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Troubleshooting the Bridge Fault on APEX Products

The "Bridge Fault" LED on an Apex drive or drive/controller indicates that the internal drive FETs
- the circuitry that controls power generation - has been exposed to an excessive over-current or over-temperature condition. If this fault LED is illuminated, it may be cleared by coupling the RESET pin to the GND pin for approximately one or two seconds, then uncoupling it. These pins are located on the front panel of the Apex unit. If the "Bridge Fault" LED does not turn off, then the FETs have probably been damaged to the point that the Apex unit must be sent in for repair.

Also, be sure to measure the resistance between each of the phases of the motor being powered by the APEX drive, as a motor winding short can cause the "Bridge Fault" LED to illuminate as well. Measure the resistance between the following motor wires or pins:

  • Phase A and Phase B
  • Phase B and Phase C
  • Phase C and Phase A

    If the measured resistance between these windings are not all nearly identical (+/- 5%), or if one or more resistance measurements is substantially lower than the other(s), then the motor needs to be replaced, as it is the likely cause for the Bridge Fault on the Apex product. Contact the Compumotor Applications Department at 1-800-358-9070 to verify.