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| Place of Origin | JAPAN |
| Brand Name | FANUC |
| Certification | CE ROHS |
| Model Number | A20B-1006-0481 |
Part Number: A20B-1006-0481
Manufacturer: FANUC Corporation (Japan)
Product Type: Spindle Amplifier Power PCB (Base / Wiring Board)
Board Series: A20B-1006
Compatible Drive: A06B-6088-H222 (SPM-22 Alpha Spindle Amplifier Module)
The A20B-1006-0481 is the power section PCB — the base wiring board — inside FANUC's A06B-6088-H222 Alpha spindle amplifier module, the SPM-22.
In the 6088 series Alpha spindle drive architecture, each module contains a layered assembly of boards serving distinct functions: the control card (A16B-2202-0432) handles the signal-level intelligence, the firing board (A20B-2902-0390) provides the gate drive signals, and the A20B-1006-0481 is the power stage board that handles the high-current transistor switching which actually drives the spindle motor.
The SPM-22 is a 22kW class spindle amplifier — the middle tier of the 6088 series, sitting between the SPM-15 and SPM-26 models. It drives FANUC's Alpha 22, Alpha 15, Alpha P22, and Alpha P30 spindle motors, using M-sensor or position coder feedback for speed and orientation control.
The module is 150mm wide, houses both internal and external cooling fans with an external heatsink, and features the characteristic twin seven-segment LED display that shows the drive's operating status and alarm codes.
The A20B-1006-0481 carries the IGBT power transistors and their associated current sensing circuits that handle the full motor current — 95A rated output — at the DC bus voltage (283–325V).
At these current and voltage levels, the components on this board are under significant electrical and thermal stress during normal operation.
Component aging, particularly of the IGBT modules themselves and the electrolytic capacitors in the gate drive power supply section, determines the board's practical service life.
| Parameter | Value |
|---|---|
| Part Number | A20B-1006-0481 |
| Manufacturer | FANUC Corporation |
| Product Type | Spindle Amplifier Power PCB |
| Board Series | A20B-1006 |
| Compatible Drive | A06B-6088-H222 (SPM-22) |
| DC Bus Input | 283–325V |
| Rated Output Current | 95A |
| Compatible Motors | Alpha 22, Alpha 15, Alpha P22, Alpha P30 |
| Cooling | External heatsink + internal & external fans (150mm module) |
| Status Display | Twin 7-segment LED (on complete drive module) |
| Origin | Japan |
| Condition Available | Via complete drive module exchange or repair |
The A06B-6088-H222 belongs to FANUC's Alpha series drive system — the architecture that pairs a shared PSM (Power Supply Module) with separate servo amplifier modules (SVM) and spindle amplifier modules (SPM) on a common DC bus.
The PSM generates the DC bus from the incoming three-phase AC supply. The SPM-22 draws from this bus and converts it to the variable-frequency three-phase output that drives the spindle motor.
Within the SPM-22, the A20B-1006-0481 is where this power conversion happens.
The IGBT transistors on this board switch the DC bus voltage to generate the three-phase sinusoidal output. Each IGBT must switch from fully off to fully on and back thousands of times per second, with the precise timing and duty cycle controlled by the gate signals from the firing board above.
The resulting switched output, after filtering in the motor's inductance, produces the smooth sinusoidal current that creates the rotating magnetic field in the spindle motor.
The 95A output rating means each phase of the SPM-22 output can deliver 95 amps continuously.
This represents a significant amount of electrical power — at the DC bus voltage, it corresponds to the full 22kW spindle rating.
The transistors and their heat management must handle this current continuously during heavy cutting operations.
The most practically important knowledge for maintaining 6088 series spindle drives is the distinction between control board faults and power board faults. This distinction determines which board to replace.
Control board faults (A16B-2202-0432) produce alarms related to communication, parameter handling, feedback processing, and the software-level functions of the drive. The drive may produce alarm codes that indicate communication errors with the CNC, parameter mismatches, or feedback signal abnormalities.
