1 PC Used Fanuc A20B-2900-0620 In Good Condition A20B29000620 A2OB-29OO-O62O

A20B-2900-0620 | FANUC C-Series AC Servo Control Board — Daughter PCB / Digital Servo Drive / C-Series Amplifier / Multi-Axis CNC

C-Series AC Servo — FANUC's Pre-Alpha Digital Drive Generation

The FANUC C-Series represents the generation of FANUC AC servo drives that preceded the Alpha series. Introduced in the 1980s alongside FANUC's expanding CNC product range, the C-series brought digital servo control to a broad installed base of FANUC CNC machine tools. These drives powered a generation of machining centres, turning centres, and multi-axis machines that remain in production service today.

In the C-series drive architecture, the servo control function is distributed across multiple PCBs. The A20B-2900-0620 is one of these PCBs — a daughter board that adds supplemental digital servo drive circuitry to the main servo amplifier unit. Its role is to extend the drive's capability within the amplifier assembly, providing additional servo control and signal processing on top of the host unit's existing electronics.

Key Product Information

PWM Digital Servo Control in C-Series

The C-series drives use PWM (Pulse Width Modulation) as their current control method — switching the output transistors at high frequency with a duty cycle that determines the effective current delivered to the servo motor. This digital approach provided:

• Precise, repeatable current regulation across the motor's speed range
• Cleaner torque output than analogue predecessors
• Compatibility with digital position feedback from encoders

The A20B-2900-0620's circuitry supports this PWM architecture within the C-series amplifier unit.

Application Scenarios

C-series servo amplifier repair: A FANUC C-series servo amplifier develops a fault traced to the daughter board. The A20B-2900-0620 is identified from its part number label inside the drive. Replacement restores the servo amplifier's digital control function.

Multi-axis C-series system maintenance: A multi-axis CNC machine with Series 16 Model A control and C-series servo amplifiers requires a replacement board for its extended-axis servo control. The A20B-2900-0620 is fitted to restore the additional axis channels.

FAQ

Q1: How does the A20B-2900-0620 differ from the main servo board in the C-series amplifier?

The main servo board provides the core servo amplifier functions: DC bus interface, IGBT gate drive, and primary current control. The A20B-2900-0620 is a supplemental daughter board — it adds specific digital servo drive circuitry on top of the main board's capability. Both must be present and functional for the amplifier to operate correctly.

Q2: What CNC systems were used with C-series AC servo drives that use this board?

The related A20B-2900-0370 module is confirmed for "large Fanuc Series 16 Model A controls requiring more than 4 axes." The C-series drives were used with FANUC CNC systems of the Series 16-A and related Model A generation, which were deployed on larger machining centres and turning centres in the era when these drives were current.

Q3: What is the safe discharge procedure before accessing the C-series servo amplifier?

C-series servo amplifiers contain DC bus capacitors that retain dangerous voltage after mains power is removed. The discharge time depends on the amplifier's capacitor bank size. Wait for any charge indicator to extinguish and verify with a calibrated DC voltmeter before opening the amplifier housing to access the A20B-2900-0620.

Q4: Does A20B-2900-0620 store servo parameters?

No. Servo parameters (motor ID, gains, encoder type) are stored in the CNC's main parameter memory. The A20B-2900-0620 daughter board is a hardware logic board — it does not store any machine-specific data. Replacing this board does not affect CNC parameter settings.