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| Place of Origin | JAPAN |
| Brand Name | FANUC |
| Certification | CE ROHS |
| Model Number | A20B-3900-0071 |
The FANUC A20B-3900-0071 is a 12MB FROM memory module used in Series 15i, 16i, 18i, and 21i Model A controls.
Seller descriptions identify it as a DIMM-style program memory module that plugs into the i-Series motherboard / main system board, which makes it a specific control-memory component rather than a general PCB.
On a product page, this model is best described as a program memory module for i-Series Model A controls.
That is a more precise and more useful description than simply calling it a circuit board, because the part is searched and purchased primarily by capacity, memory type, and control family.
In service work, it is valuable when the machine still depends on its original program-memory hardware and the correct 12MB FROM module is needed to preserve the intended control structure.
| Parameter | Value |
|---|---|
| Part Number | A20B-3900-0071 |
| Brand | FANUC |
| Product Type | FROM Memory Module |
| Memory Capacity | 12MB |
| Module Style | DIMM memory module |
| Commonly Listed Controls | 15i / 16i / 18i / 21i Model A |
| Installation Context | Main system board / i-Series motherboard |
| Typical Use | Program memory replacement |
A20B-3900-0071 is not an SRAM board and not a mixed memory card.
It is sold specifically as a 12MB FROM module, which is why it is better suited to applications involving stored program memory on Model A controls.
In repair terms, that means this board should be selected as a program-memory part and not as a general substitute for other A20B-3900 modules with similar physical appearance.
Q1: What is the A20B-3900-0071 used for?
It is used as a 12MB FROM program memory module in 15i, 16i, 18i, and 21i Model A controls. Its role is in the control’s program-memory section, which is why it is marketed and serviced as a memory module rather than as a generic PCB.
Q2: Where is this module installed?
Listings describe it as a DIMM module that plugs into the main system board or i-Series motherboard.
For a technician, that means the board belongs to the controller’s internal memory stack and should be serviced with the same care given to other master-board memory components.
Q3: Why is the 12MB FROM specification important?
Because the 12MB FROM value is part of the module’s exact functional identity.
Even within the same A20B-3900 family, different memory boards may use different technologies and capacities.
In a CNC control, program memory configuration is not something to approximate casually, so matching the exact module is the safer option.
Q4: Is this mainly a repair-market part?
Yes. The way A20B-3900-0071 is sold today is strongly oriented toward replacement, surplus, and service support, which makes it much more relevant to repair and long-life maintenance than to new system development.
That fits the typical use case for older Model A controls still running in production.
Q5: What should be checked before replacing this module?
The installed part number should be confirmed first, followed by the target control family and the receiving DIMM connector on the main board.
Because this is a program-memory module, it is also wise to confirm that the control’s issue really belongs to the FROM memory path before removal.
After installation, stable startup and correct control behavior should be verified before returning the machine to service.
The last checks are practical engineering guidance based on the module’s listed role and installation context.
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