The FANUC A20B-3900-0132 is a 4M SDRAM module used as CNC system working memory. It installs in the dedicated DIMM socket on a compatible CPU card and provides volatile memory for CNC software execution and real-time processing while the control is powered.

FANUC documentation identifies A20B-3900-0132 as the 4M memory option for the A20B-3300-0170 CPU card. It is commonly described as a 4MB DRAM module, but it must not be confused with SRAM backup memory or a FROM system-software module.

A20B-3900-0132 Product Information

CNC System Working Memory

A20B-3900-0132 provides temporary high-speed working memory required while the CNC is operating. Unlike SRAM, it is not the battery-backed area for machine data, and unlike FROM, it does not permanently store system software. A failed or poorly seated module may cause boot failure, RAM or parity alarms, resets or unstable operation.

Compatibility and Capacity Checks

Match the complete A20B-3900-0132 number, module revision, 4M capacity, CPU card and DIMM socket. A20B-3900-0130 and A20B-3900-0131 have different capacities. A20B-3900-0042 is also documented as a 4M memory module but for a different CPU-card arrangement, so equal capacity does not prove interchangeability.

Testing and Installation Notes

REACO CNC checks the label, contacts, memory recognition, reported capacity, CNC boot and stable operation on an applicable test system. Back up parameters, programs, offsets and PMC data before control hardware service. Isolate power, release the DIMM retainers carefully and use ESD protection during replacement.

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