251-0E36

Check encoder cable connections

Inspect all encoder cable connections at motor and TNC input modules. Verify proper shielding and cable routing away from power cables.

Power down system before checking connections to prevent damage

Verify reference mark signals in MOD function

Access Setup > MOD Functions > Encoder Test and monitor the R signal during manual axis movement. The R signal should pulse once per encoder revolution.

Use oscilloscope on encoder inputs if TNC diagnostics show intermittent R signals

Check encoder supply voltage

Measure encoder supply voltage at TNC terminals. Should be 5V ±0.25V for TTL encoders or per encoder specifications for 1Vpp types.

Perform encoder signal quality test

Use TNC encoder test function to verify signal amplitude and phase relationships. A and B signals should be 90° phase shifted with proper amplitude.

Verify reference point parameters

Check MP1010 (reference point approach) and MP1020 (reference cam direction) settings for the affected axis in Setup > Machine Parameters.

Compare settings with working axes or original machine documentation

Check encoder type parameters

Verify MP3010 (encoder input assignment) and MP3020 (encoder resolution) match the actual encoder specifications installed on the machine.

Validate reference mark evaluation

Check MP1030 (reference mark evaluation) setting. Should typically be set to 1 for standard reference mark detection during reference run.

Test reference run sequence

Perform manual reference run in Setup > Reference Points and observe the sequence. The axis should decelerate when reference mark is detected.

Check servo drive status LEDs

Verify all servo drive status indicators show normal operation (typically green). Red or flashing LEDs indicate drive faults that must be cleared first.

Verify EnDat/SSI communication

Check encoder communication status in Setup > MOD Functions > Drive Diagnostics. EnDat or SSI communication errors will prevent proper reference trace operation.

EnDat communication errors often show as intermittent position feedback faults

Check drive parameter consistency

Verify servo drive parameters match TNC machine parameters, especially encoder resolution and reference point settings.

Test drive enable sequence

Cycle servo enable on/off and verify proper handshaking between TNC and drives during reference point approach.

Perform TNC system restart

Execute complete power cycle of TNC control. Allow full boot sequence and check if alarm persists after restart.

Ensure all programs are saved before power cycling

Check TNC software version

Verify current software version in Setup > MOD Functions > Software Options. Check Heidenhain website for known issues with current version.

Clear alarm memory and logs

Clear alarm history in Setup > Service > Clear Alarms and perform fresh reference run to isolate the issue.

Backup and restore system files

Create system backup and consider restoring from known good backup if available. Check system file integrity in MOD functions.

Always maintain recent system backups before making parameter changes