Medonica M-series: sample detector misses blood only during measurement
What happened
During normal measurements the sample detector did not register blood at aspiration. In service mode the reaction to blood was present — the reading changed (by 1 or 2, as reported in the case), so the detector itself looked functional.
What was checked
- Checked the detector response in service mode: the reading changed when blood was applied (small change, reported in the case), so the detector and its electronics were working.
- Compared service-mode behaviour with normal measurement: blood seen in service mode but missed during aspiration pointed to a break in the sample column rather than a sensor fault.
- Rinsed the fluid path with cleaning solution without disassembly; when that gave no improvement, suspected buildup on the rotary valve discs.
Cause
The engineers found contamination (crusty buildup) on the surfaces of the rotary valve discs. During normal aspiration this buildup broke the blood column, so the sample detector saw no blood during measurement, while direct application in service mode still produced a reading.
What was done
Disassembled the rotary valve and cleaned the disc surfaces. Rinsing with cleaning solution without disassembly had no effect in this case; after disassembly and cleaning the detector registered blood during measurements again. The fault was resolved in this case.
Safety
Treat the fluid path as biohazardous: power down and isolate the analyzer before opening the valve, wear gloves and eye protection when handling blood-contaminated parts and cleaning solutions, and disinfect any spills.
Lesson: If a detector responds in service mode but not during measurement, look for the fault after the sensor — in this case, valve contamination breaking the sample column — before replacing the detector.
Covered in the course: Lab Analyser 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.