A20B-3900-0070 Fanuc PCB Board A20B39000070 A2OB-39OO-OO7O

FANUC A20B-3900-0070

16MB FROM Program Memory Module for 16i / 18i / 21i Model A Controls

Main Description

The FANUC A20B-3900-0070 is a 16MB FROM program memory module used in 16i / 18i / 21i Model A control environments.

It is commonly described as a plug-in Program Memory C module that installs on the main system board, which makes it a dedicated internal memory component rather than a general-purpose PCB.

On a product page, this model is best positioned as a program memory replacement module for i-Series controls that still depend on their original main-board memory structure.

That gives the part a clear industrial role: it is used where the controller remains worth maintaining and the correct FROM module is needed to preserve the original board-level configuration instead of moving toward a larger hardware change.

Parameter Table

Engineering Notes

A20B-3900-0070 should not be treated like a generic memory card.

It belongs to the program-memory side of the control, so the exact module number matters more than visual similarity. In older Model A systems, that distinction is especially important because memory modules often sit alongside CPU, graphics, and servo-control hardware on the master board, and each board has a defined role in the original control structure.

For maintenance buyers, this makes the 0070 module particularly useful in board exchange programs, legacy control support, and repair inventory for machines that still rely on 16i / 18i / 21i Model A hardware.

When the machine remains productive, replacing the correct 16MB FROM module is often the most efficient way to restore the intended control-memory path.

FAQ

Q1: What is the A20B-3900-0070 used for in a FANUC control?
It is used as a 16MB FROM program memory module for 16i / 18i / 21i Model A controls.

In practical terms, this means it belongs to the stored program-memory side of the controller rather than to the servo amplifier, HMI, or general I/O section. 

That role makes it a specialized internal memory board rather than a broad “PCB replacement.”

Q2: Where is this module installed?
Listings describe it as a plug-in module on the main system board or i-Series motherboard.

That installation detail matters because it places the board inside the controller’s internal memory stack. 

For technicians, this means replacement work should include inspection of the receiving socket and surrounding main-board area, not just the module itself.

Q3: Why is exact part-number matching important for A20B-3900-0070?

Because the A20B-3900 family contains several memory modules with different capacities and roles.

The 0070 model is specifically identified as a 16MB FROM program memory module, and that exact role is part of its compatibility.

In industrial repair, choosing by family alone is not enough; the safest approach is to match the exact board number and memory type.

Q4: Is this mainly a repair-market product?
Yes. The current market around this model is centered on replacement, surplus, and service supply.

That makes it far more relevant to repair and long-life maintenance than to new system design. 

For factories still running older Model A controls, a correct memory-module replacement is often more practical than broader control modernization.

Q5: What should be checked before replacing this module?
Technicians should verify the installed part number, confirm that the machine actually uses the Model A memory configuration, and inspect the master-board connector area before fitting the replacement.

After installation, it is good practice to confirm stable startup and correct control behavior. 

Those final checks are practical engineering guidance based on the board’s program-memory role and internal mounting position.