Siemens Definition Flash: gantry shuts down during start-up and never initialises
What happened
The scanner would not start: the gantry never completed initialisation and, as reported in the case, shut down after about ten minutes. The gantry stop interface blocks held steady status codes (01 on one block, changing to 12 after the host computer started; the other block stayed at 01, per the case). A firmware flash was only possible in Emergency mode and never completed. One stop-chain relay (K8 as reported) pulled in for minutes while the other two never actuated.
What was checked
- The gantry control unit (UMAS) was checked on another machine of the same type and proved serviceable, so it was ruled out.
- Emergency-stop buttons and protective limit switches were checked.
- The External_Stop chain was traced end to end using the procedure from the manufacturer's service documentation (performed by authorised personnel).
- Fuses on the gantry power distribution unit (PDR) were checked.
- The stop-chain relays were observed at power-up: one held in for minutes while the other two never pulled in, pointing to a supply problem rather than an open safety chain.
Cause
The engineers found a burned resistor in the power feed circuit: one of the supply phases never reached the gantry. With that phase missing, the gantry could not initialise, and the External_Stop indication was a consequence of the dead supply path, not of a faulty stop chain itself.
What was done
The engineers replaced the burned resistor in the power feed circuit. Power to the gantry was restored, the system started and completed initialisation, and the case was reported as solved.
Safety
Isolate the scanner from the mains and verify absence of voltage before opening the power distribution area — capacitors can hold a charge — and do not return the system to clinical use until the External_Stop chain is fully restored and proven to function.
Lesson: An External_Stop-style fault can be caused by a missing supply rather than by the safety chain itself, so confirm what actually feeds the chain before replacing its components.
Covered in the course: CT 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.