Fanuc A20B-8100-0661 System Motherboard A20B81000661 A2OB-81OO-O661

A20B-8100-0661 | FANUC Series 18i-B Main CPU PCB — LCD-Mounted / 18i-MB / 18i-TB / Yellow Backplane / Master Board

The 18i-B Motherboard — Foundation of the Control System

The A20B-8100-0661 is the master PCB — the motherboard — of the FANUC Series 18i Model B CNC control system. Every other PCB in the 18i-B unit plugs into or connects through this board:

• The CPU card (A20B-3300-03xx series) provides processing power
• The video card drives the LCD display
• The servo control card communicates with FSSB-connected drives
• FROM and SRAM memory modules store software and data

The A20B-8100-0661 provides the backplane bus, the connector matrix, and the physical mounting surface for this entire stack. It defines the system's physical architecture — the specific connectors, slot arrangement, and bus interface that make the 18i-B a 18i-B rather than any other FANUC CNC generation.

Key Specifications

18i-MB and 18i-TB — Same Board, Different Machines

The A20B-8100-0661 is the common main board for two distinct machine types:

18i-MB (Machining Centre): A FANUC Series 18i CNC configured for vertical and horizontal machining centres. The MB designation activates machining centre-specific functions — canned drilling cycles, rigid tapping, tool length compensation, and tool radius compensation.

18i-TB (Turning Centre): The same 18i-B hardware configured for CNC lathes and turning centres. TB-specific functions include constant surface speed, thread cutting, and turning-specific canned cycles.

The hardware A20B-8100-0661 is identical in both. The system software image in the FROM modules determines whether the 18i-B operates as an M-type or T-type CNC. When the main board is replaced, the FROM content defines which machine type the system resumes as.

Application Scenarios

18i-MB machining centre motherboard failure: A machining centre CNC fails completely — display blank, all axes inhibited, no response. Power supply confirms correct output voltage. Diagnosis isolates the A20B-8100-0661 main board as the fault. After board replacement and system restore from backup, the machining centre returns to production.

18i-TB turning centre refurbishment: An older 18i-TB turning centre undergoes a complete CNC overhaul. The A20B-8100-0661 is replaced alongside the CPU card and memory modules as part of a board-level renewal, resetting all critical electronic components simultaneously.

FAQ

Q1: What CPU card is required with the A20B-8100-0661?

The A20B-8100-0661 supports the A20B-3300-03xx series CPU processor cards. The specific CPU card version depends on the CNC model revision and configuration. Confirm the exact CPU card part number from the system's existing configuration before ordering.

Q2: What data backup is essential before replacing the A20B-8100-0661?

Back up all SRAM contents before removing the main board: CNC parameters, all stored part programmes, tool offset data, work offset data, and PMC ladder programme and data. The FROM modules contain the CNC system software and should be left installed during main board replacement — they are separate from the A20B-8100-0661 and do not need special backup if they remain undamaged. Perform the backup via the CNC's SRAM backup function to a memory card or RS-232C-connected PC.

Q3: Does the A20B-8100-0661 carry any CNC software or is software stored elsewhere?

The A20B-8100-0661 motherboard does not store CNC software. System software resides in the FROM modules (flash memory modules), which are separate plug-in items that fit onto the main board. CNC parameters and programmes reside in SRAM modules. The A20B-8100-0661 itself is passive — it provides the bus and connectors, but no stored data of its own. Replacing the main board does not erase software, provided the FROM and SRAM modules remain intact.

Q4: Is the A20B-8100-0661 compatible with Series 16i-B or 21i-B systems?

No. The A20B-8100-0661 is specific to the 18i-B generation. The A20B-8100 series main boards cover different CNC models — different hardware in the same physical form class but with different bus connector arrangements and option card configurations. The 16i-B and 21i-B use their own main board part numbers. Do not substitute main boards between CNC model families.

Q5: Can the A20B-8100-0661 be repaired rather than replaced?

For a production-critical machine, direct board replacement is typically faster. For less urgent situations where a replacement board is unavailable, repair by a qualified FANUC service technician who can component-test and reflow the board is a viable alternative. Any repaired board should be fully tested on an 18i-B test rig before installation in a production machine.