231-C690

Identify Affected Axis

Note the axis designation from the %1 parameter in alarm 231-C690. Cross-reference this with the machine's electrical documentation to locate the specific drive module and cable routing.

The %1 parameter often shows the logical axis name (X, Y, Z, etc.) but may show the physical drive number depending on TNC version.

Inspect Cable Connections

Power down the control and check the EnDat/drive communication cable at both ends - X116/X126 connectors on the TNC side and the corresponding connector on the drive module. Look for bent pins, contamination, or loose retention clips.

Always disconnect main power and wait for DC-Bus discharge (minimum 5 minutes) before handling drive connections.

Check Cable Routing and Condition

Inspect the cable along its entire length for pinch points, sharp bends (minimum bend radius 10x cable diameter), or proximity to power cables. Check cable shields are properly terminated at both ends.

Drive communication cables should never be routed in the same cable tray as motor power cables - maintain minimum 200mm separation.

Perform Cable Swap Test

If possible, swap the suspected cable with an identical cable from a functioning axis. If the alarm follows the cable, replace it. Use only Heidenhain-approved shielded cables with correct impedance.

Always use cables with part numbers specified in the drive system documentation - generic industrial cables often lack the required electrical characteristics.

Verify 24VDC Supply Voltage

Using a multimeter, measure the 24VDC supply at the drive module terminals (typically labeled +24V and 0V). Voltage should be 24V ±10% (21.6-26.4VDC) under load with ripple less than 200mV peak-to-peak.

Measure voltage with the system powered and drives enabled to check for voltage drop under load conditions.

Check DC-Bus Voltage

Access Service > Diagnosis > Inverter Status on the TNC control. Verify the DC-Bus voltage for the affected drive shows nominal value (typically 565VDC for 400VAC systems). Low DC-Bus indicates main power supply issues.

DC-Bus voltage below 500VDC on a 400VAC system will cause erratic communication and multiple alarms.

Inspect Power Supply Unit

Check the 24VDC power supply unit for proper operation - verify LED indicators show normal status, check for proper ventilation, and listen for abnormal fan noise indicating thermal stress.

If multiple axes show C690 alarms simultaneously, the common 24VDC supply is the most likely culprit rather than individual drive modules.

Review Current Draw

Measure current draw on the 24VDC supply and compare to the sum of all connected devices. If near maximum rated capacity, the supply may be sagging during peak loads, causing intermittent communication errors.

Add a 20% safety margin to 24VDC supply calculations - drives under rapid acceleration can draw brief current spikes that cause voltage dips.

Perform Drive Module Swap Test

If available, swap the suspected drive module with an identical unit from a working axis. If the alarm follows the drive module to the new position, the drive hardware is defective.

Before swapping drives, record all parameter settings using MOD > System Parameters > Save Parameters to ensure proper configuration restoration.

Check Drive Module Status LEDs

Examine the status LEDs on the drive module itself. A communication error typically shows as red or flashing LED patterns. Consult the drive module documentation for specific LED code meanings.

Many Heidenhain drive systems use a standard LED code: green=OK, yellow=warning, red=fault, flashing red=communication error.