Siemens Avanto: PALI fault on all coils except the knee coil
What happened
A periodic PALI error appeared on all coils except the knee coil. The RF characteristics test failed at step 4: with the TAS 50-ohm load connected, the amplifier reportedly jumped straight to full output power (a value of about 12200 as reported in the case), ramped it down, and was cut off on the first iteration.
What was checked
- Swapped in a known-good TAS to rule out the load.
- Walked the modulator–RFPA–TAS–BCCS–TALES–body coil chain through the first three steps of the test.
- Checked the TALES voltages through the test routines, not by manual probing (as done in the case).
- Re-ran the Tune Up / RF characteristics test after each step.
- Reviewed the error log and test reports to see the fault pattern.
Cause
The engineers found a faulty RFSU power supply — not the RF amplifier or the TAS that were suspected first. Its degraded output pushed the amplifier into the reported full-power behaviour, which the system tripped as PALI.
What was done
The RFSU power supply was ordered and replaced promptly. The fix was done per the manufacturer's service documentation by authorised personnel; after the replacement the PALI errors stopped and the RF characteristics test passed.
Safety
Before opening the RF cabinet, isolate and lock off the supply, allow the power-supply capacitors time to discharge and verify zero voltage — and take only non-ferromagnetic tools into the magnet room.
Lesson: When a fault hits every coil except one, suspect the shared supply feeding the chain before condemning the 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.