Fanuc PCB Board A20B-2902-0670 Used In Good Condition A20B29020670 A2OB-29O2-O67O

FANUC A20B-2902-0670 | Beta i Power Supply Driver Board — For biSVSP Servo/Spindle Combo Drives, A06B-6134 Series, SVSP-40/40-15i and Multi-Axis Configurations

Overview

The FANUC A20B-2902-0670 is the power supply driver board inside the FANUC biSVSP series — FANUC's integrated combination module that places servo axis drive capability and spindle drive capability in a single compact unit.

The biSVSP concept addressed a real panel engineering problem: traditional CNC drive cabinets required separate servo amplifier modules (SVM) and a separate spindle amplifier module (SPM), consuming substantial panel width and requiring individual bus connections between them.

The biSVSP integrates both functions — servo axes and spindle — into one module, dramatically reducing the panel footprint and simplifying the wiring topology.

Inside a biSVSP module, three distinct printed circuit boards work together in a defined physical and electrical arrangement. The control board manages the digital control algorithms, CNC communication (FSSB or similar), and axis/spindle control logic.

The wiring board provides the connector interface points for external cables — motor power, encoder feedback, control signals. The power board — of which the A20B-2902-0670 is the driver section — handles the actual power conversion: receiving the three-phase AC input, generating the DC bus, switching the IGBT modules for servo and spindle outputs, and providing the regulated lower-voltage DC rails for the control and wiring boards.

The A20B-2902-0670 specifically is the driver section of this power board assembly — the portion that carries the gate drive circuits, the logic-level power supply circuits, and the interface between the power conversion hardware and the control signals from the control PCB.

It is not the full power board (which carries the IGBTs and rectifier); it is the driver PCB mounted on the power board that bridges the low-voltage digital control domain and the high-power switching domain.

Key Specifications

biSVSP Architecture — Three-Board Integration

The biSVSP module's three-board architecture is more tightly integrated than the two-board architecture of the earlier Alpha SVM and SPM modules.

In the Alpha SVM2 (A06B-6079), for example, replacing the top card (A20B-2001-0931) is a straightforward swap because the top and base cards are mechanically and electrically independent. 

In the biSVSP, the three boards share signal paths and power planes that interconnect through backplane connectors, and the physical layout of the A06B-6134 module is more compact — making individual board identification and replacement more complex.

This integration is the reason some specialist repair centres prefer to service the biSVSP as a complete unit, exchanging the entire A06B-6134 module rather than replacing individual boards.

When a biSVSP module is returned to a repair centre, the technician has access to the full assembly, can perform diagnostic measurements at all interfaces simultaneously on a test rig, and can replace whichever board or component has failed. 

The A20B-2902-0670 driver board within the power section is one of the identifiable replaceable sub-assemblies within this repair process.

Power Supply Driver Board — What It Controls

Within the biSVSP's power section, the A20B-2902-0670 driver PCB performs functions that are essential to both the servo and spindle output channels:

Gate drive signal generation: The IGBT modules in the biSVSP's servo and spindle output stages require gate drive signals — precise timed pulses at the correct voltage level — to switch on and off at the correct phase in the PWM cycle.

The gate drive circuits on the driver PCB translate the low-power PWM signals from the control board into the higher-voltage, higher-current pulses needed to reliably switch the IGBT gates at the speeds required for motor control (typically 2–8kHz carrier frequency).

Isolated power supply for gate drivers: Driving IGBT gates in a half-bridge or full-bridge configuration requires bootstrap or isolated power supplies — each IGBT gate drive circuit needs a local power supply referenced to its own emitter potential, which floats at different potentials during switching.

The driver PCB carries the isolated power supply circuits (typically small high-frequency transformers or charge pump circuits) that provide these floating gate drive supplies.

Interlock and protection signal routing: The driver PCB carries the charge relay control, DC bus pre-charge logic enable, overcurrent trip logic, and the enable/disable signals that allow the control board to safely sequence the power section during startup, normal operation, and fault conditions.

The biSVSP in CNC Machine Tool Applications

The biSVSP module's integration made it particularly attractive for CNC lathes and smaller machining centres where the combined drive real estate in the electrical cabinet is limited.

