Suddenly completely dead - even fan doesn't work

Hi @osdoctor

Check if the T5A 250V fuse on the power adapter board is OK or not. With the power disconnect from the monitor use an Ohmmeter to check it is tests 0.00 Ohms i.e,. short circuit and not OL or infinte Ohms i.e. open circuit.

If it has blown then there's a reason for this to happen as normally fuses don't fail of their own accord, so further testing on the power board for a start would be required.

Note: Ensure when you get a replacement fuse, that you get a T5A 250 axial fuse and not a 5A 250V axial fuse. The T rating is important, as it signifies that it is a slow blow fuse and not a normal fast acting fuse. If a fast acting fuse was inserted it would blow immediately that the power was connected, due to the high inrush currents that flow, whereas a slow blow fuse will hold for the duration of the inrush current i.e. 5-8mS, before they subsided back to normal.

If you decide to take a chance and simply replace the power adapter board, search online for the LG part number which is on the board. Looking at the image in Step.7 of the ifixit LG UltraFine 5K Teardown guide, showing the AC-DC adapter module the part number is EAY65288601 but this doesn't mean that the same board is used in your monitor so check first.

If your monitor is completely dead, even with known-good cables and power, it's likely a failed internal power supply. Open the monitor (carefully) and check for blown capacitors (bulging/leaking tops), burnt components, or fuse issues. Replace faulty parts if skilled; otherwise, seek professional repair to avoid electrical hazards.