1 PC Used Fanuc A20B-3300-0291 Circuit Board In Good Condition A20B33000291 A2OB-33OO-O291

A20B-3300-0291 | FANUC 486DX CPU Module with 16MB Built-In DRAM — Series 15i / 16i / 18i / 21i / i-Series Model B

16MB DRAM — Integrated, Not Add-On

The A20B-3300-0291 distinguishes itself from other A20B-3300 CPU cards in one significant way: the 16MB of DRAM is built directly onto the CPU card itself. There is no separate memory expansion card to order, no additional module to install, no risk of a loose memory card connector causing intermittent faults. The full 16MB working memory is on the same PCB as the 486DX processor.

This integrated design simplifies spare part management. A single replacement card delivers both the CPU processing capability and the full DRAM memory capacity in one part number, one shipment, and one installation operation.

Key Specifications

486DX Architecture — The Processing Core

The Intel 486DX is the floating-point-equipped variant of the i486 processor. The "DX" suffix specifically indicates the integrated floating-point unit (FPU) — the hardware circuit that executes trigonometric, logarithmic, and floating-point arithmetic instructions directly in silicon, without software emulation.

In CNC processing, the FPU is essential. Circular and helical interpolation, coordinate transformation for tilted work planes, and speed-dependent feedrate calculations all involve floating-point mathematics. A processor with a hardware FPU executes these operations in a fraction of the time required by software-emulated equivalents, enabling the CNC to close the interpolation loop at the required rate regardless of programme complexity.

Application Scenarios — CNC and Robot

Series 16i Model B CNC: A Series 16i Model B machining centre's CPU module fails. The A20B-3300-0291 is the correct replacement — providing the 486DX processor and 16MB DRAM that the Model B hardware expects. Installation is direct with no additional memory card required.

Series 18i turning centre: A turning centre using a Series 18i Model B CNC develops boot failure. Diagnosis identifies the CPU module. The A20B-3300-0291 replacement restores the CNC with its full 16MB DRAM capacity already on-board.

Robot control application: A FANUC robot system using i-series control hardware in the Model B configuration uses the A20B-3300-0291 as its CPU card. The 16MB integrated DRAM supports the robot controller's programme and operating state requirements.

FAQ

Q1: How is the A20B-3300-0291 different from the A20B-3300-0070 (486DX2 card)?

Both use Intel 486-architecture processors, but there are two key differences. First, the A20B-3300-0070 uses a 486DX2 (66 MHz, double-clocked) while the A20B-3300-0291 uses a 486DX. Second, the A20B-3300-0291 includes 16MB of DRAM built-in, whereas the A20B-3300-0070 is a separate CPU card that works with a separate DRAM memory module. They also target different hardware generations: 0070 is for Model A; 0291 is for Model B. They are not interchangeable.

Q2: Is the 16MB DRAM on the A20B-3300-0291 sufficient for all Series 15i/16i/18i/21i applications?

The 16MB figure covers the full working memory allocation for the i-series Model B generation's CNC software, operating system, programme buffer, and PMC execution environment under normal operation. For applications with exceptionally large programme libraries or advanced options requiring additional data memory, consult the FANUC hardware configuration manual for the specific CNC model to confirm whether 16MB meets the application's requirements.

Q3: Will an A20B-3300-0291 replacement cause any difference in CNC performance compared to the original?

A replacement A20B-3300-0291 card of the same revision will perform identically to the original. If replacing a lower-revision card with a later revision, minor hardware updates within the same specification should be transparent to the CNC's operation. FANUC hardware revisions within the same part number maintain backward compatibility with the existing CNC software and parameter set.

Q4: What is the correct procedure if the CNC fails to start after fitting the A20B-3300-0291?

First, verify the card is correctly seated in its slot — insufficient insertion is a common cause of startup failure after board replacement. Check that any retention hardware (screws, clips) is engaged. Next, verify the CNC's FROM and SRAM memory modules are present and the SRAM battery is charged. If the CNC cannot find the system software (IPL alarm), the FROM module may need to be reloaded. Consult the FANUC maintenance manual for the CNC model for the specific post-replacement startup procedure.

Q5: Can the A20B-3300-0291 be used in a Series 21i-A (Model A) CNC?

No. The A20B-3300-0291 is for the i-series Model B generation. Fitting a Model B CPU card into a Model A motherboard is not supported — the CPU card slot interface may differ between hardware generations. Always confirm the CNC's exact hardware generation (Model A or Model B) from its system diagnostics before ordering a replacement CPU card.