Class 769 – Fire Control Unit Failures

Reported Issue

After long periods without power (1–3 months), the Fire Control Unit would fail catastrophically on first power-up, preventing train start.

Initial Observations

• Units were previously repaired by replacing internal components without identifying root cause.

• Multiple failed units were supplied showing similar damage patterns.

Investigation

• Full strip-down and component-level analysis conducted.

• Partial schematics obtained (original manufacturer (BRUSH) no longer exists).

• Power consumption and processor behaviour validated against datasheets.

• Failure evidence aligned with cable discharge / triboelectric effects during re-energisation.

Root Cause

• Overvoltage transients caused by stored charge in long cable runs.

• Discharge events exceeded component tolerance during initial power-up.

• Industry standards for cable discharge testing confirmed relevance.

Resolution

• A dedicated overvoltage suppression module was designed.

• All signals routed through the protection circuit.

• Design refined following simulation and component selection.

• PCB layout and SPICE simulation underway.

• EFT and capacitive clamp testing planned using in-house equipment.
  
  

Outcome

• Root cause conclusively identified.

• Preventative design solution implemented