Siemens Emotion 16: gantry drops out and reinitialises when a spiral scan starts
What happened
The topogram scans normally, but as soon as high voltage is switched on for a spiral scan the gantry shuts down, reinitialises, and the cycle repeats. In this case the gantry had first failed to be detected at all; the new symptom appeared after the slip-ring brushes were replaced with a used set.
What was checked
- The slip-ring brushes were swapped for a used set — gantry detection came back, but the shutdown under load remained.
- A data-link test to the rotating side (DMS test data link, from the manufacturer's service documentation) was run with the gantry stationary and again during rotation at different angles.
- The transmit antenna was inspected.
- The receiver gap and its mounting/position relative to the antenna were checked.
Cause
Reported as probable: during rotation the receiver moves away from the antenna, the data link to the rotating side drops, and the gantry loses communication and reinitialises. The suspected fault is in the receiver harness or an out-of-spec receiver gap. The initial no-detection was tied to the brushes; the used set restored the link but did not remove the drop-out under rotation.
The cause is probable and was not fully confirmed.
What was done
No confirmed fix in this case. The next step was to restore the correct receiver gap and secure its mounting and harness, using the procedure from the manufacturer's service documentation done by authorised personnel; the outcome is reported as probable, not confirmed.
Safety
Before working near the slip ring, brushes, or receiver, power down and isolate the gantry drive, confirm rotation has fully stopped and stored energy has discharged, keep the high-voltage generator off, and complete the electrical safety checks before the scanner is returned to use.
Lesson: A data link that passes a stationary test can still fail under rotation — test rotating-part communication with the gantry actually spinning, and treat a used replacement part as a new variable, not a cure.
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.