The Jandy Aqualink RS Serial Adapter (model 7620) is an EIA‑232 interface that translates ASCII commands between a home‑automation controller and the AquaLink RS pool/spa system, enabling status monitoring and limited control functions. Common failure modes include loss of serial communication due to damaged RJ45 connectors or degraded cable insulation, firmware corruption causing unresponsive command processing, and power supply voltage drops leading to intermittent operation. First‑check diagnostics should verify the adapter’s 12 V DC input with a multimeter, inspect the serial port for bent pins or corrosion, and confirm that the host controller is sending proper AT‑style commands by capturing traffic on a logic analyzer or USB‑to‑serial monitor.[oss-gpt-20b]