Siemens UMAS: blue screen during checkup
What happened
Mid-way through a system checkup the screen went to a blue screen of death; after a reboot the checkup would not pass, and the error messages gave no useful direction.
What was checked
- Measured the 5 V rail from the lambda power supply block: 5.1 V at its output but only 4.8–4.9 V reaching the UMAS input, as reported in the case.
- Inspected and re-seated every connector and contact along the path from the lambda block to the UMAS.
- Checked the 5 V LED on the UMAS board.
Cause
The 5 V supply sagged because of losses across oxidised and loose contacts between the lambda block and the UMAS; the voltage arriving at the board was too low for reliable operation.
What was done
The engineers re-seated and cleaned the contacts with contact cleaner and reconnected the path; the 5 V LED then lit as expected. The error left behind after the blue screen at the Defective Channel stage was cleared with the channel-tuning procedure (Tune Defective Channel) — a procedure from the manufacturer's service documentation, done by authorised personnel. After this the checkup passed and the fault was resolved. Case note: the UMAS2/UMAS Plus has no fan by design, and its board is reportedly often damaged when someone retrofits one.
Safety
De-energise the system and let the supplies discharge before opening or re-terminating power harnesses, and repeat the manufacturer's electrical safety tests (protective earth continuity and leakage currents) before returning the system to clinical use.
Lesson: When error messages are uninformative, measure supply voltages at the point of use — a rail can look fine at the source and still arrive low after oxidised or loose contacts.
Covered in the course: Fault-Finding Method for Medical Equipment →
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.