FANUC A20B-3900-0060

2MB SRAM Module for 16i / 18i / 21i and Power Mate i Controls

Product Overview

The FANUC A20B-3900-0060 is a 2MB SRAM module in the A20B-3900 series. It is commonly associated with 16i, 18i, 21i, and in some listings Power Mate i, where it is described as a small modular board that plugs into the main master PCB inside the control.

This kind of board is used where the machine depends on its original SRAM memory structure and the most practical repair path is a direct memory-board replacement. In service environments, the value of A20B-3900-0060 is not just its capacity. Its real value is that it preserves the original memory configuration of the control and avoids introducing a different module profile into an established CNC platform.

Parameter Table

Why This Module Matters

For a repair buyer, the significance of A20B-3900-0060 is that it is an SRAM-specific board rather than a mixed FROM/SRAM module. That distinction matters in older FANUC systems, where one board may store retained data and another board may handle other memory functions. A 2MB SRAM module therefore needs to be matched as a memory-type part, not merely as a board from the right family.

FAQ

Q1: What is the A20B-3900-0060 used for?
It is used as a 2MB SRAM module in FANUC CNC controls, typically within 16i, 18i, 21i, and sometimes Power Mate i systems.

Its role is to support the internal memory structure of the control, which is why it is handled as a dedicated memory module rather than a general replacement PCB.

Q2: Is this board the same as a FROM module?
No. Listings describe A20B-3900-0060 specifically as an SRAM module, not a FROM module.

That difference is important because even boards in the same A20B-3900 family can serve different memory roles inside the controller. 

In service work, the board should be selected by exact type and capacity, not only by family number.

Q3: Where is this module installed?
Descriptions place it as a plug-in module on the main master PCB, alongside other major control boards and memory cards.

For technicians, that means replacement work should include checking the socket condition, connector contact quality, and general cleanliness of the board area rather than focusing on the module alone.

Q4: Why is exact capacity matching important for this model?
Because a 2MB SRAM module is not interchangeable with a 1MB or higher-capacity SRAM board simply because the outline looks similar.

The control’s intended memory layout depends on the exact installed module. 

In industrial maintenance, that means the 2MB SRAM specification is part of the board identity and should be matched directly during ordering and repair.

Q5: What is good practice before replacing A20B-3900-0060?
Technicians should verify the installed part number, confirm the target control family, and inspect whether the fault really belongs to the SRAM module path rather than to the master board or software side.

After installation, the control should be checked for stable startup and normal memory-related behavior.

While the sources focus on the board’s role and fit, the diagnostic workflow here reflects standard engineering practice for control-memory replacement.