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| Place of Origin | JAPAN |
| Brand Name | FANUC |
| Certification | CE ROHS |
| Model Number | A20B-2000-0220 |
Part Number: A20B-2000-0220
Manufacturer: FANUC Corporation (Japan)
Product Type: Serial Spindle Drive Control PCB (Sub Power Board)
Board Series: A20B-2000
Drive Series: A06B-6064 Series (Serial AC Spindle Servo Units)
Application: Serial AC spindle drive control for CNC machine tools
The A20B-2000-0220 is the serial spindle sub control board — the spindle drive PCB — fitted inside FANUC's A06B-6064 series serial AC spindle servo units. The 6064 series was FANUC's serial-command spindle drive generation: a significant technical step from the earlier 6044 and 6052 analog spindle units and the 6055 digital units.
Where the analog drives received a variable voltage spindle speed command from the CNC and the digital drives used a PWM interface, the 6064 series drives communicate with the CNC controller through a serial link — a bidirectional digital communication channel that carries speed commands from the CNC to the drive and status, speed feedback, and fault data from the drive back to the CNC.
This serial interface approach brought several practical advantages to the 6064-series machines. The CNC can monitor spindle speed in real time.
The drive can report detailed fault codes rather than simple alarm relay contacts.
The wiring between the CNC and the drive is reduced to a small serial cable rather than the multi-conductor analog or PWM command cables of earlier generations.
And spindle-related functions — orientation, rigid tapping synchronisation, spindle-servo mode — integrate more tightly because the serial communication path carries all the necessary data at high speed.
The A20B-2000-0220 is the board that implements all of this within the drive unit. It handles the serial interface decoding, the spindle speed control algorithm, the PWM switching signals for the drive's transistors, and the feedback processing from the spindle motor's position sensor.
It covers the 6S through 26S spindle motor range — a span of spindle motor sizes from the smaller machining centre spindles to the larger turning centre main spindles.
| Parameter | Value |
|---|---|
| Part Number | A20B-2000-0220 |
| Manufacturer | FANUC Corporation |
| Product Type | Serial Spindle Drive PCB (Sub Control Board) |
| Board Series | A20B-2000 |
| Drive Series | A06B-6064 (Serial AC Spindle Servo Units) |
| Motor Coverage | 6S – 26S (serial AC spindle series) |
| Command Interface | Serial (digital CNC-to-drive link) |
| Function | Speed control, serial interface, transistor gate drive |
| Origin | Japan |
| Operating Temperature | 0 – 55°C |
| Storage Temperature | −20 – 60°C |
| Status | Discontinued by Manufacturer |
The A06B-6064 series spindle drives appeared on a wide range of FANUC-controlled machine tools from the mid-1990s onward. They were matched to the CNC controllers of that era — Series 0-C, Series 15, Series 16, and Series 18 — all of which supported the serial spindle interface.
The 6064 units are yellow-cased drives with a compact rectangular profile. They contain a power section with transistor modules for the spindle motor output and a control section with the A20B-2000-0220 board as the central control PCB.
The serial communication link between the CNC and the 6064 drive uses FANUC's proprietary spindle serial protocol.
The CNC transmits speed commands and control words; the drive responds with its current speed, status word, and any alarm codes.
This bidirectional exchange runs on a continuous cycle, and the CNC uses the speed feedback to verify that the spindle reached the commanded speed — forming a soft closed loop at the system level even though the spindle speed itself is regulated by the drive's internal control loop.
Rigid tapping is one of the key functions that the 6064 serial spindle enables cleanly. In rigid tapping, the CNC synchronises the Z-axis feed with the spindle rotation to thread-cut without a floating collet chuck. The CNC needs to know the exact spindle position at all times.
The serial spindle interface in the 6064 system carries spindle position data (from the spindle's position coder) back to the CNC on every communication cycle.
The A20B-2000-0220 processes the position coder feedback and formats it for transmission on the serial link.
If the A20B-2000-0220 develops a fault in the position coder interface section, rigid tapping becomes unreliable.
