238-101B

Check acceleration parameters

Navigate to MOD > Machine Parameters > Axis-specific parameters and verify acceleration/deceleration values for affected axes are within manufacturer specifications.

Reduce deceleration rates by 20-30% initially to test if alarm clears

Inspect regenerative resistor circuit

Verify regenerative brake resistor connections and resistance values match UVR power supply specifications. Check for burnt or damaged resistors.

Ensure power is OFF and capacitors are discharged before checking resistor circuits

Monitor DC-link voltage during operation

Use TNC diagnostic screen to monitor real-time DC-link voltage values during normal machining cycles to identify voltage spike patterns.

Access via PLC > Status > Drive diagnosis for real-time voltage monitoring

Check UVR status LEDs

Examine UVR power supply unit status indicators for fault conditions. Red LEDs typically indicate internal faults requiring unit replacement.

Do not attempt internal UVR repairs - unit contains high voltage components

Measure input voltage stability

Verify incoming AC line voltage is stable and within UVR specifications (typically ±10% of nominal). Use calibrated multimeter at UVR input terminals.

Check for voltage fluctuations during high-load machining operations

Review UVR error history

Access TNC error log via MOD > Service > Error messages to check for recurring UVR-related alarms indicating progressive component failure.

Pattern of increasing frequency suggests imminent UVR replacement needed

Verify motor parameter settings

Check MOD > Machine Parameters > Drive parameters to ensure motor specifications match actual installed motors, particularly rated voltage and current values.

Mismatched motor parameters can cause drive system to generate unexpected voltage levels

Review power supply configuration parameters

Validate UVR-specific parameters in machine parameter list, including DC-link voltage limits and regenerative energy handling settings.

Only modify power supply parameters with original machine documentation

Compare with backup parameter set

Load known-good machine parameter backup via MOD > Machine Parameters > Load parameters to eliminate configuration-related causes.

Always create parameter backup before making changes for easy rollback

Install power quality monitor

Connect power quality analyzer to main electrical feed to record voltage fluctuations, harmonics, and transients over 24-hour period.

Focus monitoring during peak facility power usage times

Check facility power distribution

Verify machine is connected to appropriate electrical service with adequate capacity and proper grounding per Heidenhain installation requirements.

Ensure qualified electrician performs electrical system evaluation

Consider power conditioning equipment

Evaluate installation of voltage regulators or uninterruptible power supply if grid power quality issues are confirmed.

UPS systems can eliminate most power quality issues affecting CNC operation

Measure capacitor bank voltage

Use appropriate high-voltage meter to check DC-link capacitor voltage levels and ripple content during operation.

DC-link capacitors retain lethal voltage even after power shutdown - use proper safety procedures

Perform capacitor ESR testing

Test equivalent series resistance of DC-link capacitors using specialized ESR meter to identify degraded capacitors requiring replacement.

High ESR values indicate capacitor aging and reduced filtering effectiveness

Check capacitor physical condition

Visually inspect DC-link capacitors for bulging, leakage, or other physical damage indicating failure.

Replace entire capacitor bank if any individual capacitor shows signs of failure