The Sieb 21.45.1D/10 KVA Control Unit is a high‑power frequency converter controller used in industrial motion control systems. Common failure points for this class of units include overheating of the power MOSFET array, degradation of the gate driver circuitry, and failure of the I²C or CAN bus communication modules due to connector wear or solder joint fatigue. Begin troubleshooting by verifying that the 400 V input is within spec and that all fuses/overcurrent protection devices are intact; then inspect the PCB for burn marks, cracked traces, or swollen electrolytic capacitors. Finally, check the diagnostic LEDs and any logged error codes via the serial or Ethernet interface to isolate whether the fault originates in the power stage, control logic, or communication subsystem.[oss-gpt-20b]