FANUC PCB Board A20B-3300-0392 A20B33000392 A2OB-33OO-O392

FANUC A20B-3300-0392 | 4-Axis i-B Series Servo Module — FSSB Plug-In PCB for Series 16i / 18i / 21i Model B

Part Number: A20B-3300-0392

Manufacturer: FANUC Ltd. (Japan)

Product Type: 4-Axis i-B Series Servo Module — Plug-In PCB

Four-Axis Servo Control on One Card

The A20B-3300-0392 is FANUC's 4-axis FSSB servo module for the i-B Series CNC. It plugs into the 16i, 18i, or 21i Model B main board and extends the CNC's servo control capability to four axes via a single FSSB fibre-optic channel. Each axis the module manages receives position and velocity commands from the CNC, processes encoder feedback via the FSSB bus, and returns real-time position data for closed-loop servo control.

The "i-B" designation identifies this module as a Model B generation component — the second hardware generation of the FANUC i Series platform, which succeeded the original Model A boards. The Model B architecture uses a higher-density plug-in format that integrates servo control, FSSB interface, and signal processing in a compact card that mounts alongside the CPU processor, graphics controller, and memory modules (SRAM, DRAM, FROM) on the main board assembly.

In a typical 16i/18i/21i Model B control, the A20B-3300-0392 is one of several plug-in modules that together make up the complete CNC control unit. Its FSSB channel connects to the servo amplifier chain via fibre-optic cable at the board's optical connector.

A20B-3300 Series Context

The A20B-3300 series encompasses FANUC's plug-in modules for i Series CNC and robot controllers. Within this family:

• 4-axis variants (including A20B-3300-0392) serve machines with up to 4 controlled axes on a single FSSB chain
• 6-axis variants serve 5- or 6-axis configurations
• 8-axis variants provide the highest axis count on a single module

All A20B-3300-series modules share the same plug-in form factor for the Model B main board. They are not interchangeable between axis count configurations.

Key Specifications

FAQ

Q1: The CNC shows servo alarm 360 or 361 on axes managed by this module. What is the first diagnostic step?

Alarms 360/361 are FSSB communication faults. Re-seat the A20B-3300-0392 in its slot on the main board first — a marginal connector contact is the most common cause. Then inspect the FSSB fibre-optic cable from the module's optical connector to the first servo amplifier in the chain. A damaged or contaminated fibre end face breaks communication on all axes in that chain simultaneously.

Q2: Does the A20B-3300-0392 replace earlier Model A servo modules in the same CNC?

No. Model A and Model B CNC systems use physically different main board architectures. Model A boards use a different plug-in format. The A20B-3300-0392 is specific to Model B (i-B series) main boards. Confirm the CNC is a Model B variant before ordering.

Q3: The board was removed for inspection. Does it need to be re-initialised after reinstallation?

The A20B-3300-0392 stores no CNC parameters. All axis parameters reside in the CNC's FROM/SRAM. After reinstallation, the CNC reads its parameters normally at power-up. No re-initialisation step is required.

Q4: A 6-axis machine uses the A20B-3300-0392 (4-axis module). How are the additional axes controlled?

On a 6-axis machine, a second servo module — either another 4-axis board or a 2-axis module — is fitted to handle the remaining axes. Two modules can be installed on the same Model B main board in their respective slots. Each has its own FSSB fibre-optic chain connecting to the servo amplifiers for its assigned axes.

Q5: Where is a replacement A20B-3300-0392 sourced?

The FANUC aftermarket holds exchange stock for A20B-3300-series modules. Specialist FANUC CNC repair companies offer tested exchange units. For a model B control requiring immediate repair, companies with full-system test rigs can verify the module's function on a 16i/18i/21i platform before shipment.