160-00B9

Check alarm text for overvoltage indication

Read the complete alarm message where '%1' is replaced. Look for terms like 'DC_OVERVOLTAGE', 'Vdc too high', or voltage values exceeding 750VDC. Note the exact wording for module identification.

If alarm occurs consistently during Z-axis retract or rapid traverse deceleration, regenerative braking is almost certainly the cause.

Verify braking resistor circuit integrity

With power off and locked out, measure braking resistor resistance (typically 10-50 Ohms depending on system). Check all connections to the resistor and verify chopper transistor gate drive signals with oscilloscope during controlled testing if possible.

Braking resistors may remain hot for 30+ minutes after operation. Allow cooling time and verify temperature before touching.

Test with reduced acceleration parameters

Temporarily reduce axis acceleration and jerk settings in MP1200-MP1299 (axis-specific dynamics) by 50% and retest. If alarm clears, the braking system is undersized or faulty.

Check MP1810 (braking resistor monitoring) and MP1811 (braking power limit) settings - these must match the installed hardware specifications.

Inspect power supply braking chopper module

Locate the braking chopper (often integrated in PSL or as separate PD module). Check LED status and measure DC bus voltage under controlled deceleration using the drive system's voltage monitoring in MOD > Service > Diagnosis.

On iTNC 530 and TNC 620 systems with HMV drives, the chopper activation threshold is typically set at 750VDC - verify this matches your incoming line voltage specifications.

Measure incoming line voltage at cabinet

With power applied, measure L1-L2, L2-L3, and L3-L1 voltages at the main disconnect. All readings should be within 2% of each other (e.g., 395-405V for 400V nominal). Also verify L1-PE, L2-PE, L3-PE are balanced.

Lethal voltage present. Only qualified electricians should perform measurements on incoming mains power.

Check input contactor and fuse integrity

Inspect main contactor K1 (or similarly labeled mains contactor) for burned contacts or coil failure. Verify all three poles close simultaneously. Check all incoming fuses for continuity - a single blown fuse creates phase loss.

Listen for contactor chatter or abnormal buzzing when closing - this indicates low coil voltage or mechanical wear causing contact bounce.

Review DC bus voltage trend in error log

Access MOD > Service > Error Messages and check the timestamp of the alarm. Then check MOD > Service > Diagnosis > Power Supply for stored voltage min/max values. Phase loss causes DC bus to drop below 450VDC on 400V systems.

If DC bus voltage shows cyclic variation (e.g., 500-650VDC oscillation at 50/60 Hz rate), this confirms single-phase operation.

Verify utility power quality at source

If cabinet-level measurements are acceptable, install a power quality analyzer for 24-48 hours to capture transient events. Check for voltage sags, swells, or momentary interruptions that coincide with alarm occurrences.

Heidenhain controls have tight tolerance for power quality - consider adding line conditioning or isolation transformer if facility power is consistently marginal.