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| Place of Origin | JAPAN |
| Brand Name | FANUC |
| Certification | CE ROHS |
| Model Number | A20B-1006-0472 |
Part Number: A20B-1006-0472
Manufacturer: FANUC Corporation (Japan)
Product Type: Alpha Power Supply Module Base Wiring Board (Power PCB)
Board Series: A20B-1006
The A20B-1006-0472 is the base wiring board — the power section PCB — fitted inside FANUC's A06B-6087-H137 PSM-37 Alpha Power Supply Module. The PSM-37 is a key component in FANUC's Alpha shared-bus drive architecture: it converts incoming three-phase 200–230V AC into the regulated 283–325V DC bus that feeds the servo amplifier modules (SVM) and spindle amplifier modules (SPM) connected to it.
The A20B-1006-0472 is where this power conversion physically takes place.
Within the 150mm-wide PSM-37 module, two boards are assembled: the A20B-1006-0472 power board and the A16B-2202-0424 control card. The control card manages the PSM-37's monitoring, regulation feedback, and alarm logic.
The A20B-1006-0472 is where the high-current switching happens — it carries the three IGBT transistor modules that rectify and regulate the incoming AC into the DC bus, the DC bus capacitors that filter the converted voltage, and the current and voltage sensing circuits that feed back to the control card.
The "Alpha Base" designation reflects its position in the module assembly — it is the base board of the PSM-37 stack.
The screw terminals on this board are the physical connection points for the incoming AC power lines and for the module's various monitoring and control signal connections.
Multiple input and output connections serve the full set of signals the PSM-37 exchanges with the machine's power cabinet and with the connected drive modules.
| Parameter | Value |
|---|---|
| Part Number | A20B-1006-0472 |
| Manufacturer | FANUC Corporation |
| Product Type | Alpha PSM Base Wiring Board |
| Board Series | A20B-1006 |
| Compatible Module | A06B-6087-H137 (PSM-37) |
| Associated Control Card | A16B-2202-0424 |
| Module Output | 43 kW |
| AC Input | 200–230V, 3-phase, 150A |
| DC Bus Output | 283–325V DC |
| IGBT Modules | 3 (within module) |
| Module Width | 150 mm |
| Cooling | External heatsink + internal and external fans |
| Terminals | Screw terminals |
| Compatible CNC | Series 16i, 18i, 21i |
| Origin | Japan |
| Status | Discontinued by Manufacturer |
FANUC's Alpha drive system uses a shared DC bus architecture. One PSM serves multiple drive modules simultaneously.
The PSM draws AC power from the machine's main supply, rectifies and regulates it to the DC bus voltage, and distributes that bus voltage to all connected SVM and SPM modules. Each drive module draws current from the bus when motoring and — in regenerative operation — returns current to the bus.
The PSM manages the bus voltage, protecting it from overvoltage when regenerated energy exceeds what other modules can absorb, and from undervoltage when total motoring demand exceeds the PSM's capacity.
The A20B-1006-0472's IGBT modules perform the AC-to-DC conversion at the core of this process.
Three IGBTs form the active rectifier stage. Unlike passive diode rectifiers, the IGBT-based active rectifier can control the input current waveform, achieving near-unity power factor and allowing the energy flow to be reversed — enabling regenerative braking energy from the motors to be returned to the AC supply rather than dissipated as heat in braking resistors.
This is the fundamental efficiency advantage of the PSM architecture over earlier drive systems.
The PSM-37 module's front panel carries a single-digit seven-segment LED display that shows alarm codes when a fault is detected. These alarm codes are the primary diagnostic tool for the PSM-37 and, by extension, for determining whether the A20B-1006-0472 is the fault source.
Power board-related alarms include overcurrent in the main power circuit (typically caused by an IGBT failure), abnormal DC bus voltage rise (suggesting a gate drive or IGBT commutation fault), and main capacitor charge failure.
Control board-related alarms typically involve communication faults, fan failures, or thermal sensor readings.
Reading the specific alarm code from the display and mapping it to the fault category is the correct first step before deciding which board requires replacement.
