Before you do anything about a Samsung TV showing vertical lines, a half-dark screen, flicker, or black blotches, answer one question: is it the panel or the signal? That single test decides everything — a signal problem is a free fix, a panel problem is a repair. Samsung builds the test right in.
Run the Picture Test first
Settings > Support > Device Care > Self Diagnosis > Picture Test. This plays a reference image generated inside the TV, with no input involved.
- The lines / spots / flicker show up on the Picture Test too → it's the panel or the internal board. No setting or cable will fix it; it's a repair.
- The Picture Test looks perfect → the panel is fine, and the problem is coming from your source, cable, or settings. Keep going below.
If the Picture Test is clean (it's the signal)
- Swap the input and cable. Move the device to a different HDMI port and try a known-good cable. Lines or flicker that follow the cable or port are a connection problem, not the TV — work the HDMI no-signal steps if the input drops out entirely.
- Power-cycle properly. Unplug the TV for at least 30 seconds (this also clears a stuck frame buffer that can freeze half the screen), then plug back in.
- Turn off the processing that causes flicker. In Picture > Expert Settings, switch off Picture Clarity / motion interpolation and local dimming to test — aggressive processing causes flicker and haloing on some sources.
- Match the source's output to the TV. A device pushing a resolution or HDR mode the port can't cleanly handle produces flicker or dropouts. Drop it to a safe mode (1080p or 4K60) and build back up. If the picture is more washed-out than glitchy, it's usually an HDMI/HDR setting rather than the panel.
What each symptom usually means
- A single thin vertical or horizontal line that shows on the Picture Test → a failed panel connection (T-CON board or ribbon cable). Repair.
- Half the screen dark or a different shade → a backlight zone or panel-driver fault if it's on the Picture Test; a source/HDR issue if it's only on one input.
- Flicker → usually motion processing or a marginal cable/source if the Picture Test is clean; a backlight or board fault if it flickers on the test too.
- Black spots or blotches that spread → physical panel damage (pressure or impact). Not fixable by settings.
FAQ
How do I know if it's the panel or just my cable box? Run the Picture Test (Settings > Support > Device Care > Self Diagnosis). If the defect shows on the test, it's the panel; if the test is clean, it's your source or cable.
Lines appeared after I bumped the TV — fixable? Usually not by you. Physical lines that show on the Picture Test mean a panel or ribbon-cable fault, which is a repair.
The screen flickers only on one app or device. That's the source or the cable, not the panel. Swap the cable and port, and turn off motion processing to test.
Will a factory reset fix lines on the screen? No — if they show on the Picture Test, no software change touches them. A reset only helps a settings glitch, which the test rules out.