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Power down the entire system and wait 30 seconds before proceeding.

Do not attempt repeated power cycles as this may cause additional damage to control boards.

Open the control cabinet and locate the main CPU board or motherboard containing ROM chips or ROM modules.

Use proper ESD precautions - wear grounding strap and work on anti-static mat.

Visually inspect ROM chips or EPROM modules for physical damage, burn marks, or corrosion on pins and sockets.

Contact Fanuc service immediately with control model and serial number to arrange ROM replacement or complete board exchange. Have machine serial number, control model, and software version ready.

ROM chips are serialized to machine configurations - generic replacements will not work.

Power down completely and discharge residual voltage by pressing and holding power button for 10 seconds while unplugged.

Wait minimum 5 minutes for capacitors to fully discharge before opening control.

Locate ROM modules or EPROM chips on the main CPU board - typically labeled with part numbers starting with A20B or A16B series.

Use proper ESD protection - static discharge can permanently damage ROM chips.

Carefully reseat all ROM modules by removing and firmly reinserting them into sockets. Ensure all pins are properly aligned and fully seated with even pressure.

Do not force modules - bent pins will cause permanent damage. Verify pin alignment before applying pressure.

Clean socket contacts with electrical contact cleaner if corrosion is present. Power up system and observe if alarm clears. If alarm persists, ROM replacement is required.

With system powered down, measure DC power supply voltages at the main CPU board using a multimeter. Check +5VDC, +24VDC rails against specifications in electrical manual.

Verify correct voltage measurement points in manual - incorrect probe placement can short circuits.

Inspect power supply unit for swollen capacitors, burn marks, or unusual odors indicating component failure. Check all fuses related to CPU board power.

If power supply voltages are out of specification or unstable, replace power supply module before condemning ROM or CPU board.

Use only Fanuc-approved replacement power supplies - voltage ripple specifications are critical for ROM operation.

If power supply is verified good and reseating ROM modules does not resolve alarm, the main CPU board requires replacement. Contact Fanuc for board exchange with system backup parameters ready for restoration.

Perform full parameter and program backup before board replacement if system allows access to backup functions.