❓ Question — from a maintenance contractor, Bengaluru
Generic question since we service mixed brands: when a CNC screen goes blank but the machine seems alive (can still cycle-start blind), how do you decide between LCD panel, inverter/backlight, video board and motherboard?
✅ Answer — JJ Automation Technical Team
The torch test answers half of these in 10 seconds:
- Shine a torch at an angle on the dark screen. If you can faintly see the screen contents → the video path is FINE, the backlight (CCFL tube or its inverter) is dead. This is the most common failure on 10+ year old machines. Fix: backlight tube, inverter board, or a modern LED-backlight replacement panel.
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Totally black, no ghost image:
- Check for a cursor flash or boot text at power-on — anything momentary means the panel works and the CNC stops sending video → look at the display/graphic card seating and its connector.
- Measure panel supply (typically 12V/24V at the LCD unit connector). Missing supply → power board or wiring, not the LCD.
- Machine boots normally otherwise? If the CNC itself has alarms/doesn't boot (no keyboard beep, drives not ready), the blank screen is a symptom — suspect the motherboard/CPU, not the display chain.
- Brand notes: Fanuc 0i units integrate LCD+video in the A02B display unit (often swap as one); Mitsubishi M70/M80 use separate display units (FCU8 series); Siemens 828D PPU is one integrated unit — a dead PPU display usually means PPU exchange.
Reply below with brand + model + what the torch test shows and we'll point you to the exact part.
Displays & LCD units in stock: Fanuc Display Spares · Fanuc Display Accessories · Mitsubishi Display Spares · Call +91 88022 12394.