PCB Board A20B-8100-0665 A20B81000665 A2OB-81OO-O665

A20B-8100-0665 | FANUC Series 21i-B Main CPU Board — Ethernet / PMC-SB7 / 21i-MB and 21i-TB / Yellow Backplane Motherboard

Series 21i-B — FANUC's i-Series Compact CNC Platform

The FANUC Series 21i-B is a member of the FANUC i-series CNC family — the generation that introduced FSSB digital servo communication, enhanced processing performance, and integrated Ethernet to compact CNC platforms. Within the i-series:

21i-MB: The machining centre variant of the Series 21i-B — serving vertical and horizontal machining centres with multi-axis interpolation, rigid tapping, and full machining centre functionality.

21i-TB: The turning centre variant — serving CNC lathes and turning centres with G-code turning cycle support, thread cutting, and lathe-specific functions.

The A20B-8100-0665 is the main CPU board common to both variants — the motherboard on which the CNC's primary processing, Ethernet communication, and PMC-SB7 sequence control are integrated.

Key Specifications

PMC-SB7 — Advanced Sequence Programme Capability

PMC-SB7 is the highest-capability PMC (Programmable Machine Controller) variant available in the Series 21i-B CNC system. The PMC is the CNC's integrated PLC — executing the machine tool's sequence logic in parallel with the CNC's axis motion:

Ladder programme capacity: PMC-SB7 provides expanded ladder diagram capacity — accommodating the full sequence logic of complex machine tools with multiple axes, automatic tool changers, pallet changers, and sophisticated safety interlocking.

High-speed scanning: The PMC-SB7 executes the ladder programme at a fast scan rate — ensuring machine tool I/O responses are fast enough for demanding real-time machine control requirements.

I/O capacity: The PMC-SB7 specification supports the maximum I/O point count available in the Series 21i-B platform — serving complex machines with extensive sensor and actuator I/O.

Application Scenarios

Series 21i-B CNC system fault — main CPU board: A FANUC 21i-MB machining centre develops system-level CNC faults — the CNC fails to complete power-on initialisation or displays CPU-level alarms. After verifying the CPU processor card and memory modules, the A20B-8100-0665 motherboard is identified as the fault. Replacement with full parameter and programme restore returns the machine to production.

Ethernet function fault on 21i-B: A Series 21i-TB turning centre loses Ethernet connectivity — DNC programme transfer and remote monitoring are lost. The A20B-8100-0665 is identified as the board incorporating the Ethernet interface. Replacement restores network connectivity.

FAQ

Q1: What is the difference between the A20B-8100-0665 and the A20B-8100-0661 or similar nearby part numbers?

The A20B-8100 series covers main CPU boards for multiple FANUC i-series CNC platforms. A20B-8100-0661 is the 18i-B main CPU board. A20B-8100-0665 is specific to the 21i-B. Despite close part numbers, these boards are CNC-platform-specific — the 21i-B board cannot be substituted for the 18i-B board or vice versa. Confirm the installed CNC model from the control unit's identification label before ordering.

Q2: After replacing A20B-8100-0665, must all CNC data be reloaded?

Yes — replacement of the main CPU board requires a complete reload of all CNC data: part programmes, axis parameters, servo parameters, PMC ladder programme, tool offset data, and all system configuration. The board itself contains no persistent user data — all data resides in the SMD memory modules (SRAM, FROM) mounted on the board. Before replacement, ensure a complete and verified backup of all CNC data is available.

Q3: Can the CPU processor (A20B-3300-031x) be transferred from the old to the new A20B-8100-0665?

In some cases the CPU processor card can be transferred if it is undamaged — this avoids re-registering the processor. However, if the CPU processor is suspected of contributing to the fault, replacing it along with the motherboard eliminates that uncertainty. Confirm from the applicable FANUC Series 21i-B maintenance manual whether the processor should be swapped or replaced fresh.

Q4: What alarms on the 21i-B CNC specifically indicate an A20B-8100-0665 fault?

Motherboard-level faults in the Series 21i-B typically manifest as: failure to complete power-on self-test with error codes displayed on the CNC's alarm screen, "System Alarm" or "Hardware Alarm" codes that cannot be attributed to any peripheral card, repeated "RAM parity" or "ROM error" alarms despite good memory modules, or complete loss of display/MDI function. These must be distinguished from memory module faults (which produce specific module-related error codes) and CPU processor faults before condemning the motherboard.

Q5: Does the A20B-8100-0665 support both the 21i-MB and 21i-TB configurations?

Yes — the A20B-8100-0665 is the motherboard for the 21i-B generation across both the machining centre (21i-MB) and turning centre (21i-TB) variants, as well as other 21i-B configurations. The machine type (MB or TB) is determined by CNC software and parameters loaded into the memory modules — the A20B-8100-0665 hardware itself is common to both.