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| Place of Origin | JAPAN |
| Brand Name | FANUC |
| Certification | CE ROHS |
| Model Number | A20B-1006-0483 |
Part Number: A20B-1006-0483
Manufacturer: FANUC Corporation (Japan)
Product Type: Control PCB
Board Series: A20B-1006
Application: FANUC Alpha series servo drive system
The A20B-1006-0483 is a control printed circuit board from FANUC's A20B-1006 series. The A20B-1006 family covers control and interface boards used within FANUC's Alpha series servo drive system — principally the internal control PCBs for the Power Supply Module (PSM) and related drive system components that form the backbone of FANUC's Alpha amplifier architecture.
These boards handle the control electronics for the drive system's power management, DC bus regulation, safety interlocks, and CNC communication functions.
The FANUC Alpha amplifier system was FANUC's principal drive platform for its generation of CNC machine tools.
In this architecture, the PSM converts the three-phase AC mains supply to a regulated DC bus that feeds the servo amplifier modules (SVM) and spindle amplifier modules (SPM).
The control board within the PSM — belonging to the A20B-1006 family — manages all of the PSM's intelligence: precharge sequencing, DC bus voltage regulation, regenerative energy management, fault detection, and communication with the CNC controller.
The A20B-1006-0483 represents one specific variant in this control board family, configured for the drive rating and feature set of its designated PSM model.
When a PSM develops a control fault — failing to maintain the DC bus, reporting incorrect status, or failing to communicate with the CNC — replacing the control board is the targeted maintenance action that addresses the fault without requiring replacement of the complete power module.
| Parameter | Value |
|---|---|
| Part Number | A20B-1006-0483 |
| Manufacturer | FANUC Corporation |
| Product Type | Control PCB |
| Board Series | A20B-1006 |
| Application | FANUC Alpha series servo drive system (PSM/drive control) |
| Drive Family | FANUC Alpha servo amplifier system |
| Origin | Japan |
| Operating Temperature | 0 – 55°C (as installed in drive unit) |
| Storage Temperature | −20 – 55°C |
| Humidity | 75% RH max (non-condensing) |
| Condition Available | New (surplus) / Refurbished / Repaired |
The FANUC Alpha amplifier system uses a shared DC bus topology. All the servo and spindle amplifier modules in one cabinet draw their motor drive power from a common DC voltage rail. The PSM creates and maintains this rail. It rectifies the incoming three-phase AC, filters the result, and regulates the DC bus voltage within acceptable limits throughout the machine's operating cycle.
The PSM control board is where all the intelligence for this process resides.
At power-on, the control board runs the precharge sequence: it gradually charges the DC bus capacitors to limit the inrush current that would otherwise flow if the full voltage were applied instantly to discharged capacitors.
Once precharge is complete, the control board commands the main contactor to close, connecting the fully charged bus to the SVM and SPM modules.
During operation, the control board monitors the DC bus voltage continuously.
When the servo motors decelerate, their regenerative energy flows back onto the DC bus.
The control board manages this regenerated energy — either returning it to the AC supply through an active regeneration circuit or routing it to a discharge resistor.
This management keeps the DC bus voltage from rising to damaging levels during deceleration.
When the A20B-1006-0483 control board develops a fault, the PSM cannot fulfil its role as the system's power source.
The symptoms depend on which circuit on the board has failed.
A failed precharge circuit prevents the DC bus from reaching operating voltage. The CNC receives a bus not ready status.
All drives remain inoperable — no motion is possible on any axis because none of the servo modules can operate without the DC bus.
A failed DC bus voltage measurement circuit produces incorrect voltage readings.
The control board either fails to detect a genuine bus fault or falsely reports an overvoltage or undervoltage condition.
The CNC alarms on bus faults that don't correspond to the actual bus state.
A failed CNC communication interface produces communication errors between the PSM and the controller.
The CNC reports that the PSM status is unknown or that the PSM has not responded.
FANUC's A20B-1006 series spans control boards for PSM units of different current ratings and hardware generations.
The PSM-15, PSM-26, PSM-30, PSM-37, PSM-45, and PSM-55 models — covering a wide range of drive system power capacities — each have their corresponding control board variant within this series. The -0483 variant is one specific board within this family, matched to its designated drive rating and hardware revision.
A replacement board must exactly match the installed board's part number.
Installing a control board from a different PSM rating can produce incorrect operation even if the board physically fits, because the control parameters and protection thresholds are matched to the specific hardware of each PSM model.
Q1: The machine shows a DC bus alarm at every power-on attempt. The AC input voltage is confirmed correct and the DC bus capacitors are not damaged. Could this be the A20B-1006-0483 control board?
Yes. A persistent DC bus alarm with confirmed good capacitors and correct AC input points to the control board's precharge circuit or DC bus measurement circuit.
The precharge circuit may not be completing correctly, preventing the bus from reaching operating voltage.
Alternatively, the voltage measurement circuit may be reading incorrectly, triggering a false alarm.
Inspect the control board for any visible damage and proceed to replacement if the board passes visual inspection but the fault persists.
Q2: The PSM powers on normally but the CNC shows repeated PSM communication errors during machining. The DC bus voltage appears stable. What should be checked?
PSM communication errors with a stable DC bus and normal operation point to the control board's CNC interface circuit rather than the power control circuits.
Check the communication cable between the PSM and the CNC controller for any damage or intermittent contact first.
If the cable is confirmed good, the control board's interface circuit has likely degraded. Replacing the control board is the appropriate next step.
Q3: After heavy regenerative braking during a rapid axis deceleration, the PSM tripped on overvoltage. The overvoltage alarm cleared after a power cycle and the machine seems to be working. Should the control board be inspected?
A single overvoltage trip from heavy regenerative braking is not necessarily a control board fault — it can indicate that the regenerative braking load exceeded the PSM's rated capacity.
However, if overvoltage trips become recurring, the control board's regenerative energy management circuit should be evaluated.
Recurrent trips can also degrade the bus capacitors over time.
Verify the machine's deceleration parameters and the drive sizing against the actual load profile before concluding the board is faulty.
Q4: The PSM control board is being replaced. Are there parameters stored on the board that need to be transferred?
PSM control boards in the Alpha series typically do not store user-adjustable parameters — the board's function is defined by its hardware design rather than software configuration. However, confirm this for the specific PSM model by checking the maintenance documentation.
After replacement, no software transfer is required for most configurations, but a full system test should confirm correct precharge, DC bus regulation, and regeneration behavior.
Q5: How is the correct A20B-1006-0483 variant confirmed against other A20B-1006 boards?
Read the part number from the label on the installed board. The A20B-1006 series includes boards for different PSM models and hardware revisions — the full part number including the -0483 suffix is the definitive identifier.
Do not substitute a similar-looking board from another PSM model without confirmed compatibility.
Physical dimensions and connector positions may appear identical between PSM variants while the electronic function differs.
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