The FANUC A20B-3900-0072 is an 8MB FROM memory module used to store CNC and servo system software in compatible FANUC i-Series controls. It is a plug-in DIMM-style module for the applicable CNC motherboard, not a complete control board or general-purpose memory card.

FANUC documentation lists A20B-3900-0072 as an 8M FROM module in the Series 16i/18i/21i/20i-A hardware family. The module is also described in the aftermarket as Program Memory C for selected 16i, 18i and 21i configurations.

A20B-3900-0072 Product Information

FROM Module Function

A FROM module contains the system software required by the CNC control. It is different from an SRAM module, which is associated with machine data such as parameters, programs and offsets. Replacing the FROM module does not automatically transfer the original machine configuration or software options.

Software and System Compatibility

Confirm the complete A20B-3900-0072 marking, PCB revision, CNC series, motherboard model, control generation, machining or turning software, system edition and option configuration. A blank module or one programmed for another machine may require the correct system software to be loaded before the control can operate.

Testing and Replacement Notes

REACO CNC checks the module label, PCB condition, memory devices, solder joints, edge connector and system recognition as applicable. Back up CNC parameters, PMC data, programs, offsets and other machine data before opening the control. Installation and software restoration should be performed by qualified FANUC personnel using the correct backup and boot procedure.

Related resources: FANUC CNC and robot parts and FANUC CNC board repair services.