FANUC A20B-3900-0130

12MB DRAM Module for FANUC i-Series CNC Controls

Product Overview

The FANUC A20B-3900-0130 is a 12MB DRAM module in the A20B-3900 family. Multiple listings identify it as a DRAM memory board for FANUC 16i / 18i / 21i controls, and some descriptions also place it in the broader i-Series DIMM memory category used on the master board.

From a product-page perspective, this model fits naturally into the memory-expansion and memory-replacement side of CNC service.

It is not a general PCB and not a storage-plus-SRAM module like some other A20B-3900 boards. 

Instead, it is a DRAM-specific board used where the control requires the exact installed memory type and capacity to maintain proper operation.

Parameter Table

Applications

The A20B-3900-0130 is best suited to memory replacement in FANUC i-Series controls, especially where the machine uses the original DRAM configuration on the master board and a direct module replacement is the most practical solution.

It is a strong fit for controller repair, service inventory, and board-level restoration in 16i / 18i / 21i environments.

It also works well in workshops that maintain older i-Series hardware and need predictable, exact memory replacement rather than trial-and-error substitution.

Because the board is identified specifically as a 12MB DRAM module, the part is most useful when the service objective is to keep the original control platform in operation without changing the rest of the CNC memory architecture.

FAQ

Q1: What is A20B-3900-0130 used for?
It is used as a 12MB DRAM module in FANUC i-Series CNC controls. In practice, that means it belongs to the controller’s working-memory structure rather than to the display, power, or drive section.

Q2: Which controls is it commonly associated with?
Listings consistently associate it with 16i / 18i / 21i controls, and some sellers identify it specifically as an i-Series DIMM memory module for those platforms.

Q3: Why is it important that this is a DRAM module and not a FROM/SRAM module?
Because the module’s role in the control is different. DRAM boards belong to the volatile working-memory side of the system, while FROM/SRAM boards combine other storage functions. In service terms, that means A20B-3900-0130 should be matched as a DRAM memory part, not simply as any A20B-3900 board.

This explanation is an engineering inference based on the board being consistently described as a DRAM module.

Q4: Is this board mainly relevant to repair work?
Yes. The market around this model is centered on spare parts, replacement boards, and service supply, which makes it much more relevant to maintenance and restoration than to new machine design.

Q5: What should technicians verify before replacing A20B-3900-0130?
They should verify the exact installed part number, confirm the control family, and inspect the board seating and connector condition on the master board.

Because this is a memory module, it is also sensible to make sure the fault actually belongs to the memory path and not to the CPU board or a separate control issue. 

The diagnostic emphasis is an engineering best-practice inference based on the module’s listed role.