FANUC Servo Control Board A20B-2001-0931 A2OB-2OO1-O931 A20B20010931

A20B-2001-0931 | FANUC Alpha Series SVM2 Two-Axis Servo Drive Control Board — Type-A Interface / SVM2-12/12 to SVM2-40/40

SVM2 Module Architecture — Two PCBs, One Housing

The FANUC Alpha series SVM2 is a two-axis servo amplifier — one module driving two servo motors simultaneously. Inside the module, two PCBs work in combination:

The wiring board (A16B-2202-xxxx / A16B-2203-xxxx): the passive connection layer. It carries the DC bus input, motor output power terminals, encoder feedback connectors, and the Type-A interface cable connection.

The control board — A20B-2001-0931: the active processing layer. This top card receives axis commands from the CNC via the Type-A interface, runs current control loops for both axes, processes encoder feedback, executes protection and diagnostic logic, and generates gate drive signals for the IGBT power switches.

When the drive behaves abnormally — persistent alarms, axis communication failure, incorrect current regulation — the A20B-2001-0931 is the board-level replacement target for the control section.

Key Specifications

Type-A Interface — CNC-to-Drive Communication

Type-A is the analogue-digital servo bus that FANUC used in the Alpha series drive generation. A dedicated cable runs from the CNC's servo interface board to the SVM2's Type-A input on the A20B-2001-0931. Through this cable, the CNC sends position and velocity commands each servo update cycle, and the drive returns position feedback and status data.

This is a generation earlier than the fibre-optic FSSB interface used in later FANUC systems. Machines with Type-A drives use dedicated wiring from the CNC to each servo module, making the interface reliability of the A20B-2001-0931's Type-A circuitry critical to the machine's axis communication.

Application Scenarios

Two-axis servo drive repair: A two-axis servo module develops a control alarm that clears temporarily on reset but returns immediately when the drive is enabled. The wiring board and power section test correctly. Replacing the A20B-2001-0931 control board resolves the persistent alarm and restores both axis functions.

Spare parts planning: A maintenance team supports a machine shop with multiple FANUC Alpha series SVM2 drives across different current ratings. Stocking one A20B-2001-0931 covers the control board replacement need across all SVM2-12/12, SVM2-20/20, and SVM2-40/40 units.

FAQ

Q1: Is A20B-2001-0931 the same control board regardless of SVM2 current rating?

Yes. The control board function and circuit design are the same across SVM2 variants from 12/12 through 40/40 and beyond. Current rating differences are handled by the power stage and wiring board. A single A20B-2001-0931 replaces the control board in any of these SVM2 configurations.

Q2: Can A20B-2001-0931 be installed in an SVM3 (three-axis) module?

No. SVM2 and SVM3 modules use different control boards matched to their specific axis count and module architecture. SVM3 three-axis control boards have different part numbers. The A20B-2001-0931 is specific to two-axis SVM2 modules only.

Q3: How is the control board replaced without disturbing the power section?

The A20B-2001-0931 top card sits above the wiring board, connected via board-to-board connectors and the Type-A cable. Replacing the control board requires disconnecting only the Type-A interface cable and the board-to-board connection — no high-current motor wiring or DC bus connections are disturbed. The wiring board and power components remain in place during the control board swap.

Q4: What alarm codes typically indicate A20B-2001-0931 failure?

Alarms related to servo bus communication (Type-A link errors), axis-specific current regulation faults that appear on both axes simultaneously (since one control board manages both axes), and drive alarms that persist regardless of motor or encoder cable condition all point toward the control board. Single-axis alarms under normal load typically suggest the motor, encoder, or power device for that specific axis rather than the common control board.

Q5: Do servo parameters need to be reloaded after fitting a replacement A20B-2001-0931?

Servo parameters are held in the CNC's parameter memory, not in the servo drive control board. Replacing the A20B-2001-0931 does not affect any stored CNC parameters. After fitting the replacement and restoring Type-A communication, the CNC applies the existing servo parameters automatically. Verify axis readiness and perform a low-speed test move before returning the machine to production.