Philips Brilliance 10: Gantry intermittently fails to start
What happened
Every so often the gantry would not start: during rotor initialization the log showed RMC NO ZERO GATE, and the index LED on the ghost board stayed dark as the flag passed the optical sensor.
What was checked
- Replaced the board carrying the optical zero-gate sensor — no change.
- Continuity-tested the wiring from the sensor to the DMC — no fault found.
- Swapped the DMC — the fault persisted.
- Compared signal timing in the logs and the error report; the engineers found the index LED gave no pulse when the flag went by.
Cause
The zero gate flag was mounted slightly out of position: its pass did not line up in time with the northmark pulse from the resolver, so the RMC read no valid zero gate even though the sensor, wiring and DMC were healthy.
What was done
The engineers repositioned the zero gate flag so its pass coincided with the resolver's northmark pulse, confirmed the timing in the logs, and the gantry started reliably again.
Safety
Before reaching into the gantry, let the rotor spin down completely and secure it against rotation, and repeat the electrical safety tests before the scanner goes back into use.
Lesson: An intermittent signal-missing fault from a position sensor can be pure mechanics — check flag alignment and timing against the reference pulse before replacing boards.
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.