The Haas 4015J‑A is a brushless servo amplifier rated at 15 A continuous/30 A peak, used on CNC machine axis drives and equipped with an LM339 comparator and low‑voltage power supply circuitry. Common failure modes include a burned surface‑mount capacitor (C45) on the low‑voltage side, coolant contamination of motor connectors causing high‑current alarms, and degraded or frayed signal cables that trigger loss‑of‑signal conditions. Initial diagnostics should verify proper 24 V DC input to the amplifier, inspect the motor cable connector for corrosion or coolant residue, and measure resistance from pins A, B, and C to chassis ground; also check the low‑voltage supply rails for voltage sag and examine the LM339 comparator output for erratic behavior.[oss-gpt-20b]