips 307 Vacuum Gauge Controller is a rack‑mounted pressure measurement and control device that supports up to four transducers and multiple process outputs (analog, relay, digital). Common failure points in this class include power supply degradation (especially the internal 24 V DC rail), capacitor leakage or ESR rise on the input filter board, and drift or loss of calibration in the gauge‑to‑output conversion circuitry. First‑check diagnostics: verify the external AC input voltage and the controller’s internal DC output with a multimeter; inspect the power supply PCB for bulging capacitors or burnt traces; and review any error codes displayed on the panel or logged via the serial interface to identify stuck relays or out‑of‑range pressure signals.[oss-gpt-20b]