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| Place of Origin | JAPAN |
| Brand Name | FANUC |
| Certification | CE ROHS |
| Model Number | A16B-3200-0491 |
Part Number: A16B-3200-0491
Manufacturer: FANUC Corporation (Japan)
Product Type: Main CPU PCB (Master Board)
PMC Engine: PMC-SB7
Compatible Systems: FANUC Series 0i-B (0i-TB, 0i-MB and compatible)
Maximum Axes: 6
The A16B-3200-0491 is the main CPU board for the FANUC Series 0i-B — also known as the Zero i-B — generation of CNC controllers. This is the master board: the central PCB around which the entire controller is built.
It hosts the processor that executes the CNC motion control software, manages the FSSB servo communication to the amplifiers, and coordinates the PMC-SB7 ladder program that handles machine-level I/O.
Every other board in the 0i-B controller stack either plugs into this board directly or communicates with it through the controller's backplane structure.
The 0i-B was FANUC's second generation of the 0i controller family — the successor to the 0i-A and predecessor to the 0i-C.
It found wide adoption in turning centres (0i-TB) and machining centres (0i-MB) during its production era, fitting well into the cost-sensitive segment of the machine tool market where simplified configuration and proven reliability mattered more than cutting-edge features.
Machines built on the 0i-B platform continue to run production worldwide.
This board is supplied without SMD (surface-mount daughter) modules. The modules — FROM memory, DRAM, SRAM, servo control cards, graphic cards — are configured separately based on the specific machine's software options and axis count.
When replacing this board, the SMD modules from the original board are transferred to the replacement.
| Parameter | Value |
|---|---|
| Part Number | A16B-3200-0491 |
| Manufacturer | FANUC Corporation |
| Product Type | Main CPU PCB (Master Board) |
| Controller Platform | FANUC Series 0i-B (Zero i-B) |
| PMC Engine | PMC-SB7 |
| Maximum Axis Count | 6 |
| Compatible Systems | 0i-TB, 0i-MB and compatible |
| SMD Modules | Not included — transferred from existing board |
| Servo Bus | FSSB (Fiber-optic Servo Serial Bus) |
| Origin | Japan |
| Operating Temperature | 0 – 55°C |
| Storage Temperature | −20 – 60°C |
| Condition Available | New / Refurbished / Repaired |
The PMC-SB7 is the PMC (Programmable Machine Controller) engine integrated into the A16B-3200-0491. It is the hardware platform on which the machine builder's ladder program runs.
On the 0i-B, the PMC-SB7 provided a significant step up from earlier PMC generations — faster scan cycle, larger program capacity, and extended instruction set compared to the PMC-SA5 used on the 0i-A.
The ladder program on an 0i-B turning centre or machining centre is where every machine function is implemented.
Tool changers, coolant systems, spindle gear selection, chuck control, door interlocks, part counters — all of these respond because the PMC-SB7 ladder program processes their input conditions and drives their output actions.
When the CNC executes an M-code, it is the PMC-SB7 that interprets that M-code and activates the corresponding machine hardware.
The -SB7 designation distinguishes this board from the A16B-3200-0490, which hosts the PMC-SA5 engine. Both boards are physically similar but not interchangeable — the PMC software and system software are matched to the specific PMC engine.
A machine configured for PMC-SB7 requires the -0491 board.
The A16B-3200-0491 is the base board. Its capability is defined by what SMD modules are fitted to it. The FROM module determines the software and how much option software can be stored. The SRAM module determines program storage capacity.
The DRAM module affects real-time processing. The servo card determines how many axes the board can control.
When this board is supplied without modules — as is standard for replacement units — the modules from the machine's original board are removed and refitted.
This process requires:
After the module transfer and board replacement, the machine's CNC software, parameters, and programs should already be present on the transferred FROM and SRAM modules. A software reload may still be required if the FROM content was the reason for the board replacement.
The A16B-3200-0491 communicates with the servo and spindle amplifiers through FSSB — FANUC's Fiber-optic Servo Serial Bus. This is a high-speed optical serial link that replaces the older analog and short-wire digital connections of earlier FANUC generations.
All axis position commands, speed references, and encoder feedback data travel over FSSB.
The optical fiber used in FSSB is immune to the electrical noise generated by the servo amplifiers and power switching in the machine cabinet.
This noise immunity was a significant practical benefit in the 0i generation, which brought CNC control into the same cabinet space as high-power servo drives.
The board supports up to 6 axes on the FSSB. In practice, most 0i-TB machines used 2-4 axes and most 0i-MB machines used 3-5.
The 6-axis capacity provided headroom for compound machine configurations.
Q1: The 0i-B machine powers on but does not complete its boot sequence. The display shows an error early in the startup. Is the A16B-3200-0491 the fault?
Early boot failure can originate in the main CPU board, the power supply, the FROM module, or the DRAM module. Note the specific error code or diagnostic LED pattern on the main board at the point where the boot stops. Different codes point to different fault sources.
An LED pattern that stops immediately with no activity after power-on suggests a power or CPU fault.
An error that occurs partway through the boot, after the FROM load begins, points more toward FROM content or DRAM.
Q2: The machine's PMC ladder was recently modified. After the modification, the machine alarms during startup with a PMC error. Could the board be at fault?
A PMC alarm following a recent ladder modification is almost certainly a software issue, not a board fault.
The new ladder may contain an error, or the program may have been written for a different PMC engine capacity (step count, symbol table size) than the PMC-SB7 supports.
Check the PMC error message — it will reference a specific type of fault. Restore the previous ladder from backup and confirm the machine starts correctly; if it does, the issue is in the modified ladder.
Q3: The board is being replaced. Should the SRAM battery be replaced at the same time?
Yes. If the SRAM module carries a lithium backup battery, check its voltage before transferring it to the new board. If the battery is older than three years or shows a voltage below threshold, replace it during the module transfer.
The transfer process takes the SRAM out of circuit temporarily — if the battery is marginal, the SRAM contents may be lost during the transfer. A fresh battery eliminates this risk.
Q4: After board replacement with module transfer, the machine starts but the tool offset table is empty. All axis parameters are correct. What happened?
Tool offsets are stored in SRAM. If the SRAM module was transferred correctly, its contents should be intact. However, if the SRAM backup battery was low and discharged during the module transfer — even briefly — SRAM contents can be lost. Confirm the battery voltage.
Restore the tool offset table from a backup memory card file. This situation reinforces the importance of taking a complete data backup before any board replacement work.
Q5: The 0i-B machine has the -SA5 PMC on its existing board. Can the A16B-3200-0491 (PMC-SB7) be used as a replacement?
No. The PMC engine on the replacement board must match the original. The CNC system software and the PMC ladder are both written for a specific PMC engine.
An -SA5 ladder and system cannot run on an -SB7 board without full software conversion.
The replacement board must be the -0490 variant (PMC-SA5) to match an existing -SA5 system.
Confirm the PMC engine from the installed board's label before sourcing any replacement.
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