FANUCA20B-2902-0351CNC Memory Module, 768 K Battery-Backed SRAM Daughter Board, F16B / Series 16-18

Product Description

What this part is

A Fanuc A20B-2902-0351 memory module. It is a daughter board, catalogued at 768 K of SRAM, that mounts onto an F16B-generation Fanuc CNC main board — the board family behind the Series 16 and Series 18 controls. Its function is memory capacity: part-program storage, parameters, macros and tool data.

Correcting the source data

Earlier copy described this as a module for PLCs and HMI systems providing control and motion capabilities. It does neither. It has no processor, drives nothing, and controls no motion — it is memory that a CNC main board reads and writes. If a control is short of part-program memory or has lost its stored programs, this is the relevant module; if an axis will not move, it is not.

Decoding the order code

A20B — Fanuc drawing prefix for a smaller printed circuit board, typically a daughter or option card. The larger main boards carry the A16B prefix, and A86L is reserved for bought-in components rather than Fanuc’s own PCBs.2902 — drawing group. The 29xx groups belong to the later Fanuc CNC generations rather than the early Series 6 boards.0351 — the specific module04B — drawing revision level, marked on the board. Record the revision on the module you remove.

What SRAM memory means for this machine

Fanuc SRAM memory is volatile and battery-backed. That has two practical consequences a buyer should plan for. First, capacity is a hardware fact, not a setting: if the machine needs more program memory than the fitted module provides, the module has to change. Second, the contents live only as long as the backup battery holds — so before touching memory hardware on a working control, punch out your part programs, parameters, pitch-error compensation and PMC data. Recovering a machine whose parameters were never backed up is a far longer job than the board swap that lost them.

Published specifications

Function: CNC memory module, part-program and parameter storageMemory type: SRAM, battery-backedCapacity: 768 K, as catalogued for this drawing numberPlatform: Fanuc F16B main board generation, Series 16 and Series 18 family controlsFanuc drawing number: A20B-2902-0351Revision seen on this drawing: 04BForm factor: daughter board, mounts on the host CNC main boardCountry of manufacture: Japan

Installation and setup notes

Back up programs, all parameter files and PMC data before you start, and have a known-good backup battery to hand. Power the control down fully and discharge before opening the cabinet; Fanuc boards are static-sensitive and the racks hold charge. Note which connector position and orientation the outgoing module occupies on the main board — these daughter boards seat on board-to-board connectors and are easy to mis-seat by one row. Expect memory-related alarms and a memory-clear sequence at first power-up after fitting new memory hardware, then reload parameters before you reload programs; loading programs into a control with wrong parameters is how machines get crashed.

Quantity and configuration

One memory module. The CNC main board, card rack, mounting standoffs and screws, backup battery, cables and the parameter or program data are not included — memory arrives blank.

Interchange guidance

Order against the full drawing number. The neighbouring A20B-2902 modules are different capacities and different functions and are not drop-in substitutes: fitting a different capacity changes what the control reports and may not be accepted by the machine’s option configuration. A20B-2902-0531 is a separate board entirely despite the similar digits, so read the number carefully. Also written A20B29020351, A20B 2902 0351, A20B-2902-0351/04B and A20B-2902-0351#04B.