Abbott A25: baseline error after rotor replacement
What happened
Baseline error, appearing mostly after a rotor change. The optical system tests passed and no bubbles were found in the cuvettes, so the obvious optical causes were ruled out.
What was checked
- Run the optical system tests — reported normal in this case.
- Inspect the cuvettes for bubbles — none found.
- If the optics test clean, suspect the lamp supply; fitting a known-good power supply from a decommissioned unit shows whether the fault follows the supply.
Cause
In this case the suspected cause was a Schottky diode on the lamp power supply putting noise onto the lamp circuit, which showed up as a baseline disturbance, especially after a rotor change. The engineers treated this as a probable cause, not a confirmed one.
The cause is probable and was not fully confirmed.
What was done
Replace the Schottky diode on the lamp power supply, or fit a known-good power supply — in this case, taken from a decommissioned analyzer. The outcome was reported as probable, so confirm with optical and baseline checks after the swap.
Safety
Isolate the analyzer from the mains and allow the power supply capacitors to discharge before opening the PSU, and complete performance verification before returning the analyzer to use.
Lesson: When a baseline error survives clean optical tests and bubble-free cuvettes, check the quality of the lamp supply — electrical noise can mimic an optical problem.
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.