FANUC A20B-3900-0141

8MB FROM / 1MB SRAM Module for FANUC CNC Memory Support

Main Description

The FANUC A20B-3900-0141 is best positioned as a combined FROM and SRAM memory module used in the internal memory structure of FANUC controls.

Listings for this model consistently describe it as an 8MB FROM / 1MB SRAM module, and it is commonly associated with 16i / 18i / 21i controls as well as Power Mate i applications.

In practical maintenance work, a board like this is used when the control still has production value and the correct memory module is needed to preserve the original storage layout.

One listing notes that the module plugs into the backside of the CPU or onto the main system board, which makes it a very specific internal control-memory component rather than a general-purpose PCB.

Parameter Table

Applications

The A20B-3900-0141 is well suited to control-memory replacement, board-level CNC repair, and long-term support of installed FANUC controls that still rely on the original FROM/SRAM structure.

It is especially useful in service departments that maintain 16i / 18i / 21i controls or Power Mate i systems and need a like-for-like memory module rather than a broad hardware change.

It also fits repair-stock planning and controller restoration work where preserving the original memory arrangement is more important than adapting a loosely similar module. Because this board is sold as a specific 8MB/1MB combination, exact part-number matching is a more reliable service strategy than relying on the family name alone.

Why Exact Matching Matters

The A20B-3900 family includes multiple FROM/SRAM combinations, so the 8MB / 1MB profile is part of what defines A20B-3900-0141 as a specific replacement.

On older FANUC controls, using the correct memory module helps preserve the original board-level storage layout and lowers the risk of compatibility problems during repair. 

This is exactly the kind of part that adds value in service inventory because it supports machine recovery without forcing a wider control conversion.

FAQ

Q1: What is A20B-3900-0141 used for in a FANUC system?
It is used as a combined 8MB FROM / 1MB SRAM memory module inside the controller’s internal memory structure.

In practical terms, that means it supports stored control software, parameters, and active system data rather than front-panel functions or drive control.

Q2: Why is exact part-number matching important for this module?
Because A20B-3900 memory boards are not interchangeable by appearance alone. The 8MB FROM / 1MB SRAM combination is part of the board’s identity, and listings tie this exact module to specific FANUC control families.

In maintenance work, using the correct part number is the safer way to preserve the intended memory layout.

Q3: Where is this module installed?
One seller description states that it plugs into the backside of the CPU or onto the main system board.

That installation detail is important because it shows the board belongs to the internal control-memory stack rather than to a removable operator panel or amplifier assembly.

Q4: Is this mainly a repair-market part?
Yes. Current listings around this model are centered on replacement and memory-board supply, which makes it much more relevant to repair, restoration, and service inventory than to new-machine design.

Q5: What should technicians verify before replacing it?
They should confirm the exact installed module number, inspect the board connector area, and verify that the fault truly belongs to the memory path rather than to the main PCB or a software-side issue.

Because the module stores critical control information, post-installation checks should include normal startup and confirmation that the control recognizes the restored memory correctly. This last point is an engineering inference supported by the module’s stated memory role.