Siemens Symphony: optical link down for gradient coil temperature monitoring
What happened
On a Siemens Symphony MRI the optical link from D9 PTAB to D17 GSSU, which carries gradient coil temperature data, stopped passing a signal: light was still visible in the fiber, but the receiving end did not trigger. Gradient coil temperature monitoring was temporarily down (as reported in the case).
What was checked
- Swapped in a spare D9 module and a spare optical cable to rule out both.
- Checked the spare fibers of the optical cable as alternate paths (seven, as reported in the case).
- Measured the transmitter output with an optical power meter and compared the value with the datasheet.
- Swapped the optical transmitters between positions to see whether the fault follows the part.
Cause
Probable: gradual degradation of the optical transmitter's output power with age. The engineers found that a visible glow in the fiber says nothing about the power actually arriving at the receiver; a similar reported case was cleared by replacing the emitter.
The cause is probable and was not fully confirmed.
What was done
First step was to swap the emitters in D9 to confirm the fault follows the part; if it does, replace the optical transmitter — reportedly a standard part available off the shelf. The repair restores the monitoring channel instead of leaving it disabled.
Safety
Gradient coil temperature monitoring is a protection channel, so do not return the scanner to routine clinical use while it is down, and remember the magnet is always energized — only non-ferromagnetic tools in the exam room.
Lesson: A glowing fiber only proves the emitter is alive, not that the link is healthy — measure optical power against the datasheet before replacing cable or receiver.
Covered in the course: MRI 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.