Siemens Definition AS (PHS4 table): position lost at boot, erratic tabletop jamming
What happened
On power-up the table position showed N/A on the display; after a position calibration the reading came back, but was lost again at the next reboot. Later, after the encoder battery was replaced, a new fault appeared: the tabletop deck stuttered and jammed at random points during travel, and at each jam the motion buttons went inactive.
What was checked
- Table position calibration — the reading was restored, but only until the next reboot
- Encoder battery replaced — position loss stopped, but jamming appeared afterwards
- Bearings and guide rails inspected — mechanics reported in order
- Table moved manually with power off to rule out mechanical binding
- Position readout on the display monitored during motion to track the dropouts
Cause
The engineers found a faulty table position encoder: it first lost the stored position at power-off, then produced erratic feedback that the drive interpreted as an obstruction, causing the random jamming and button shutdown.
What was done
Encoder replaced, then the table position recalibrated using a procedure from the manufacturer's service documentation, done by authorised personnel. In the reported case the position display stayed stable and travel became smooth; the case was closed as solved.
Safety
A patient table is a driven mechanism carrying a moving load: isolate power before working near the drive, keep hands clear of pinch points under the deck, and before return to use check the full travel and the stop/inhibit functions with no patient on the table.
Lesson: When position data is both lost after power-off and erratic during motion, suspect the position feedback device itself before overhauling the mechanics — and re-test the full table travel after any encoder work.
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.