Fanuc Cpl Servo Card A20B-3300-0240 A20B33000240 A2OB-33OO-O24O

FANUC A20B-3300-0240 | 8-Axis i-B Series FSSB Servo Control Module — Series 16i / 18i / 21i / 0i CNC

Part Number: A20B-3300-0240

Manufacturer: FANUC Corporation (Japan)

Product Type: FSSB Servo Control Module — 8-Axis i-B Series Plug-In PCB

Axis Capacity: Up to 8 axes

Interface: FSSB (Fiber-optic Serial Servo Bus)

Eight Axes, One Plug-In Board

The A20B-3300-0240 is the 8-axis FSSB servo control module for FANUC's i-B Series CNC — the plug-in PCB that handles servo axis control for up to eight controlled axes from a single board mounted on the i-B Series main CPU. It uses FSSB (Fiber-optic Serial Servo Bus) to communicate with servo amplifiers in real time, transmitting velocity and position commands to the drives and receiving encoder feedback every control cycle.

The A20B-3300 series covers the plug-in servo modules for i-B Series CNC controllers (16i-B, 18i-B, 21i-B). Each board manages servo axis communication via one or more FSSB fibre-optic channels, with the number of axes and FSSB channels varying by module type. The A20B-3300-0240 supports up to 8 axes — the highest axis count in the standard single-board range for this CNC generation.

Within the A20B-3300 family, neighbouring part numbers address different axis count configurations:

The correct module for a specific CNC depends on the configured axis count and whether HRV (High Response Vector) servo control is required. Confirm the installed board's part number from its own label before ordering a replacement.

FSSB and the i-B Architecture

FSSB replaced the parallel PWM wiring of earlier FANUC drive generations with a single fibre-optic cable chain connecting the CNC to its servo amplifiers. Each FSSB channel from the A20B-3300-0240 connects to a chain of servo amplifiers, with each amplifier identified by its position in the chain. The fibre-optic connection provides noise immunity in the high-electromagnetic-interference environment inside a CNC machine cabinet.

The module plugs into the i-B Series main CPU board alongside the CPU processor module, memory DIMM modules (FROM and SRAM), and the graphics display module. Together these plug-in boards constitute the complete CNC controller. The A20B-3300-0240 holds no CNC parameters — all axis configuration and servo parameters reside in the SRAM module and the CNC's battery-backed memory.

Key Specifications

FAQ

Q1: FSSB alarms appear on multiple axes simultaneously after this module was reseated. What should be checked?

Multi-axis FSSB alarms after module handling point first to the module's connector seating on the main CPU board — a marginal contact on any pin of the module's edge connector produces exactly this symptom. Remove the module completely, inspect the connector for bent or contaminated pins, reseat firmly, and retest. If alarms persist, inspect the FSSB fibre-optic cable connections at the module's optical ports for contamination or damage.

Q2: Can the A20B-3300-0240 (8-axis) work in a CNC that only uses 6 axes?

Yes. The module supports up to 8 axes but does not require all 8 to be assigned. In a CNC configured for 6 axes, the two unused FSSB axis positions simply remain unassigned in the CNC's axis parameter table. The module operates normally with fewer than its maximum axis count configured.

Q3: Does replacing this module require any parameter re-entry?

The A20B-3300-0240 holds no CNC parameters. All servo axis parameters reside in the CNC's SRAM and FROM memory. After installing a replacement module, the CNC reads its parameters normally at power-up. No parameter re-entry is needed for a like-for-like module swap, provided the original SRAM content is intact.

Q4: What is the difference between the standard A20B-3300-0240 and the HRV variant A20B-3300-0248?

The A20B-3300-0248 is the HRV (High Response Vector) variant, which supports a higher servo loop update rate for more responsive axis control — particularly relevant for high-speed machining applications. The 0240 is the standard variant. Both plug into the same i-B Series main CPU board. The correct variant is determined by the CNC's servo software configuration — HRV control requires the HRV module and matching servo software parameters.

Q5: Where is the A20B-3300-0240 sourced?

The FANUC CNC aftermarket holds exchange and surplus stock for A20B-3300 series servo modules. Both the 0240 and closely related variants are actively traded because of the large installed base of 16i/18i/21i machines still in production. Confirm the exact suffix (0240) from the installed module's label — do not accept an adjacent number without verifying axis count and HRV compatibility. Request a functional test on a compatible CNC test rig before accepting any exchange unit.