916

Power down the CNC completely and wait 5 minutes. Remove all axis motor power cables and I/O connections to eliminate external noise sources. Reseat the main CPU board in its slot ensuring proper connector engagement.

Ensure proper ESD grounding procedures before handling CPU board. Disconnect all power sources including battery backup.

Power up and observe if alarm recurs immediately during boot sequence. If alarm persists before reaching System screen, the DRAM hardware is confirmed defective.

Access MAINTENANCE > SYSTEM > PMC MEMORY or DIAGNOSIS screen to check for additional memory-related alarms (915, 917, 918 series). Document all displayed errors for Fanuc service.

Replace the main CPU board assembly with a compatible spare. After installation, initialize parameters from backup using SYSTEM > I/O CHANNEL and restore all parameter sets (000-9999), PMC ladder, and macro programs.

Replacing CPU board requires system reinitialization. Ensure complete parameter backup exists before proceeding. Board must match control series and software version.

Using a digital multimeter, measure the +5VDC, +24VDC, and ±15VDC power supply outputs at the power supply unit test points. Verify +5VDC is within 4.85-5.15VDC under load with minimal ripple (<100mV).

Measurements must be taken with power on. Use extreme caution around live circuits.

Inspect all grounding connections between control cabinet, machine frame, and incoming power earth ground. Verify ground impedance is below 0.1 ohms using a ground resistance tester.

Check for nearby sources of electromagnetic interference such as welders, motor starters, or VFDs. Route CPU board signal cables away from high-current power cables. Install ferrite cores on I/O cables if needed.

If alarm occurs intermittently, replace the power supply module (PSM) feeding the main CPU board. Test with a known-good power supply if available before ordering replacement.

Power down completely and remove main CPU board from control. Visually inspect for physical damage, burnt components, corrosion, moisture contamination, or cracked solder joints around DRAM chips and nearby components.

Use proper ESD protection. Document serial numbers and board revisions before removal.

Check control cabinet cooling fans and air filters. Verify cabinet temperature stays below 45°C (113°F). Clean all filters and confirm adequate airflow across CPU board area.

If moisture or contamination is found, clean board with electronics-grade isopropyl alcohol (99%) and allow to dry completely for 24 hours before reinstallation.

Never apply power to contaminated boards. Severe contamination requires professional board cleaning or replacement.

If physical damage is evident or cleaning does not resolve the alarm, replace the main CPU board and implement environmental controls (sealed cabinet, air conditioning, vibration isolation).