A typical two-axis CNC lathe (X and Z servo axes, plus a spindle) could be served by a single biSVSP module — one box, one AC input connection, one DC bus, one fan — versus the traditional arrangement of two SVM modules and one SPM that would occupy three times the panel width.

The A06B-6134 biSVSP series covers a range of servo/spindle current combinations, from the smallest SVSP-40/40-15i (where "40/40" describes two servo axes and "15i" the spindle rated current) through triple-servo/spindle combinations serving three servo axes and a spindle.

The A20B-2902-0670 driver board is common across this range of configurations — its gate drive and power supply circuits are fundamentally the same regardless of the specific current rating of the IGBT stage it drives.

FAQ

Q1: Should the A20B-2902-0670 be ordered separately, or is it better to exchange the complete A06B-6134 module?

For most maintenance scenarios, a complete module exchange (sending the failed A06B-6134 to a repair centre and receiving a tested replacement) is the lower-risk approach.

The biSVSP's tight board integration means that diagnosing which specific board has failed requires test rig access that most production maintenance teams don't have on-site.

If the A20B-2902-0670 has been positively identified as the faulty board by a specialist who has the test equipment — and if the remaining boards in the module are confirmed serviceable — ordering the driver board alone is the lower-cost path. 

Without this diagnostic certainty, fitting a replacement driver board into an assembly with an undetected fault on the control board or wiring board results in a second failed module.

Q2: What are the typical fault symptoms in a biSVSP module that suggest the power driver board (A20B-2902-0670) has failed?

Power driver board faults typically present as: failure of the module to energise the DC bus (the DC bus charge relay does not close, or the pre-charge circuit fails to ramp the bus voltage, suggesting the driver board's charge relay control circuit has failed); one or more servo or spindle output channels producing incorrect or no motor current despite correct control commands (suggesting a gate drive circuit failure for the affected IGBT legs); or overvoltage/overcurrent alarms that correlate with specific power switching events and do not respond to parameter adjustment.

Contrast this with control board faults (FSSB communication errors, encoder faults) and wiring board faults (connector-specific issues affecting signal integrity on specific cables).

Q3: Can the biSVSP module operate temporarily with only servo function if the spindle driver section fails, or vice versa?

No. Because all three output channels (servo axes and spindle) share the common power board, DC bus, and power driver PCB, a failure in any section of the power driver board typically disables the entire module.

The biSVSP is not designed for graceful degraded operation with partial board failure — its integration trades operational flexibility for compactness.

A fault on the driver PCB that disables the spindle output also prevents the servo axes from operating safely, because the protection and interlock logic is common across all channels on the driver board.

Q4: What are the most failure-prone components on the A20B-2902-0670 in long-service biSVSP modules?

In extended-service biSVSP modules (10+ years), the most commonly failed components on the driver board are: electrolytic capacitors on the auxiliary power supply circuits (age-related capacity loss, ESR increase, and eventual electrolyte venting); optocouplers in the isolation barriers between control signals and gate drive circuits (degrade through LED ageing in the optocoupler transmitter, increasing the time constant of the isolation barrier and causing gate drive timing distortions at higher switching frequencies); and small signal transistors and ICs in the charge relay control circuit, which can fail through thermal stress in modules mounted in poorly ventilated locations.

A full component replacement focusing on these areas, performed by a specialist, substantially restores the driver board's reliability.

Q5: What precautions are necessary when the A20B-2902-0670 board is inside a module that needs to be opened for inspection or repair?

The biSVSP module's DC bus capacitors retain dangerous voltages (potentially 300–600V DC depending on the supply voltage) for several minutes after AC power is removed.

Before opening the module for any inspection or board removal, confirm that the DC bus has fully discharged by observing the "charge" LED on the module face (it must be extinguished), and then measure the DC bus terminals with a meter rated for the voltage.

Personal protective equipment (insulated gloves appropriate for the voltage, eye protection) is required during this verification. ESD precautions are additionally required whenever the control electronics boards are exposed, as the driver board carries CMOS gate drive ICs that are sensitive to electrostatic discharge.