239-0006

Verify Supply Voltage at Drive Input

Measure L1, L2, L3 voltage at the main drive power terminals with machine under typical load. Record all three phase-to-phase voltages and verify balanced within 2% and within nameplate range (typically 380-480VAC ±10%).

Only qualified electricians should work on line voltage. Disconnect main power and verify zero voltage before accessing terminals.

Check PLC Supply Monitoring

Navigate to MOD 9 3 (PLC Diagnostics) and select drive system monitoring. View real-time DC bus voltage reading - normal operating range is 530-750VDC for 400VAC supply. Note whether voltage drops correlate with axis motion or other machine events.

Use the trace function in diagnostic screen to capture voltage behavior during the alarm event - look for voltage dips during spindle acceleration or when multiple axes move simultaneously.

Inspect Supply Contactor and Connections

Check main supply contactor K1 contacts for pitting, burning, or wear. Verify all power terminal connections are tight (retorque to specifications). Loose connections cause voltage drop under load and can trigger this alarm during high current draw.

Disconnect and lockout main power before inspecting connections.

Test Under Load Conditions

With voltage monitoring active, run a test program that includes rapid acceleration/deceleration and full spindle load. Observe if alarm occurs at consistent machine events indicating supply inadequacy versus random occurrence suggesting component failure.

If voltage drops only during specific machine operations, the supply may be undersized or shared with other heavy loads causing brown-out conditions.

Check UM Module Operating Hours

Access Service menu and review power-on hours for the affected UM module. DC link capacitors typically require replacement at 40,000-60,000 hours depending on ambient temperature. Navigate to PLC > System Info > Component Hours to verify.

Capacitor life halves for every 10°C increase in operating temperature - check cabinet cooling system effectiveness.

Review DC Bus Voltage Ripple

In MOD 9 3 drive diagnostics, enable ripple voltage monitoring if available on your TNC generation. Excessive ripple (>10% of nominal DC voltage) indicates capacitor degradation. Compare ripple values between different UM modules if multiple installed.

On 640 and newer controls with advanced diagnostics, the CapCheck function can estimate remaining capacitor life percentage.

Perform Visual Inspection of UM Module

With power disconnected, open the UM module housing and visually inspect DC link capacitors for bulging tops, electrolyte leakage, or discoloration. These are clear indicators of end-of-life condition requiring module replacement or capacitor service.

Wait minimum 10 minutes after power disconnect for capacitor discharge. Verify zero voltage with meter before touching components. DC bus capacitors store lethal voltage.

Replace UM Module or Service Capacitors

If capacitor degradation confirmed, replace entire UM module (recommended) or have qualified technician replace individual DC link capacitors with Heidenhain-approved components. After replacement, run full diagnostic test cycle and recalibrate FSUC monitoring parameters if required.

Keep old module for emergency spare after capacitor replacement - document service date and reset hour counter in PLC maintenance log.

Check Regenerative Resistor Resistance Value

Disconnect regenerative resistor circuit and measure resistance with ohmmeter. Verify measured value matches nameplate specification (typically 20-50 ohms depending on drive size). Open circuit or significantly increased resistance indicates burnt resistor element.

Ensure resistor has cooled completely before handling - surface temperature can exceed 200°C during operation.