231-8BB0

Access encoder diagnostics

Navigate to MOD → Service → Encoder → Select affected axis to view temperature sensor status and raw values.

Normal KTY84 resistance at 20°C should be around 990-1010 ohms

Check sensor wiring at motor connection

Power down system and inspect KTY84 sensor wires (typically pins 8-9 on motor connector) for shorts, damaged insulation, or moisture ingress.

Always lock out power and verify zero energy state before opening motor connections

Measure sensor resistance

Disconnect sensor wires and measure resistance across KTY84 terminals. Should read 990-1010Ω at room temperature, not near zero ohms.

If reading near zero ohms, sensor or wiring is shorted

Verify cable routing

Check that temperature sensor cables are routed away from power cables and not pinched in cable carriers or motor mounting.

Temperature sensor cables should have separate shielding from encoder signal cables

Verify sensor type in machine parameters

Check MP7440 TEMP_SENS_TYPE is set to 1 for KTY84 sensor type on the affected axis.

MP7440 must match actual sensor installed - incorrect setting causes false alarms

Test sensor with known good unit

Replace suspected KTY84 sensor with known good sensor and monitor temperature readings in encoder diagnostics.

Ensure replacement sensor is genuine KTY84-130 type, not KTY83 or other variants

Check sensor mounting and thermal contact

Verify KTY84 sensor is properly seated in motor housing with good thermal contact using appropriate thermal compound.

Poor thermal contact can cause delayed or inaccurate temperature readings

Monitor temperature trend

Run axis movement and observe temperature rise in MOD → Service → Encoder diagnostics to confirm sensor responds to actual temperature changes.

Healthy KTY84 should show gradual temperature rise during axis movement

Check encoder board status LEDs

Inspect encoder input board for error LEDs and verify board part number matches machine configuration in MP1010.

Red LEDs on encoder board typically indicate hardware faults

Swap encoder channels for testing

If multiple axes available, swap encoder connections to isolate whether fault follows motor or stays with encoder input channel.

Document original connections before swapping and ensure axis parameters match

Verify encoder board supply voltages

Measure +5V, +15V, and -15V supply voltages at encoder board test points per Heidenhain service manual specifications.

Temperature measurement circuits are sensitive to supply voltage variations

Check for electromagnetic interference

Verify encoder board shielding is intact and all cable shields are properly terminated to avoid EMI affecting temperature circuits.

EMI can cause erratic temperature readings that appear as sensor faults

Verify sensor part number

Confirm installed sensor is KTY84-130 type by checking part markings on sensor body or motor documentation.

KTY83 sensors have different resistance curves and will cause temperature errors

Check temperature monitoring parameters

Verify MP7441 TEMP_LIMIT_MAX and MP7442 TEMP_LIMIT_MIN are set to appropriate values (typically -20°C to +120°C for KTY84).

Overly restrictive temperature limits can cause nuisance alarms

Review encoder configuration

Check MP1013 encoder type matches actual encoder model and supports temperature monitoring functionality.

Some older encoders don't support temperature monitoring - check encoder nameplate