The Simplex 4009 IDNet NAC Extender is a self‑contained adjunct panel for Simplex fire alarm control panels, housing four IDNet notification appliances (NACs), a built‑in power supply/charger, an IDNet slave interface, and two conventional hardwired NAC inputs. Common failure modes include loss of power to the extender (faulty AC input or internal PSU), communication errors on the IDNet slave link (open/shorted cable or corrupted firmware), and individual NAC faults such as blown relays or mis‑wired hard‑wire connections. First‑check diagnostics: verify 120 V/240 V supply voltage at the unit’s inlet, inspect the power supply output for correct DC levels and charger status LEDs; examine the IDNet interface for proper cable continuity and error codes on the host panel; visually inspect each NAC terminal for corrosion or loose wiring before testing with a multimeter.[oss-gpt-20b]