Ambient conditions not within spec.

Check environmental conditions.

Blocked dust filter.

Check dust filters. Clean/replace if needed. See service procedure "Check the dust filters".

Malfunction fans of SMPS compartment.

Check for errors/warnings related to the fans of the SMPS compartment and resolve these first (connections, speed, voltage, ...).

Malfunction SMPS

Replace the SMPS. See service procedure "Replacement of the SMPS board".