ZirkonZahn ARTI S600: USB link drops when touching the scanner housing
What happened
In one dental lab scanner, touching the housing made the USB link to the PC drop for an instant and reconnect on its own; without touches the connection stayed stable. The case also mentions an earlier failed stepper-driver board with lost manipulator coordinates.
What was checked
- Checked earth continuity from the scanner through to the wall outlet and found the path through the power strip's earth contacts too resistive.
- Checked grounding of the manipulators, power supply and stepper-driver board.
- Swapped the USB cable and inspected the USB socket — no change.
- Ruled the interface/USB controller board and the common-mode choke between the connector and the port chip unlikely, by comparison with similar cases.
- Considered bonding the two housings directly and adding ferrites on the USB line.
Cause
The engineers found a potential difference between the PC case and the scanner case: static charge could not equalise quickly because the only bond between the two ran through high-resistance earth contacts in the power strip outlets. Each touch of the housing discharged through the USB port and momentarily killed the link.
What was done
No board swap and no software involved: the engineers bonded the PC case and the scanner case directly with a reasonably thick conductor (potential equalisation). As reported in the case, the link stopped dropping after that.
Safety
An equalising conductor supplements protective earth and never replaces it: unplug both units before any work, and before return to use verify outlet earth continuity and run the electrical safety checks (earth bond, leakage current) appropriate for the device.
Lesson: If a USB link misbehaves only when someone touches the chassis, suspect earthing and potential equalisation first — check the bond path between housings before blaming the interface electronics.
Covered in the course: Dental Equipment 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.