The 150mm module also has two cooling fans — one internal and one external — plus the external heatsink.
An AL-02 alarm (cooling fan stopped) indicates a fan failure, not a power board fault.
Fan replacement is the corrective action, and it is urgent: continued operation without adequate cooling causes IGBT junction temperatures to rise rapidly toward the failure threshold.
The "multiple inputs/outputs" description in the A20B-1006-0472's product designation reflects the comprehensive signal termination that the base wiring board provides. Beyond the main AC power input and DC bus output connections, the board terminates the monitoring signals for DC bus voltage, module temperature, fan status, and the interconnection signals that the PSM-37 exchanges with the connected SVM and SPM modules to coordinate bus management.
The screw terminal connection method on this board is standard practice for high-current power connections in industrial drive systems.
Screw terminals provide secure, vibration-resistant connections that can accommodate a range of wire sizes and that are accessible for maintenance inspection without special tools.
For the AC input terminals carrying 150A, correct torque on the terminal screws is critical — an undertorqued connection at this current level generates heat that accelerates insulation degradation and eventually produces a connection failure.
Q1: The PSM-37 shows alarm AL-07 (DC bus voltage abnormally high) persistently. The drive system load is normal and no motors are operating in heavy regeneration. Is the A20B-1006-0472 the likely fault?
AL-07 with normal load and no heavy regeneration points to a fault in the IGBT active rectifier stage — specifically, an IGBT that is not switching correctly, allowing the DC bus to rise unchecked. This is a power board fault on the A20B-1006-0472.
The active rectifier control loop can no longer regulate the bus voltage. The PSM-37 module exchange or repair is the appropriate action.
Do not attempt to reset and resume operation — an uncontrolled DC bus voltage rise can damage the connected SVM and SPM modules.
Q2: The PSM-37 module was working correctly and then failed suddenly after a brief power outage. What should be inspected on the A20B-1006-0472?
Sudden failure following a power event typically indicates a transient overvoltage that exceeded the IGBT or DC bus capacitor ratings.
Inspect the main fuses within the PSM-37 module first — these are the first line of protection and may have blown cleanly.
If the fuses are intact, the IGBTs or the surge suppression devices on the power board may have failed.
Fuse replacement alone is not sufficient if the underlying cause was component damage; the module requires professional evaluation before being returned to service.
Q3: The A20B-1006-0472 and A16B-2202-0424 boards are described as not available separately. Can the IGBT transistor modules on the power board be sourced and replaced individually?
Specialist Fanuc drive service providers do offer IGBT module replacement as a repair service for the PSM-37.
The specific IGBT module type used in the PSM-37 can be identified from the component markings on the board.
Individual transistor module sourcing is possible from industrial electronics distributors.
However, IGBT replacement requires careful gate drive circuit testing after the new module is installed, and the replacement module must be thermally bonded correctly to the heatsink.
This is a board-level repair that requires proper equipment and expertise.
Q4: The machine uses two SPM spindle modules and four SVM servo modules connected to a single PSM-37. Is the PSM-37 appropriately sized for this configuration?
Sizing a PSM requires calculating the total peak demand of all connected modules simultaneously. The PSM-37 provides 43kW continuous.
The connected drive modules' combined peak demand — which occurs during acceleration — must not exceed the PSM's capacity.
Check the nameplate ratings of each connected SPM and SVM module and sum their peak current draws.
If the combined peak demand approaches or exceeds 43kW, the PSM-37 is undersized for the configuration and should be replaced with a higher-rated PSM, or the machine's acceleration rates should be reduced to limit peak current draw.
Q5: The PSM-37 is from a machine that is being decommissioned. Is it worth salvaging the A20B-1006-0472 power board as a spare?
A decommissioned PSM-37 with known good service history is a valuable source of spare boards — provided the board's condition is assessed before trusting it in production. Inspect the IGBT modules for any signs of thermal stress or mechanical damage.
Measure the DC bus capacitors' capacitance and ESR if test equipment is available.
A board from a machine that was retired due to obsolescence rather than drive failure may be in excellent condition and suitable for many more years of service.
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