Dräger Primus: self-test fails, machine runs on battery only
What happened
The anesthesia machine failed its self-test with errors and warnings and refused to run from mains power, operating only on battery.
What was checked
- Usual first steps for a failed self-test were tried: absorber volume check, cleaning the breathing-block seal, overhaul of the breathing block — none of it changed anything.
- Since the machine accepted battery but not mains, the engineers moved to the power supply itself and found a burned varistor at the high-voltage mains input.
Cause
The mains power path was dead because of a burned-out varistor at the high-voltage input of the power supply; the battery path stayed alive, which is what pointed to the power inlet rather than the breathing system.
What was done
The burned varistor at the high-voltage mains input was replaced; after that the machine passed the self-test and accepted mains power again (reported as solved in the case).
Safety
Work on the mains input only with the cord unplugged and after the power supply capacitors have discharged — the input stage can hold a lethal charge — and since a burned varistor usually means the machine took a mains surge, run the full electrical safety test before returning it to use.
Lesson: When a machine runs on battery but refuses mains, start at the power inlet, not at the breathing system.
Covered in the course: Anaesthesia Machine Service — Level 2: Fault-Finding →
Written from an anonymised case shared by service engineers. It is not a manufacturer instruction and grants no authorisation. Independent note; names are trademarks of their owners.