The FANUC A20B-3900-0302 is a plug-in FROM/SRAM system memory module for compatible FANUC CNC control units. FROM stores control and user software, while SRAM provides battery-backed storage for CNC data.

This is a system-specific module, not a general-purpose RAM card. Replacement requires matching the part number, revision, host main board, software and machine options. Common boards are marked A20B-3900-0302/01A; order by the complete number on the actual module.

A20B-3900-0302 Product Information

FROM and Battery-Backed SRAM Functions

FROM retains CNC control and user software without normal operating power. SRAM depends on battery backup and holds data required by the configured CNC. A damaged module, failed backup circuit or corrupted data may cause startup, SRAM or software alarms; diagnosis should also cover the battery, main board and power supply.

Compatibility and Capacity Verification

A20B-3900-0302 is documented as a FROM/SRAM module for newer FANUC i-Series control hardware. Public listings disagree about its capacity, so no unverified value is stated. Confirm A20B-3900-0302, revision /01A when present, control series, CPU/main-board number, software edition and options. A20B-3900-0300, -0301 and -0303 are not automatic substitutes.

Backup, Testing and Installation

REACO CNC checks the label, connector, components, physical condition and applicable memory recognition before shipment. Back up parameters, programs, offsets, PMC data and other machine information before removal. FANUC documentation states that system software must be installed when a FROM/SRAM module is replaced, so qualified CNC personnel should handle replacement and restoration.

Related resources: FANUC CNC circuit boards, FANUC CNC controls and FANUC CNC repair services.