Siemens gradient amplifier 781: repeated amplifier burnouts
What happened
As reported in the case, two gradient amplifiers burned out within two months; before that, the gradient had been shutting down on a single axis due to overheating.
What was checked
- Determine whether the failed gradients were on the same axis or on different axes.
- Scan the amplifier with a pyrometer during a scan to find a channel running hot.
- Keep in mind that the flow sensor measures total flow, so a blocked single channel may still read normal.
- Inspect the cooling hose distributor (single top input with four hoses: three amplifiers and the power supply); in this case the Y-channel was blocked.
Cause
The engineers found a cooling flow blockage in the Y-axis channel of the hose distributor; the flow sensor read normal because it measures only the total flow.
The cause is probable and was not fully confirmed.
What was done
The outcome in this case was probable rather than confirmed: the recommendation was to flush the per-axis cooling circuits before installing replacement amplifiers (281/271, as reported) and to monitor the amplifier with a pyrometer during scans.
Safety
Before working inside the amplifier, isolate the power and let internal capacitors discharge per the manufacturer's service procedure, and confirm cooling flow to every channel before the system is returned to use.
Lesson: A normal total-flow reading can hide a blocked single-channel cooling path, so check temperature and flow per axis before condemning an amplifier.
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.