The Allen‑Bradley 1769‑SDN Compact I/O DeviceNet Scanner is a 4‑slot module that bridges a CompactLogix or MicroLogix controller to up to 63 DeviceNet nodes, providing digital I/O and network communication. Common failure points include power supply degradation (±10 % overvoltage), loose terminal connections on the DeviceNet bus, and firmware corruption due to improper programming or sudden power loss. First‑check steps: verify that the module receives its rated 24 VDC input within ±5 %, inspect all DeviceNet termination resistors and cable integrity for shorts or opens, and review the controller’s error logs for “DeviceNet communication failure” or “Scanner module fault” codes before proceeding to reflash firmware if needed.[oss-gpt-20b]