The Granville‑Phillips 270 is a Series 270 ionization gauge controller that manages dual thermocouple and ion gauge set points across eight decades of vacuum pressure. Common failures include degraded power‑supply modules (causing intermittent operation), electrometer drift or shorted input stages, and emission‑controller faults that lead to loss of gauge signal; improper grounding can also trigger high‑voltage arcing. First‑check diagnostics should verify the 24 V/120 W supply output, inspect the electrometer input pins for continuity and leakage, and confirm all exposed conductors are properly bonded to chassis ground before reviewing any error codes in the controller’s diagnostic display.[oss-gpt-20b]