Servo-i/s: Self-test fails while the compressor is running
What happened
With the compressor running, the ventilator failed its self-test: the monitor microphone could not hear the monitor speaker, and the test aborted with an error.
What was checked
- Repeat the test in a different sequence: power the unit, start the self-test, and start the compressor only after the prompt to connect the test hose.
- Assess the compressor noise level by ear and compare it with a unit known to run quietly.
- Check the compressor service history — when the overhaul kit was last replaced and how many hours the unit has run since.
Cause
The engineers attributed the failure to excessive compressor noise: a worn overhaul kit after long service made the compressor loud enough to drown out the monitor speaker, so the microphone no longer picked it up and the acoustic check failed. The cause was treated as probable, based on the noise level and the service history.
What was done
Taking the monitor off the ventilator stand let the self-test complete without an error — this confirmed the noise as the cause and was used as a diagnostic step, not a repair. The fix recommended in the case is replacing the compressor overhaul kit per the manufacturer's schedule (a 10,000-hour interval, as reported in the case), with no changes to the test itself.
Safety
Before any work on the compressor, isolate the ventilator from mains power and let all moving parts stop, and before return to use run the full self-test and verify ventilation and alarms on a test lung.
Lesson: A self-test that fails only while ancillary equipment is running points to the environment rather than the tested unit, so check noise, vibration and power-up sequence before suspecting electronics.
Covered in the course: Ventilator 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.