The power stage may be electrically intact.
Power board faults (A20B-1006-0481) produce alarms related to overcurrent, IGBT faults, transistor failures, and current sensing errors.
The motor may receive incorrect or absent output current. In severe cases — transistor short circuit, for example — the drive may trip its input protection and stop completely.
Identifying which board is at fault before ordering a replacement avoids the cost and delay of replacing an undamaged board.
Reading the specific alarm code from the drive's LED display and mapping it to the appropriate fault category is the starting point for this diagnosis.
FANUC's policy and the practice of most specialist service providers is not to sell the A20B-1006-0481 as a standalone board.
The board is available as part of a complete SPM-22 drive module exchange or as a component in drive-level repair service.
This approach makes functional sense: verifying that the board is correctly functional requires testing it under real motor load in a complete drive unit, not on a bench without a connected motor.
When a spindle fault is identified as originating in the power board, the practical service options are: complete SPM-22 exchange (fastest), drive-level repair where the specific failed component on the power board is identified and replaced, or IGBT module replacement where the fault is specifically in the IGBT device.
All of these options require the complete drive unit to be available.
Q1: The SPM-22 shows an IGBT alarm code and the spindle cannot run. The control card has been tested and is confirmed good. Is the A20B-1006-0481 the fault location?
An IGBT alarm with a confirmed good control card points to the power board. IGBT alarms can indicate a failed transistor (short or open circuit), a failed IGBT gate drive circuit that prevents correct switching, or a current sensing fault.
All of these are located on the A20B-1006-0481. In cases where the IGBT itself has shorted, there may also be damage to the DC bus fuse or upstream circuit protection.
Check the drive's protection fuses before proceeding with board-level work.
Q2: After the SPM-22 trips on an overcurrent alarm, it resets and runs correctly for a while before tripping again. The pattern repeats. What does this indicate about the power board?
Intermittent overcurrent alarms that reset and recur suggest a thermal or marginal electrical fault rather than a complete component failure.
The most common cause is an IGBT that is performing marginally — it passes the drive's power-on checks and runs correctly at lower loads, but fails under the thermal stress of full-load operation.
The drive trips, the component cools, and it runs again until thermal stress recurs. An IGBT that behaves this way will eventually fail permanently.
Arrange exchange or repair of the complete SPM-22 before production is stopped by a hard failure.
Q3: The SPM-22's external cooling fan has stopped. How urgent is replacement, and could the power board be damaged by running without it?
The external fan is critical for the power board's thermal management. FANUC 6088 series spindle modules generate substantial heat in the IGBT transistors during operation. Without adequate airflow over the external heatsink, transistor junction temperatures will exceed safe limits.
Running without the external fan during heavy cutting will cause IGBT thermal failure within minutes to hours depending on load. Replace the fan immediately.
Do not continue production until the fan is replaced — the IGBT modules are far more expensive than the fan.
Q4: The A20B-1006-0481 and A20B-1006-0487 are both listed for the A06B-6088-H222. Are they interchangeable?
Both the -0481 and -0487 are power boards that have been used in the A06B-6088-H222 SPM-22 module.
They are variants within the same application, potentially representing hardware revisions or production changes within the same drive model.
Whether they are interchangeable in a specific drive unit depends on which board was originally installed and whether the revision difference affects the drive's thermal or electrical interface.
Confirm with the service specialist supplying the drive module rather than assuming interchangeability.
Q5: The SPM-22 drive is being decommissioned from one machine. Can the A20B-1006-0481 power board be salvaged and used as a spare for another SPM-22?
Salvaging the power board from a decommissioned drive is possible, but its condition must be assessed before trusting it in another production machine.
Inspect the IGBT modules for any signs of damage — discolouration, cracking, or physical evidence of overload. Measure the IGBT forward voltage drop and leakage to verify they are within specification. Assess the electrolytic capacitors' condition.
A board from a decommissioned machine may have substantial operational hours and component aging that make it unsuitable for continued service without refurbishment.
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