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Power down the machine completely and disconnect all power sources. Wait 5 minutes for capacitors to discharge.

Always follow lockout/tagout procedures before opening control cabinets.

Open the control cabinet and locate the main CPU board. Visually inspect the ROM chips for physical damage, burn marks, or corrosion.

Use proper ESD protection (wrist strap and grounding) when handling electronic components.

Reseat all ROM chips by carefully removing and reinstalling them in their sockets. Ensure proper orientation and full insertion.

Note chip orientation before removal - incorrect installation will cause permanent damage.

If reseating fails, contact FANUC service for ROM chip replacement or motherboard exchange. Document the control serial number, software version, and exact alarm conditions.

ROM chips are not user-serviceable parts on most modern FANUC controls - unauthorized replacement voids warranty.

With the control powered on but before starting the CNC, measure the DC voltages on the main CPU board: +5VDC, +24VDC, and any other supply voltages. Compare to specifications in the maintenance manual.

Use proper voltmeter safety procedures - measure with insulated probes and avoid shorting test points.

Check input AC power quality at the main transformer. Verify voltage is within ±10% of nominal (200V/220V/400V depending on configuration) and frequency is stable.

Inspect all power supply capacitors on the CPU board and power supply module for bulging, leaking, or discoloration. Replace the entire power supply module if capacitors show signs of failure.

Capacitors may retain charge even after power-off - discharge before handling.

Install a power line conditioner or UPS if input power quality is poor or if voltage sags/spikes are detected. Monitor alarm occurrence after power quality improvement.

Perform a complete power cycle: shut down the CNC, disconnect AC power for 10 minutes, then reconnect and restart. Document if alarm is persistent or intermittent.

Check the CPU board's ambient temperature and cooling system. Clean all cooling fans and heat sinks. Verify cabinet temperature is below 45°C (113°F).

Overheating significantly accelerates electronic component failure.

Inspect the motherboard for physical damage: cracked solder joints, burned components, corrosion, or swollen components near the ROM chips and CPU. Pay attention to connector pins and socketed components.

Do not attempt board-level repairs unless qualified - improper soldering can cause additional damage.

Contact FANUC service for motherboard diagnostics or exchange. Provide control serial number, software version, ladder backup, and parameter backup. Request exchange board with same or compatible ROM version.

Motherboard replacement requires parameter restoration and potentially software reloading - ensure complete backups exist before replacement.