239-0122

Verify Fan Operation

Open the electrical cabinet and visually/audibly confirm all FSUC cooling fans are running. Check fan power supply voltage at fan connectors (typically 24VDC or 230VAC depending on configuration). Fans should activate whenever NC power is on.

Disconnect main power and follow lockout/tagout procedures before opening electrical cabinets. Wait 5 minutes for DC bus capacitors to discharge.

Inspect Airflow Path

Remove and clean all air intake filters on FSUC cabinet. Inspect heatsink fins on FSUC unit for dust buildup and clean with compressed air (max 3 bar pressure). Verify cabinet ventilation slots are not blocked by cables or external obstructions.

Heavy dust accumulation typically indicates inadequate shop air filtration. Consider installing additional filtered intake vents or relocating cabinet away from grinding/sanding operations.

Check Thermal Imaging

If available, use thermal camera to inspect FSUC heatsink temperatures during operation (compare left/right sides for uniform heat distribution). Hot spots indicate potential failed IGBT modules or poor thermal coupling.

Normal operating temperature for FSUC heatsinks under moderate load is 50-65°C. Temperatures exceeding 75°C with fans running indicate cooling system inadequacy or component failure.

Access Temperature Monitoring Parameters

Enter MOD mode, select 'Spindle Parameters', navigate to machine parameters MP7710.0 (temperature monitoring type) and MP7711.0 (temperature threshold). Verify sensor type matches motor specification (0=none, 1=KTY84, 2=PT1000, 3=PTC thermistor).

If MP7710.0 is set incorrectly for the actual sensor type installed, the FSUC will misinterpret resistance values as extreme temperatures.

Measure Sensor Resistance

Disconnect motor temperature sensor leads at FSUC X722 or motor terminal box. Using precision multimeter, measure resistance: KTY84 should read 1000Ω±5% at 25°C, PT1000 should read 1000Ω at 0°C (1100Ω at 25°C). Readings outside range indicate failed sensor.

Ensure spindle motor has cooled to ambient temperature before resistance measurement for accurate diagnosis.

Inspect Sensor Wiring

Check continuity and insulation resistance of temperature sensor cable from motor to FSUC connector. Look for cable damage at motor cable carrier entry points. Verify shield connection is intact and grounded only at FSUC side per Heidenhain wiring standards.

Temperature sensor cables routed too close to spindle motor power cables can pick up EMI causing erratic readings. Maintain minimum 100mm separation or use separate cable carrier.

Bypass Test (Diagnostic Only)

Temporarily set MP7710.0=0 (temperature monitoring OFF) to disable sensor monitoring. If machine runs normally without 122 alarm, confirms sensor/wiring fault rather than actual thermal problem. Return to proper monitoring after diagnosis.

Operating with temperature monitoring disabled removes critical motor protection. Use only for short diagnostic tests with reduced spindle loads. Never run production with monitoring disabled.

Review Spindle Load History

Access PLC diagnostic screens or use Heidenhain's Data Transfer software to retrieve FSUC load history if available. Check recent programs for continuous high-feedrate operations, excessive DOC (depth of cut), or tool dulling requiring higher spindle torque.

The FSUC records maximum current events. In MOD, check spindle diagnostic values - sustained operation above 80% rated current indicates loading issues.