The Jelus 700D is a dedicated melting furnace controller used in high‑temperature processing applications, typically interfacing with heating elements and temperature sensors via analog or digital I/O. Common failure modes in this class of units include power supply voltage sag, over‑current on the heater output stage, burned‑out MOSFETs or relays, and corrupted firmware or configuration memory due to power interruptions. Begin troubleshooting by verifying that the input voltage is within spec and that the controller’s internal regulator is stable; check all heater driver outputs for correct PWM duty cycles and inspect for visible arcing or component damage. Confirm sensor connections and read any diagnostic error codes displayed on the panel, then perform a functional test of the I/O ports with a multimeter or oscilloscope before proceeding to deeper diagnostics.[oss-gpt-20b]