239-0004

Verify Braking Resistor Circuit

Check the braking resistor and chopper unit connections for the affected axis. Measure resistance value of braking resistor (typically 20-50 ohms depending on system) and verify it matches machine documentation.

Disconnect power and verify zero voltage before measuring resistor values. High voltage DC bus can remain charged.

Monitor DC Bus Voltage During Motion

Access diagnostic display via MOD > System Diagnostics > Power Supply. Monitor DC bus voltage while executing typical rapid deceleration moves. Voltage should not exceed 800VDC on standard 3x400VAC systems.

Use the control's oscilloscope function (if available on TNC 640) to capture voltage spikes that may not appear in standard monitoring.

Adjust Deceleration Parameters

Review and reduce acceleration/deceleration values in machine parameters (MP 1810 and MP 1811 for respective axes) to reduce regenerative energy. Consider increasing deceleration ramps by 20-30% as a test.

Check MP 1860 (maximum axis acceleration) which may override programmed values and cause unexpected rapid stops.

Check PSU Diagnostic LEDs

Inspect the power supply unit for status LEDs. On typical Heidenhain systems, green indicates normal operation, red indicates fault. Document any error codes displayed on the PSU's own diagnostic display if equipped.

Do not open PSU covers while powered. High voltage DC and AC present inside.

Measure DC Bus Voltage at PSU Output

With qualified personnel, measure DC bus voltage at the PSU output terminals (DC+ and DC-). Should be 565-600VDC for 400VAC input systems. Voltage below 520VDC or above 650VDC indicates PSU regulation issues.

Measure voltage both at no-load and under typical machining load. Voltage drop exceeding 30-40VDC under load suggests capacitor bank degradation.

Review PSU Error History

Access control error log via MOD > Service Display > Error Messages. Filter for PSU-related alarms (typically 2xx series). Check for intermittent PSU warnings that preceded this CC voltage error.

Note the %2 parameter in the alarm which identifies the specific CC module number. Cross-reference with machine electrical documentation to determine which PSU circuit supplies that module.

Inspect PSU Capacitor Bank

If PSU is aging (>10 years), visually inspect main DC bus capacitors for bulging, leakage, or discoloration. Capacitor ESR testing by qualified technician can identify degraded capacitors before complete failure.

Capacitors store lethal voltage even after power disconnection. Follow proper discharge procedures per Heidenhain service documentation.

Identify Specific CC Module Number

Note the %2 parameter in alarm 239-0004 which identifies the specific CC module (e.g., CC0, CC1, etc.). Reference machine electrical documentation to determine which axes are controlled by this module.

On multi-axis systems, CC modules are typically numbered sequentially. CC0 is often X-axis, CC1 Y-axis, but always verify against machine-specific documentation.

Access CC Module Diagnostics

Navigate to MOD > System Diagnostics > CC Modules. Select the affected CC module and review all voltage rail readings (typically +24V, +15V, -15V, +5V logic supplies). Compare to specifications in service manual.

On iTNC 530 and TNC 620/640, you can access detailed CC diagnostics including temperature, current draw, and individual voltage rails. Screenshot these values for comparison.

Perform CC Module Isolation Test

Power down system and disconnect motor power cables from the affected CC module only. Power up control. If voltage error persists without motor connected, CC module internal fault is confirmed.

Ensure all enabling signals and emergency stop circuits are tested after reconnection. Document all disconnections.