239-0113

Check Braking Resistor Configuration

Access machine parameter list and verify braking resistor parameters are correctly configured for your UM-FSUC module. Check parameters related to brake chopper enable, braking resistor value (ohms), and power rating (watts).

Heidenhain UM modules typically require braking resistor parameters to be configured in the drive-specific parameter sets, not the main machine parameters.

Measure Braking Resistor Continuity

Power down the control cabinet completely. Disconnect the braking resistor from the UM module terminals and measure resistance with an ohmmeter. Compare against the resistor's nameplate value (typically 30-100 ohms for spindle applications).

Allow at least 10 minutes after shutdown for DC bus capacitors to discharge before touching any power components.

Inspect Brake Chopper Circuit

Verify the brake chopper LED indicator on the UM-FSUC module (if present) activates during spindle deceleration. Access UM diagnostics via PLC to check brake chopper activation status and duty cycle during operation.

If brake chopper shows 100% duty cycle during alarm occurrence, the resistor capacity is insufficient for the deceleration profile being used.

Monitor Supply Voltage at Control Cabinet Input

Using a true RMS multimeter or power quality analyzer, measure all three phases of incoming AC voltage at the main disconnect terminals. Record voltage during normal operation and during alarm occurrence. Check for variations exceeding ±10% of nominal voltage.

High voltage measurement - only qualified electricians should perform this test with proper PPE and voltage-rated test equipment.

Check Phase Balance

Measure voltage between all three phase combinations (L1-L2, L2-L3, L3-L1) and verify phase balance within 2% of each other. Significant imbalance causes DC bus ripple and can trigger voltage alarms.

Also check each phase to ground - asymmetrical grounding issues can cause voltage reference problems in the UM module.

Review PLC Error Log for Correlation

Access MOD function and navigate to the PLC error log. Check timestamps of alarm 239-0113 occurrences and correlate with any other electrical alarms or external events (machine tool events, other equipment starting/stopping on same supply).

Heidenhain controls timestamp all alarms - pattern analysis can reveal if voltage errors coincide with specific machine operations or external facility events.

Access UM Module Diagnostic Display

Enter PLC Programming mode (MOD 33) and navigate to the UM-FSUC diagnostic page. Read the actual DC bus voltage value displayed and compare against expected value (typically 1.35 x AC line voltage for 3-phase rectification). Record this value.

Normal DC bus voltage for 400VAC supply should be approximately 540VDC; for 480VAC supply approximately 650VDC under no-load conditions.

Verify Voltage at UM Test Points

With control powered, carefully measure DC bus voltage at the UM module's designated test points using a voltage-rated multimeter. Compare actual measured voltage against the diagnostic display value from Step 1.

DC bus voltage can exceed 800VDC. Use properly rated test equipment and extreme caution. Do not bridge test points with probes.

Check UM Module Firmware and Configuration

Access system settings and verify UM-FSUC firmware version. Check if voltage threshold parameters (overvoltage limit, undervoltage limit) are set to appropriate values for your supply voltage. Default values may be incorrect for your installation.

Heidenhain service tools can display configured voltage thresholds - typical overvoltage threshold is 800VDC, undervoltage threshold is 380VDC for standard 400VAC systems.