FANUC A20B-3900-0053

256KB SRAM Module for 16i / 18i / 20i / 21i Controls

Product Overview

The FANUC A20B-3900-0053 is a 256KB SRAM module for 16i / 18i / 20i / 21i control applications.

It is commonly sold as a DIMM-style memory module that installs directly on the i-Series master board, which places it firmly in the control-memory section rather than in the drive or interface hardware.

Its value in service work comes from precision rather than size.

This is the kind of board a repair department keeps because older FANUC controls often require the exact SRAM module originally specified for the system. 

Even a small-capacity SRAM board can be critical when the machine depends on retained controller data and a correct board-level memory match.

Parameter Table

Professional Use Context

A20B-3900-0053 is best described as a retained-memory support board.

One seller note also states that data will be lost during the replacement process and needs to be restored, which is a meaningful service detail for this module.

On a real machine, that means the board should be treated not only as hardware, but also as part of a controlled backup-and-recovery process.

That is why the 0053 module makes sense in repair inventory, exchange service, and legacy CNC support.

It is especially relevant in shops that still handle i-Series memory-board faults and need exact SRAM replacements rather than approximate substitutes from the same family.

FAQ

Q1: What does A20B-3900-0053 do in a FANUC system?
It serves as a 256KB SRAM memory module in the internal control-memory architecture of 16i / 18i / 20i / 21i systems.

In practical terms, it belongs to the retained-memory path of the control and is handled as an internal memory component rather than as a user-facing or drive-side board.

Q2: Why is this small-capacity SRAM board still important?
Because memory boards are chosen by role and exact configuration, not just by headline capacity.

A relatively small SRAM module can still be essential if the control expects that exact board in its original memory layout. In industrial maintenance, the right 256KB SRAM board is more useful than a larger but incompatible module.

Q3: Does replacement involve data considerations?
Yes. A service listing for this part specifically notes that data will be lost during replacement and needs to be restored.

That makes the board more than a simple hardware swap. Technicians should think in terms of backup discipline, restore planning, and verification after installation.

Q4: Where is this module installed?
It is described as a DIMM memory module that fits directly onto the i-Series master board.

For technicians, that means the receiving socket, contact condition, and board seating are all part of a proper replacement procedure.

Q5: Why is exact matching important for A20B-3900-0053?
Because SRAM modules in the same family may differ in capacity and intended control generation.

The 0053 board is specifically tied to the 256KB SRAM role for i-Series controls, and that exact identity is what makes it the correct replacement.