Sound but no picture (backlight / LED strip test)

The flashlight test tells you in one minute whether the panel is producing an image with no backlight. If you can see a faint image, the LED strips or LED driver are the likely fault; if not, look at T-con or main board.

Cross-checked ~90 min advancedBrands: Samsung, LG, TCL, Vizio, Hisense, Sony, Roku TV

Before you start

LED driver outputs can exceed 100 V DC; only trained techs should measure live.
Backlight repair means removing the panel; LCD glass and OLED panels crack easily. Never open an OLED panel.

Diagnostic steps

Unlock all 4 steps with expected values

Full library + AI assistant for $34.90, one time.

Get lifetime access

OnCall Tech is a reference tool for trained technicians and can make mistakes. Always disconnect power and confirm with the manufacturer's documentation before you work.

More tvs guides

Component test · TV

TV LED backlight strips and LED driver

LED strips are wired in series strings and run from a constant-current driver at high DC voltage (often around 80-200 V total). One dead LED opens the string and the driver shuts down. Test LEDs with a backlight tester, not a meter diode range, and replace all strips as a set.

6 steps ~120 minadvanced

Component test · TV

T-con (timing control) board: board or panel?

The T-con converts video from the main board into the signals that drive the panel rows and columns. Loose ribbons, a blown T-con fuse or a failed T-con cause image faults; lines that stay fixed in the same place usually mean the panel itself.

5 steps ~45 minadvanced

Component test · TV

TV power supply board

The power supply board makes a standby voltage that is always on, then switches on the main rails when the main board sends a power-on signal. Check standby, then the power-on signal, then main rails. The primary side holds a high-voltage charge.

5 steps ~45 minadvanced