FANUCA20B-2902-01962 MB DRAM Working-Memory Module for Series 16 / 18 / 21 CNC, Model B and C — CPU Board Daughter Card

Product Description

What this part is

This is a 2 MB DRAM memory module for Fanuc Series 16, 18 and 21 CNC controls of the model B and C generations. It is a small daughter card that plugs onto the main CPU board of the control, and it supplies the working memory the main processor uses while it is running — scratch space for the data it pulls out of the FROM and SRAM modules during machining. On a control fitted for a small configuration, 2 MB was the mid-capacity option of the period.

Decoding the order code

A20B – Fanuc printed circuit board / module drawing prefix2902 – the module block used for Series 16/18/21 CPU-board daughter cards. Its neighbours are the memory and display modules for the same platform: 0210 is a 1 MB CMOS SRAM module, 0270 and 0278 are 14-inch colour CRT control modules, 0271 a 9-inch monochrome graphic engine, 0272 an 8.4/9.5-inch LCD control module.0196 – 2 MB DRAM module/02A – drawing revision, marked on the board. Fanuc revision suffixes on memory modules are usually component-level changes rather than functional ones, but they are worth recording when you order a matching spare.
Also written A20B29020196, A20B 2902 0196 and A20B-2902-0196-02A.

DRAM, not SRAM — and why the difference decides your fault:
Some listings for this part number call it a 2 MB SRAM module. That is worth correcting, because on a Fanuc control DRAM and SRAM do entirely different jobs and buying the wrong one wastes a shutdown.

DRAM is volatile working memory. It is not battery-backed, it holds nothing when the control is off, and it stores no user data. It is the processor’s scratchpad.

SRAM on these controls is battery-backed and holds the things you care about losing: machine parameters, PMC ladder, tool offsets, macro variables and part programs. FROM is flash and holds the system software.

The practical consequence: replacing this DRAM module does not erase your parameters and does not restore a control that has lost them. Conversely, if your fault is corrupted parameters or a lost program after a dead battery, this is not the module that will fix it. DRAM faults show up as system alarms, random resets or failures partway through boot — not as missing data.

Published specifications

Function: DRAM working-memory daughter moduleCapacity: 2 MBConstruction: surface-mount modulePlatform: Fanuc Series 16, 18 and 21, model B and model C generationsMounting: plugs onto the main CPU board of the control unitBoard marking: A20B-2902-0196/02A

What is not included

Memory module only, one piece. Not supplied: the main CPU board it plugs into, the control unit rack or card cage, the FROM or SRAM modules, the memory backup battery, any option board, the boot software or system parameters, and any cabling. This module is a component of a CPU board assembly, not a standalone unit — it does nothing outside a Series 16/18/21 control.

Installation and setup notes

Power the control down and observe static precautions; this is a bare surface-mount module with an exposed edge connector and it is unforgiving of handling. Note the orientation and the exact position on the CPU board before you remove the original, because the 2902 block contains several physically similar modules that do very different jobs. Fanuc boards of this generation are firmware-and-configuration sensitive: matching the base number is the first requirement, and if your control was commissioned with a particular revision it is worth matching that too rather than assuming. After fitting, expect the control to boot normally — a DRAM change does not require re-entering parameters.

Interchange guidance

Search forms include A20B-2902-0196, A20B29020196, A20B-2902-0196/02A and A20B 2902 0196. Other modules in the A20B-2902 block — 0210, 0213, 0270, 0271, 0272, 0278 — are different modules on the same platform, not equivalents: different capacities, different memory technologies, or display controllers rather than memory. Do not substitute across that block. Fanuc CNC boards of this generation are strongly dependent on system generation and firmware, and a one-digit difference in the part number frequently is not interchangeable. Fanuc has long discontinued this generation; surplus, reman and specialist board repair are the supply channels.