The JANDY E0260500B is the RS‑16 CPU/Power Control Board that supplies power and logic to a pool/spa automation system. Common failure modes on this board include burnt or cracked voltage regulator components, failed MOSFETs on the 12 V rail, and shorted I/O lines from water ingress; these often manifest as intermittent loss of control signals or a complete loss of power to downstream modules. First‑check diagnostics should verify that the main 24 V input is present and stable, inspect the board for visible damage or corrosion at the regulator pins, and test each I/O pin against the expected logic levels while reviewing any error codes displayed on the system’s LCD or via the RS‑16 diagnostic port.[oss-gpt-20b]