919

Power down the CNC completely. Disconnect AC input power and wait 5 minutes for all capacitors to discharge before opening the control cabinet.

Always follow LOTO procedures. Residual voltage can remain on boards even after power-down.

Inspect the main CPU board (mounted in the control unit) for physical damage, burn marks, or bulging capacitors near the DRAM ICs. Check for proper board seating in the backplane connector.

Reseat the main CPU board firmly in the backplane. Power up and observe if alarm recurs immediately during boot or intermittently during operation.

If alarm persists, replace the main CPU board (part number specific to your control series: 0i-F, 31i-B5, 32i, etc.). After replacement, reload system parameters from backup via SYSTEM > PMC > LADDER or from CF/USB card.

Ensure you have a complete parameter backup before board replacement. Loss of parameters will require machine re-commissioning.

Check the power supply unit (PSU) DC voltages on the CPU board connector. Use DIAGNOSIS > DC VOLTAGE screen (if available on your series) or measure directly: +5V, +24V, ±15V rails should be within ±5% tolerance.

Measure voltages with control powered and under load conditions if possible.

Inspect grounding connections between the control cabinet frame, machine bed, and AC input ground. Verify ground resistance is less than 0.1 ohms. Check for loose ground lugs or corroded connections.

Review recent electrical environment changes: new equipment on shared circuits, welders, induction heaters, or VFDs nearby. Install line filters or isolation transformers if excessive noise is detected.

If PSU output voltages are unstable or noisy, replace the power supply module. After replacement, monitor for alarm recurrence over several hours of operation.

Check control cabinet internal temperature. If cooling fans are obstructed or failed, measure ambient temperature near CPU board. Should not exceed 55°C (131°F) during operation.

Inspect all cooling fans in the control cabinet. Verify airflow direction (typically bottom intake, top exhaust). Replace failed fans and clean intake filters if clogged with coolant mist or debris.

Examine CPU board for signs of corrosion, moisture intrusion, or metallic dust bridging between traces. Clean with electronics-grade contact cleaner and compressed air if contamination is present.

Never use water or general-purpose cleaners on electronic boards.

If environmental conditions are addressed but alarm persists, the DRAM damage is permanent. Proceed with CPU board replacement as described in Cause Block 1.