Thread pitch errors, tapping alarms, or spindle orientation failures often trace back to a degraded position coder signal path on the spindle drive board.
The A06B-6064 series spindle drives contain two main boards: the power section (which carries the transistor modules and their gate drive circuitry) and the control section (the A20B-2000-0220, which handles everything above the power transistor level).
Fault isolation begins with the alarm code on the drive's LED display — power-section alarms (overcurrent, IPM fault, phase loss) point to the power board, while control-section alarms (communication errors, position coder faults, parameter alarms) point to the A20B-2000-0220.
The drive's LED display is the first diagnostic tool. A "–" (dash) or "E1" code at startup indicates a serial communication fault between the CNC and the drive — usually the serial cable or the board's serial interface circuit.
Alarm codes in the 01–09 range typically indicate power section faults. Codes above 30 generally indicate control section or position coder faults.
This code-to-section mapping guides the replacement decision.
Q1: The 6064 spindle drive shows a "–" or "E1" on its LED display at startup. The serial cable between the CNC and the drive is confirmed good. Is the A20B-2000-0220 the fault?
A serial communication failure with a confirmed-good cable points to the serial interface circuit on the A20B-2000-0220.
First check the CNC's spindle serial port — if the CNC is generating the serial signal but the drive does not respond, the drive's serial receiver on the board is likely faulty.
Also verify the serial communication parameter settings on the CNC match the drive's requirements.
If settings are confirmed correct and the cable is good, the board's serial interface section has failed and replacement is required.
Q2: The spindle drive runs the motor correctly in normal cutting but rigid tapping produces thread pitch errors. The Z-axis servo is confirmed accurate. Is the spindle drive board the cause?
Rigid tapping pitch errors with a confirmed accurate Z axis are usually caused by inaccurate spindle position feedback reaching the CNC. The position coder signal path — from the spindle encoder through the A20B-2000-0220 to the serial link back to the CNC — is the suspect chain.
First verify the physical condition of the position coder cable and its connectors on the drive and encoder. If cables are good, check the position coder feedback signal quality diagnostics on the CNC's servo diagnostic screen.
Signal quality degradation or intermittent dropout identifies a board-level fault.
Q3: An overcurrent alarm (typically alarm 12 in the 6064 series alarm list) appears consistently under spindle load. The motor winding insulation has been tested and is good. Is the A20B-2000-0220 the fault?
Overcurrent alarms under load with good motor insulation can originate from either the power transistor section or from a current sensing fault on the A20B-2000-0220. The drive board's current sensing circuits monitor the motor phase currents and shut the drive down if a set threshold is exceeded.
A drifted or failed current sensor reads a higher current than actually flows, causing nuisance overcurrent trips at normal load.
If transistors have been verified good, the current sensing section of the A20B-2000-0220 is the remaining suspect.
Q4: A replacement A20B-2000-0220 is being installed. Are there chip or jumper settings that must be transferred from the original board?
Yes — the 6064-series spindle control board carries spindle software in socketed ICs (EPROM/flash memory chips) that contain the motor-specific control software. These chips must be transferred from the original board to the replacement board before installation.
If the wrong software chips are installed, the spindle will either not run correctly or will generate immediate alarm codes on startup. Before any board swap, photograph and document the chip locations and markings on the original board.
Also transfer any voltage selection jumpers and other configuration links — document their positions before removal.
Q5: The 6064 series spindle unit and the A20B-2000-0220 board are both discontinued. What options exist for keeping this spindle drive generation operational?
The aftermarket supply chain for 6064-series components remains active. Refurbished A20B-2000-0220 boards with tested functionality are available from specialist FANUC drive service providers. Board-level repair — replacing the failed sub-assembly on the board itself — is another option for providers with component-level repair capability.
For machines with long remaining service life, a spindle drive upgrade to a current-generation FANUC serial spindle (6096 or current SPM series) is also technically feasible, though it requires CNC-side parameter changes and confirmation that the CNC controller supports the newer drive's interface.
Assess the machine's total remaining value and expected production life before committing to a complete drive upgrade.
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