Fanuc Power Supply Drive Control PCB CNC Circuit Board A16B-1212-0901

FANUC A16B-1212-0901 | Power Supply A1 (C1 Type) — Series 16/18 CNC Main Rack / 200V / 0.91 kg

The A1 Power Supply — What It Powers and Why the Battery Inside Matters

The A16B-1212-0901 is the C1 type PSU A1 that fits into the 2-slot main rack of FANUC Series 16 and 18 CNC controls — the compact control format used on lathes, machining centres, and EDMs built around these controller generations. It sits in the rack adjacent to the main CPU board and the I/O board, and it powers all the boards in that rack.

This power supply has a built-in I/P unit — an integrated input power relay circuit that manages the CNC power-on and power-off sequence. The relay interlock between the external emergency stop circuit and the CNC's internal power-on logic runs through this unit.

The backup battery is physically inside this PSU — not on the main CPU board. That battery maintains the SRAM data on the main CPU board (CNC parameters, programmes, tool offsets) whenever the CNC is powered off. This has a direct consequence for replacement: if the A16B-1212-0901 is removed from the rack for more than approximately 30 minutes, the battery can no longer supply the CPU board SRAM, and stored data may be lost. Keep the original unit installed until the replacement is ready to be fitted. If the power supply has been out for an extended period before arrival, verify that the CNC data is still intact from a current backup before starting the machine.

Key Specifications

Fault Indication and Fuse Locations

Two LEDs on the power supply front face provide immediate status:

PIL (green): Illuminates when AC input power is present at CP1. If PIL is off with machine power on, check the incoming AC supply and the fuse at F1 (200V AC input fuse: Daito GP75).

Red LED: Illuminates when the power supply detects an internal fault. This LED on with PIL also on indicates the power supply is receiving AC but has an internal failure — the PSU requires replacement or repair.

Additional fuses protect the 9" CRT/LCD output (F3) and I/O unit power (F4). The battery used in this PSU is A98L-0031-0012 — not included with the unit and must be ordered separately if the existing battery is depleted.

FAQ

Q1: Why must the original A16B-1212-0901 stay installed until the replacement arrives?

The SRAM backup battery is physically inside this power supply. It continuously supplies the main CPU board's SRAM through the backplane connection. Removing the PSU cuts battery power to the SRAM, and CNC parameter and programme data can be lost within 30 minutes. Keep the original installed until you are ready to immediately fit the replacement.

Q2: The PIL green LED is off and the CNC will not power on. Is the PSU faulty?

PIL off means no AC power at the PSU input. Before assuming a faulty PSU, verify the incoming AC voltage at CP1 with a meter. Check the F1 input fuse (Daito GP75). If AC voltage is present and the fuse is intact but PIL remains off, the PSU's input circuit has failed and the unit requires repair or replacement.

Q3: Which FANUC controls are compatible with the A16B-1212-0901?

The unit fits FANUC Series 16 and 18 first-generation controls in the A and B model variants: 16-MA, 16-MB, 16-TA, 16-TB, 16-W, 18-MA, 18-MB, 18-TA, 18-TB, 18-MC, and 18-TC. Some R-J robot controllers also use this power supply. It fits 2-slot compact rack configurations — not the larger multi-slot racks used by higher-capability CNC configurations.

Q4: What battery does the A16B-1212-0901 use, and how often should it be replaced?

The battery part number is A98L-0031-0012 and is not included with the PSU. FANUC typically recommends replacement every 2–3 years or when the battery alarm appears on the CNC. Replace the battery with the CNC powered on if possible to avoid SRAM data loss — the battery is hot-swappable in the powered state.

Q5: Can the A16B-1212-0901 be repaired, or does it need to be replaced?

Repair is widely available through FANUC CNC PSU repair specialists. Common failure points include the DC output filter capacitors, rectifier stage components, and the relay in the I/P unit. A repaired unit from a specialist with full-load test verification on a working FANUC 16/18 control is a reliable and economical alternative to sourcing a replacement.