Fanuc Circuit Board A20B-2901-0941 A2OB-29O1-O941 A20B29010941

FANUC A20B-2901-0941 | 4MB DRAM Module — Series 15-B (Main-C) / Series 18 CNC / SMD

4MB of Working Memory for the Series 15-B CNC

The A20B-2901-0941 is the 4MB DRAM module used in FANUC's Series 15-B CNC in its Main-C configuration and in certain Series 18 CNC variants. It supplies volatile working memory — the active RAM where the CNC processor runs the system software, processes axis interpolation, manages operator interface data, and handles all real-time CNC computation during operation.

FANUC's Series 15-B represented the high-performance end of the FANUC CNC range at its time — complex multi-axis systems, precision contouring, and demanding production applications. The Main-C configuration is a specific hardware variant within the 15-B family. Each hardware configuration specifies a defined memory capacity, and the A20B-2901-0941 at 4MB meets this specification.

The SMD format means the module plugs directly into a socket on the main CPU board, making physical installation and removal straightforward — the module connects through its socket contacts without cable or wiring. The DRAM content is volatile and resets on every power-on; the CNC loads its operating software from the FROM module into DRAM at startup. Replacing the DRAM module therefore does not require FROM data restoration or parameter reloading — it only requires confirming that the new module is correctly seated and that the CNC completes its startup sequence normally.

Key Specifications

DRAM vs SRAM vs FROM — Three Different Memory Roles

On a FANUC CNC board, three memory types coexist and serve different functions:

A DRAM failure does not cause loss of CNC parameters or programme data — those are in SRAM and FROM. It prevents the CNC from operating, because the processor has no working memory to run from.

FAQ

Q1: Does replacing the A20B-2901-0941 DRAM module require reloading CNC parameters?

No. DRAM is volatile — it loads fresh from the FROM module at every power-on and carries no persistent machine-specific data. Parameters, part programmes, and tool data are stored in the SRAM module and FROM. Replacing the DRAM module only requires confirming correct seating and verifying the CNC starts up normally.

Q2: What symptoms indicate the DRAM module has failed on a Series 15-B CNC?

A DRAM fault typically prevents the CNC from completing its startup sequence — the control either displays a memory error alarm during boot or fails to initialise at all. If the CNC boots partially but hangs at a specific stage of startup, a DRAM fault is consistent. Confirm by swapping with a known-good A20B-2901-0941 if available for comparison.

Q3: Is the A20B-2901-0941 compatible with Series 15-A CNC as well as 15-B?

The A20B-2901-0941 is confirmed for Series 15-B (Main-C) and certain Series 18 configurations. Series 15-A uses a different hardware architecture and different memory modules — the A20B-2901-0941 is not confirmed for 15-A. Confirm the CNC model from the control unit's hardware label before ordering.

Q4: What is the /02A revision suffix on A20B-2901-0941/02A?

The /02A identifies a hardware revision of the base A20B-2901-0941 — a component-level or layout update made during production while maintaining the same function and compatibility. The /02A revision serves the same Series 15-B Main-C position as the base module. Both are valid replacements.

Q5: Where is the A20B-2901-0941 sourced after discontinuation?

Through the FANUC Series 15-B and Series 18 memory module aftermarket — FANUC CNC parts dealers specialising in Series 15, repair services, and tested surplus suppliers. The Series 15-B platform has a large installed base that keeps aftermarket stock available. Confirm the 4MB capacity and Series 15-B (Main-C) compatibility before ordering.