FANUC High-Voltage Board A20B-8100-0710 A2OB-81OO-O71O A20B81000710 Lots Of Stock Best Price

FANUC A20B-8100-0710 | LCD Inverter PCB — For Monochrome LCD on FANUC Series 16i-B / 18i-B CNC, A20B-8100 Display Series, Japan Origin

Overview

The FANUC A20B-8100-0710 is one of those components that most engineers never think about until it fails — and when it fails, the symptom is immediately obvious and the machine cannot be operated.

The backlight inverter drives the cold cathode fluorescent lamp that illuminates the LCD panel. No backlight means no visible display. The operator cannot see axis positions, cannot read alarms, cannot navigate menus. 

The machine is effectively shut down from an operator interaction standpoint, even if every other CNC function is running perfectly.

The inverter board is specific to the monochrome LCD version of the 16i-B and 18i-B operator panel. FANUC produced the Series 16i-B and 18i-B display panels in multiple configurations — monochrome at various sizes, and colour at various sizes.

Each configuration uses its own inverter board design, matched to the specific CCFL tube dimensions and required drive parameters of that panel.

The A20B-8100-0710 is the correct inverter for the monochrome variants; fitting it to a colour LCD display would be incorrect and could damage both boards.

The Series 16i-B and 18i-B were produced in large volumes throughout the 2000s and appear in an enormous number of machine tools still running in production globally.

Their operator panels age predictably — the CCFL backlight tube has a finite service life (typically rated at 30,000 to 50,000 hours), and when the tube nears end of life, the inverter is often the next component to be stressed.

Key Specifications

CCFL Inverter Operation — The Physics of LCD Backlighting

A cold cathode fluorescent lamp needs a high-voltage, high-frequency AC signal to ionise the gas inside the tube and sustain the discharge that produces visible light.

The CNC's internal DC power supply (typically 5V or 24V DC logic-level voltages) cannot directly drive a CCFL — the voltage is too low and the signal is DC rather than AC.

The inverter board's job is to transform that low-voltage DC into a high-voltage AC signal appropriate for the specific CCFL tube installed.

The high-frequency switching circuit on the inverter board — typically operating at 40–80 kHz — drives a step-up transformer that raises the voltage to the CCFL's striking and sustaining voltage. 

The output frequency is chosen to be above the range of visible flicker while remaining within the tube's optimal drive characteristics.

When the inverter board fails, the failure mode is usually one of:

No output at all — the switching circuit has stopped oscillating, the transformer has failed open, or the drive IC has failed. Result: completely dark screen.

Dim or flickering output — the switching frequency has drifted, a capacitor has degraded, or the output transformer is on the edge of failure. Result: dim display or visible flicker.

Intermittent output — a component is failing thermally, working when cold and failing when hot. Result: machine runs fine at startup but screen goes dark after 30–60 minutes of operation.

Diagnosing the Inverter vs. the CCFL Tube

The A20B-8100-0710 inverter and the CCFL backlight tube it drives are separate components.

Both can fail independently, and both produce the same symptom: no backlight. Before replacing the inverter board, it is worth confirming which component has actually failed.

Checking the tube: In a dark environment, look at the LCD panel edge-on during power-up. A working CCFL tube produces a faint glow visible from the edge even when the liquid crystal layer is dark. If the glow is present but dim or flickering, the tube may be ageing rather than the inverter having failed.

If there is no glow whatsoever, either tube or inverter has failed.

Voltage check on the inverter output: With appropriate caution (the inverter output can reach several hundred volts AC), measuring the presence of AC output at the CCFL connector with an appropriate instrument confirms whether the inverter is generating output. If output is present but the CCFL does not light, the tube is the failure point. If no output is present, the inverter is suspect.

Replacing the inverter is simpler than replacing the CCFL tube, because the inverter is a PCB that plugs into the display unit — no custom tube length or socket matching is required.

For machines where the tube has simply aged, specialist CCFL replacement services are available that avoid the cost of a complete LCD panel replacement.

FAQ

Q1: The CNC operator panel screen went dark after the machine had been running for about an hour. After power-off and cool-down, the screen works again for another hour before going dark again. Is this the inverter?

Intermittent failure with thermal dependence is a classic inverter failure pattern.

As the inverter's components heat up during operation, a degraded electrolytic capacitor loses capacitance, a switching transistor increases junction temperature, or solder joints with thermal fatigue cracks open. 

The inverter cannot sustain oscillation and the backlight goes dark. After cool-down, the components contract and the fault clears temporarily. 

Replace the inverter board. If the problem returns with a new inverter, the CCFL tube may also be ageing — a failing tube puts increased stress on the inverter's output stage.

Q2: The screen is completely dark from first power-on. The CNC is otherwise functional — alarms respond to keyboard input. Is the inverter the likely fault?

A dark screen from cold start with otherwise functional CNC strongly suggests the display backlight circuit rather than the display electronics.

Confirm by connecting a PC to the CNC via RS-232C and verifying that the CNC responds correctly to DNC commands — this confirms the control is running. 

The fault is then confined to the display's backlight supply. Check the 24V DC input to the LCD unit (power to the LCD panel housing) before assuming the inverter has failed — a blown fuse or lost power to the panel produces the same symptom.

Q3: Can the A20B-8100-0710 be used on the colour LCD display versions of the 16i-B/18i-B?

No. The A20B-8100-0710 is specified for monochrome LCD panels. Colour LCD displays use different inverter boards (A20B-8001-0920 for 10.4-inch colour, A20B-8001-0922 for 8.4-inch colour) because the colour panels use different CCFL tube configurations and different drive parameters.

Installing the wrong inverter for a colour display would produce incorrect output voltage or frequency for the colour panel's tubes, potentially damaging both the inverter and the CCFL tubes.

Q4: After replacing the A20B-8100-0710, the backlight comes on but is noticeably dimmer than before. What causes this?

A dimmer-than-normal backlight after inverter replacement can have two causes. First, if the replacement board came from a machine where the CCFL tube was ageing, and the tube's drive resistance has increased, the inverter compensates by outputting more power — but a fresh inverter on an ageing tube will reproduce the dim symptom.

The tube needs replacement too.

Second, if the replacement inverter's output frequency or voltage is not precisely matched to this specific LCD type, brightness may differ slightly from original. Verify the replacement board's part number exactly matches A20B-8100-0710.

Q5: The operator panel housing needs to be opened to access the A20B-8100-0710. What precautions apply?

Before opening the LCD/MDI panel housing, power down the CNC completely and verify mains isolation. The inverter board generates high-voltage AC at its CCFL output connector — this connector should be disconnected before the board is handled.

After disconnecting power and the CCFL connector, wait 30 seconds to allow any residual charge in the inverter's output capacitors to discharge before touching the board or connectors. Handle the replacement board with an ESD wrist strap.

When reconnecting, ensure the CCFL connector is correctly seated — a reversed or partially connected CCFL cable can damage the new inverter board immediately on power-up.