FCM Bars Renex: power-on board failure and lost console link
What happened
On an X-ray unit the power-on (start-up) board went dead. After it was reworked, the console kept reporting a power-on module error and received nothing over the RS232 link, although the power-on relay output showed 24 V, as reported in the case, and the columns travelled up and down normally.
What was checked
- Visual inspection of the power-on board: the engineers found two blown diodes and a bulged DC-DC converter, as reported.
- Measured 24 V at the power-on relay and confirmed the columns still move.
- Checked the RS232 console link end to end: cable, external RS232-to-USB level converter and COM port settings on the PC.
- Suspected the MAX-series RS232 transceiver ICs on the board were also damaged by the same surge and flagged them for testing and replacement; the console firmware version was also to be verified.
- Confirmed the red emergency stop button was released.
Cause
In this case the surge that killed the diodes and the DC-DC converter most likely also damaged the RS232 transceiver ICs, and possibly the relay, on the same board. The engineers linked it to connecting the control cable through an unsuitable COM/USB converter or port that puts wrong voltage levels on the interface.
The cause is probable and was not fully confirmed.
What was done
The engineers reworked the board: replaced the blown diodes, the DC-DC converter and the optocouplers. After that the relay voltage returned and the columns worked, but the console error stayed. Replacing the RS232 transceiver ICs and the relay on the board was recommended, along with a proper level converter, a check of the released emergency stop button and of the COM port settings. The outcome is described as probable, not yet fully confirmed.
Safety
Before any board-level work isolate the unit from the mains and verify that internal capacitors are discharged, and before return to use run electrical safety checks plus a functional check of the X-ray interlocks and the emergency stop.
Lesson: When a control board dies from a surge on the interface, treat every IC on that line as suspect and verify the whole console link chain — cable, converter, transceivers, settings — before declaring the unit repaired.
Covered in the course: X-ray 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.