LG OLED TV F40 Error Code Fix Guide

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What This Error Means

F40 on an LG OLED TV means an internal power/protection fault.

Translation: the TV is seeing bad voltage, a short, or a sick board, so the protection circuit kills power and throws F40 instead of letting the OLED panel fry.

You’ll usually see it when the set tries to start, you hear a click or relay, maybe a logo flash, then it shuts down and shows F40 or just refuses to stay on.

This is almost never caused by your HDMI devices, apps, or picture settings; it’s almost always something inside the TV.

Official Fix

LG’s official playbook is: rule out simple power issues, then schedule service.

  • Unplug the TV from the wall for at least 60 seconds.
  • While unplugged, press and hold the power button on the TV itself (not the remote) for 10–15 seconds to discharge any leftover power.
  • Plug the TV directly into a known-good wall outlet. No power strip, no surge protector, no extension cord.
  • Disconnect everything from the TV: all HDMI, USB, antenna, soundbar, gaming consoles, etc. Try to power it on “naked.”
  • If it stays on long enough, go to Settings → Support → Software Update and install any pending firmware update, then power-cycle it again.
  • Make sure the back of the TV has breathing room. If it’s jammed in a tight cabinet and cooking, overheating can trip protection and trigger fault codes.

If F40 still comes back after this, LG treats it as an internal hardware failure and sends a tech. They’ll meter the power supply and main board, then replace whichever board is failing (often the power supply board, sometimes the main board, sometimes both).

The Technician’s Trick

If it’s out of warranty and you’re decent with tools, here’s how a real tech chases F40 instead of just swapping the whole TV.

If any of this sounds sketchy, stop now and call a pro. There are dangerous voltages inside even after unplugging.

  • Unplug the TV and let it sit at least 5–10 minutes. You want the big capacitors on the power board to bleed down.
  • Lay the TV face-down on a soft, flat surface (blanket, foam, or the shipping box). Remove the stand and all rear screws, then lift the back cover off.
  • Find the power supply board (where the AC cord lands) and the main board (where the HDMI ports are). Do a slow visual scan: burn marks, cracked or bulging capacitors, browned connectors = bad news.
  • Carefully unplug and re-seat every connector between the power board, main board, and panel. Don’t yank; rock them out, then push firmly back in until they fully seat. A half-seated plug can absolutely trigger F-codes.
  • Blow out dust with compressed air, especially around the power board and any vents. Dust = heat, and heat = protection trips.
  • If you know what you’re doing, power the TV briefly with the back still off and watch the boards (hands off). If the power board clicks, the standby light blinks, then it dies instantly, the PSU is the usual suspect. If power stays up but you still get F40/no picture, the main board is more likely.
  • Do NOT poke, tap, or measure anything powered unless you’re trained and using the right meter and probes. You can shock yourself or take the TV out for good.

The “inside trick” is simple: re-seating and cleaning sometimes clears an intermittent F40 for free. If it doesn’t, this process tells you which board to order instead of guessing.

Is It Worth Fixing? (The Financial Verdict)

  • ✅ Fix: TV is under ~6 years old, panel looks good (no burn-in/banding), and a power or main board replacement quote comes in well under half the price of a comparable new OLED.
  • ⚠️ Debatable: Set is 6–8 years old, has mild burn-in or other issues, or you’d have to pay diagnostic plus parts without any warranty on the panel itself.
  • ❌ Replace: Visible panel damage, heavy burn-in, liquid/lightning damage, or repair estimates near a new mid-range OLED price (multiple boards, labor, home visit, etc.).

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