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| Place of Origin | JAPAN |
| Brand Name | FANUC |
| Certification | CE ROHS |
| Model Number | A20B-3900-0040 |
The FANUC A20B-3900-0040 is a 12MB DRAM module used in FANUC i-Series control hardware.
It is commonly associated with 15i, 16i, 18i, and 21i systems and is described as a plug-in memory board that fits on the main system board rather than in the amplifier or operator-panel section.
On an industrial product page, the most useful way to position this model is as an exact DRAM memory replacement module for older FANUC controls that still depend on the original internal memory structure.
That phrasing is more accurate and more helpful than calling it a generic PCB, because buyers typically search for this part by model number, memory size, and control family.
| Parameter | Value |
|---|---|
| Part Number | A20B-3900-0040 |
| Brand | FANUC |
| Product Type | DRAM Module |
| Memory Capacity | 12MB |
| Module Style | Plug-in memory module |
| Commonly Listed Controls | 15i / 16i / 18i / 21i |
| Installation Context | Main system board |
| Typical Use | CNC memory replacement |
A board like A20B-3900-0040 is valuable because it preserves the original memory layout of the control. In service work, that matters more than broad “performance improvement” language.
When the CNC is still worth maintaining, replacing the correct DRAM module is often the cleanest way to restore the intended hardware structure without changing the wider control platform.
This practical positioning follows from the module being sold specifically as a 12MB DRAM plug-in board for i-Series controls.
Q1: What is the A20B-3900-0040 used for in a FANUC control?
It is used as a 12MB DRAM memory module in FANUC controls such as 15i, 16i, 18i, and 21i. In practical terms, that means it belongs to the controller’s internal working-memory section rather than to the servo amplifier, spindle drive, or operator interface.
Q2: Why is exact part-number matching important for this module?
Because memory modules in the same family can look similar while still having different capacities or intended control generations.
For A20B-3900-0040, the 12MB DRAM identity is a defining feature. In repair work, the safest approach is to match the full part number rather than assume compatibility from appearance or family number alone.
Q3: Where is this module installed?
It is described as a plug-in memory module on the main system board. That is important because it tells the technician the board belongs to the internal memory stack of the CNC, not to an external or field-wired section. In practice, that means the connector area and receiving socket should be checked as part of the replacement process.
Q4: Is this mainly a repair-market part?
Yes. The current market presentation around this model is centered on replacement and service supply rather than new-system design.
That makes it most relevant to maintenance departments, repair shops, and users supporting older but still productive FANUC controls.
Q5: What should be checked before replacing A20B-3900-0040?
A technician should confirm the exact installed module number, verify the control family, and make sure the observed fault actually points to the memory path.
It is also good practice to inspect the main-board socket and confirm that the surrounding control hardware does not show related faults before fitting the replacement.
The final service steps are practical engineering guidance supported by the board’s listed role as an internal DRAM module.
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