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| Place of Origin | JAPAN |
| Brand Name | FANUC |
| Certification | CE ROHS |
| Model Number | A16B-3200-0425 |
Part Number: A16B-3200-0425
Manufacturer: FANUC Corporation (Japan)
Product Type: Main CPU PCB (Separate / Standalone)
Board Series: A16B-3200
Description: PCB — F21i-B DPL Separate Main CPU
Compatible Systems: FANUC Series 21i-B CNC controllers
Application: Central processing board for Series 21i-B CNC
The A16B-3200-0425 is the main CPU PCB for FANUC's Series 21i-B CNC — the "F21i-B DPL Separate Main CPU" that serves as the central processing core of the 21i-B controller.
The 21i-B is FANUC's compact, cost-effective i-series CNC platform, positioned for small to mid-sized machine tools where the full capability of the 16i or 18i is not required but the high reliability and machining performance of the i-series architecture is desired.
The "separate" designation in the board's description indicates this is the standalone main CPU board — a distinct board design from the display-integrated versions where the CPU and display electronics share a single PCB.
In the DPL (Display) separate configuration, the main CPU board handles all controller processing independently, connecting to the display unit through defined interface connections.
This separation simplifies replacement: the CPU board can be changed independently of the display hardware.
The A16B-3200 series is FANUC's family of main CPU boards spanning multiple i-series CNC and robot controller generations.
Within this family, the A16B-3200-0425 is specific to the 21i-B platform. It is the board that runs the CNC's operating software, executes the PMC ladder logic, manages memory and I/O interfaces, and coordinates all controller functions through the backplane.
| Parameter | Value |
|---|---|
| Part Number | A16B-3200-0425 |
| Manufacturer | FANUC Corporation |
| Product Type | Main CPU PCB (Separate) |
| Board Series | A16B-3200 |
| Description | F21i-B DPL Separate Main CPU |
| Compatible Systems | FANUC Series 21i-B CNC |
| Application | Core controller processing |
| Origin | Japan |
| Operating Temperature | 0 – 45°C |
| Storage Temperature | −20 – 60°C |
| Condition Available | New (surplus) / Refurbished / Repaired |
FANUC's Series 21i-B is part of the i-B series generation — the second iteration of the i-series architecture that followed the original i-A models.
The 21i designation indicates FANUC's compact-class i-series platform, optimised for machine tools that require the i-series quality and reliability but can work within a smaller axis count and feature set compared to the 16i and 18i.
The 21i-B serves lathes, small to mid-sized machining centres, and multi-function machines where the typical configuration involves two to four controlled axes.
The controller's programming environment — standard G-code, FANUC macro B, and the familiar operator interface — is identical to the larger i-series platforms, ensuring that part programs and operator procedures transfer between machine types without retraining.
The main CPU board is the most critical single component in this controller.
Everything the controller does — motor interpolation, PMC execution, operator panel response, program storage access, communication with servo amplifiers — flows through this board. When it fails, the controller does not function, and the machine it controls stops completely.
The "DPL Separate" designation provides a key distinction about this board's architecture. In earlier and some alternative controller configurations, the CPU electronics and the display control electronics were combined on a single motherboard.
The display panel connected directly to this combined board.
The separate design keeps the CPU processing on one board and the display interface on another.
This has practical maintenance advantages. If the display electronics fail, the CPU board does not need replacement — and vice versa.
If the CPU board fails while the display is functioning, the replacement is targeted to the CPU board alone.
This targeted repair approach reduces both the cost and the lead time for getting the machine running again.
It also allows for different display configurations with the same CPU board — the 21i-B with different display sizes or types can use the same main CPU board, with only the display interface components differing.
Replacing the A16B-3200-0425 requires a data restoration procedure after the hardware change. The new CPU board starts with its FROM containing the factory software — the CNC operating system version appropriate for the 21i-B.
But the machine-specific data — all the parameters that define how the controller behaves for this specific machine, the PMC ladder program that implements the machine's automation logic, and the stored part programs — must be restored from backup.
Before removing the original CPU board, a complete backup of all machine data is essential. FANUC controllers provide backup functions through the boot menu and through the CNC's data I/O functions.
The backup should include CNC parameters, PMC parameters, PMC ladder data, pitch error compensation data, and any stored programs.
With a complete backup available, data restoration after board replacement is a defined process.
Without a backup, recovering the machine to its original state requires rebuilding the parameter set from documentation — a time-consuming process that requires intimate knowledge of the machine's configuration.
Before concluding the A16B-3200-0425 has failed, a structured diagnostic check identifies whether the failure is truly in the main CPU board or in a connected component. Power supply voltages to the board must be within specification — a failing power supply often produces CPU board-like symptoms.
Connector seating must be confirmed — a backplane connector that is partially disengaged can cause the CPU board's bus communication to fail without any fault in the board itself. The FROM/SRAM memory modules mounted on the board should be checked for seating.
If the controller produces an alarm at power-on that identifies a specific function area, the alarm code documentation maps that function to its associated board.
A CPU board failure typically produces alarms that prevent any startup progress — the controller cannot complete its self-check and displays an early-stage error code.
Q1: The 21i-B controller shows a RAM error alarm at power-on after a power failure. Is the A16B-3200-0425 the cause?
A RAM error after a power failure most commonly indicates SRAM data loss due to battery exhaustion — the battery that maintains parameter data during power-off has been depleted. This is a battery failure, not a CPU board failure.
Check the battery voltage and replace if below the retention threshold. Restore parameters from backup.
Only if the alarm persists after battery replacement and parameter restore should the CPU board be suspected.
Q2: After a lightning event, the 21i-B controller does not power on at all. No LEDs illuminate on the main CPU board. Is the board damaged?
Check the controller's power supply unit first. Lightning events frequently damage power supply components through transient overvoltage.
If the power supply is not delivering correct voltages to the CPU board, the board will show no signs of life even if the board itself is undamaged.
Measure the supply voltages at the board's power input before concluding the board is at fault.
Q3: A replacement A16B-3200-0425 was installed and the controller now starts, but several machine functions behave incorrectly. Parameters were restored from backup. What should be checked?
Incorrect machine behaviour after parameter restore suggests either the backup was incomplete (some parameter groups were not captured) or the FROM software version on the replacement board differs from the original.
A different FROM version may have parameter defaults that override some restored values, or may interpret some parameter values differently.
Compare the FROM version on the replacement board against the original. If they differ, loading the correct FROM version is the first step before further parameter troubleshooting.
Q4: The machine is in a remote facility without immediate FANUC support. How can the CPU board fault be confirmed before ordering a replacement?
Confirmation of a CPU board fault without substitute boards available is challenging. Document the exact alarm codes displayed and their sequence during the startup attempt. Check the board's LED indicators — most FANUC CPU boards have diagnostic LEDs that show the stage at which startup fails.
Cross-reference the LED states and alarm codes against the controller's maintenance manual.
The maintenance manual's diagnostic flowcharts for CPU board faults are the most reliable guide to remote diagnosis. Contact FANUC technical support with the complete alarm and LED information.
Q5: Is the A16B-3200-0425 compatible with any Series 16i or 18i controllers, or is it specific to the 21i-B only?
The A16B-3200-0425 is described specifically as the F21i-B DPL Separate Main CPU.
The 16i, 18i, and 21i use different main CPU board specifications within the A16B-3200 series — the electrical architecture, software interface, and peripheral connectivity differ between these controller families.
The A16B-3200-0425 is not compatible with 16i or 18i controllers. Installing it in a non-21i-B controller would result in failure to start and potential hardware conflict.
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