Diagnosis
You have sound, which confirms the TV's main processor and power supply are mostly functional. The black screen with audible audio points to a failure in the video signal path between the main board and the LCD panel itself. Since you can hear sound, the backlight is likely on but very dim (you may see a faint glow in a dark room). The most common culprits are a loose connection on the T-Con (Timing Control) board, a failed T-Con board, or a faulty main board not sending the correct video signal.
How to Fix It
First, perform a soft reset: unplug the TV from the wall outlet, hold the physical power button on the TV (if present) for 30 seconds, then plug it back in and power on. If that fails, internal inspection is needed. Unplug the TV for at least one hour. Remove the back cover by unscrewing all screws along the edges. Locate the long, narrow T-Con board; it's mounted near the center top, connected to the main board via a single flat cable and to the LCD panel with two thin, wide ribbon cables. Carefully unplug and firmly reseat the ribbon cable connections on the T-Con board. Reassemble and test.
If That Didn't Work
If reseating cables doesn't help, the T-Con board (part number 6870L-2583A) or the main board (EAX67177504) has likely failed. You'll need to test voltages on the T-Con board's fuses with a multimeter or swap in a known-good board. For most users, the next step is ordering a replacement main board, as it's the more common point of failure and easier to swap. Ensure any replacement board matches your TV's exact model and serial number prefix.
Heads Up
TV internals hold high-voltage charge even when unplugged. Avoid touching the large silver capacitors on the power supply board. Always ground yourself by touching the TV's metal chassis before handling circuit boards, and never touch the gold contacts on the ribbon cables.