A20B-3900-0013 Fanuc PCB Board A20B39000013 A2OB-39OO-OOI3

FANUC A20B-3900-0013

6MB Servo-Memory / FROM Module for 16i / 18i / 21i Controls

Main Description

The FANUC A20B-3900-0013 is commonly described as a servo-memory module with 6MB data capacity, and other replacement listings identify it as a 6MB FROM memory module for 16i, 18i, and 21i controls.

Taken together, those descriptions position the board as a memory component used in the control architecture of older i-Series systems rather than as a general-purpose PCB.

For a product page, the strongest positioning is to describe A20B-3900-0013 as a 6MB internal memory module for FANUC i-Series controls.

That keeps the description technically honest while still reflecting the two common market descriptions: servo-memory module and FROM memory module.

In service work, this type of board is usually needed when the control still has value and the correct memory board is the most direct way to preserve the original architecture.

Parameter Table

Technical Buying Perspective

A20B-3900-0013 is the kind of part that buyers usually search by exact model number first, then by memory capacity and control family. That is because older FANUC memory boards often have a narrow application window even when their physical format appears familiar. For service teams, the key benefit is continuity: if the installed 16i / 18i / 21i control is still worth maintaining, a correct 6MB memory-board replacement is often a more practical solution than changing the control platform itself. This is an engineering inference grounded in the board’s recurring use as a 6MB replacement memory part for those control families.

FAQ

Q1: What is A20B-3900-0013 used for?
It is used as a 6MB internal memory module in older FANUC controls. Listings describe it both as a servo-memory module and as a 6MB FROM module for 16i, 18i, and 21i systems, which places it in the controller memory path rather than in the operator interface or power section.

Q2: Why do sellers describe it in two different ways?
Because different replacement channels emphasize different aspects of the same board. One description focuses on servo-memory module, while another highlights 6MB FROM memory and its use in 16i / 18i / 21i controls.

The safest practical interpretation is that it is a 6MB internal memory board tied to those FANUC control families.

Q3: Which controls is this board commonly associated with?
It is commonly associated with 16i, 18i, and 21i controls. That fit matters because it gives the board a defined service context and helps buyers distinguish it from memory boards meant for other FANUC generations or robotics applications.

Q4: What should technicians check before replacing A20B-3900-0013?
They should confirm the exact installed part number, verify the target control family, and inspect the board connector and receiving socket.

Because the part is sold as an internal memory module, it should be treated as a configuration-sensitive board rather than as a generic card. 

After installation, stable startup and normal control behavior should be verified. 

The replacement guidance here is engineering best practice supported by the board’s listed role as an internal 6MB memory module.

Q5: Is this mainly a repair-market part?
Yes. The way it appears in current listings is strongly oriented toward replacement, surplus, and service support, which makes it much more relevant to maintenance and restoration than to new machine design.

For long-life i-Series hardware, that is exactly the kind of board a service department keeps in stock.