The Tool Desk
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The guidance below is based on official LG USA and Samsung USA support material checked in early October 2026. Menu names and paths change between brands, model years and software generations, so treat the paths as examples and confirm them against your model’s manual.
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Record the symptom before touching the menus
A precise description narrows the diagnosis more than any setting does. Write down the following before you start:
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- Scope: Does the problem appear in every app and channel, in one HDMI input, on one external device, or only in certain content?
- Trigger: Does it change with room lighting, with scene changes, or at a fixed point in playback?
- Identity: The exact model number and software generation. The model number is on the rear label and in the TV’s information screen. Manufacturers give different menu paths for different model years, so this detail decides which instructions apply.
Run the built-in picture test
The picture test generates its own image inside the TV, so it bypasses your cable, device and broadcast. That makes it the first real dividing line between a TV fault and an external cause.
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On Samsung models from newer generations, follow this path:
- Press the Home button and open Settings.
- Select Support, then Device Care, then Self Diagnosis.
- Select Picture Test and follow the on-screen prompts.
- Watch the full test pattern for lines, dots, flicker and colour changes.
Earlier Samsung models use a different Support or Self Diagnosis path, and LG’s path varies by webOS generation. If the labels do not match, search your model’s manual for “Picture Test” or “Screen Self-Diagnosis.” Samsung also notes that some models do not include an HDMI diagnostic, and its HDMI test is designed for cables shorter than 2 m. Longer cables may not produce reliable results.
Read the result and choose the branch
Use the table below to decide where to go next.
| What you observe | What it points to | Next step |
|---|---|---|
| Test image is clean; the problem appears in one app or channel only | Broadcast signal, streaming app or content source | Check whether other apps or channels show the same problem, then contact the provider if it does not clear. |
| Test image is clean; the problem appears on one HDMI input or one device | Source device, HDMI cable, input, or the device’s output settings | Go to the connection checks and the symptom sections below. |
| Lines, dots, flicker or abnormal colour appear on the TV’s own test image | Probable TV fault | Stop adjusting settings and contact manufacturer service. |
| Test image is clean, but brightness or flicker changes with room light or scenes | Automatic brightness or energy-saving features | Adjust or turn off the relevant feature, then compare. |
Understand the picture controls before changing them
Samsung’s current support guide describes the core controls as follows. Names and behaviour can vary by model.
| Control | What it changes | Practical note |
|---|---|---|
| Backlight | How much light the screen produces | The main lever for a dim or overly bright picture. |
| Brightness | Overall screen brightness | Adjust after Backlight, not instead of it. |
| Contrast | Separation between dark and light elements | Too much makes highlights clip; too little flattens the image. |
| Sharpness | Apparent sharpness of edges | Excess sharpening can add artifacts. No universal value is established. |
| Color | Colour saturation | Affects intensity, not hue. |
| Tint | Green-to-red hue balance | Adjust only if skin tones look wrong on a specific source. |
| Digital Clean View | Reduces picture noise | Useful for noisy broadcasts; can soften fine detail. |
Samsung also documents picture clarity controls, HDMI black level, dynamic contrast, colour tone, white balance, gamma, colour space and a reset option. Game Mode is available on select models and may slightly reduce graphics quality in exchange for lower input lag. These advanced controls are worth using only when you know your model, your source and what you are trying to fix.
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LG advises choosing a picture mode for the viewing environment, your preference or the type of video. Its settings guidance, dated 3 September 2026, groups its suggested values as follows:
| Viewing environment | LG picture mode group |
|---|---|
| Bright room with daylight | Natural Light or Vivid |
| Typical indoor lighting | Artificial Light or Standard |
| Dark room, films | Dark Room or Cinema |
LG cautions that the result depends on the TV’s capability, room lighting, screen reflectance, the settings you choose and the content itself. Treat its values as guidance for those named modes on LG sets, not as calibration values for other brands.
Fix a picture that is too dim, too bright or unstable
Start by choosing a picture mode that matches your room, then adjust Backlight and Brightness. If the screen still changes on its own, check the automatic features next:
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- Power Saving Mode: reduces brightness to lower power use.
- Motion Lighting: adjusts backlight with motion on some Samsung generations.
Samsung says these features can change the image based on ambient light or power-saving needs, and that they may make brightness appear to flicker when the room or content changes. Turn off or adjust one feature at a time, and compare the picture after each change. If the built-in picture test itself flickers, the issue is not a setting; follow manufacturer support guidance.
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- Supports HDMI ARC - Sends audio directly from the HDMI jack to a compatible soundbar or AV receiver, removing the need for an extra cable.
Fix lines, dots or missing parts of the picture
If the built-in test shows lines or dots, the problem is in the TV and needs manufacturer inspection. If the test is clean, the cause is more likely to be the connection or the source:
- Turn the TV off, then reseat the HDMI or antenna cable at both ends.
- Check the cable for visible damage, and try a known-working cable.
- Connect the affected device to another input or a different TV if you can, to see whether the fault follows the device.
- Set the aspect ratio to 16:9 or Original. LG’s lines-and-dots guidance, dated 21 September 2026, recommends one of these for the symptoms it covers, and an incorrect ratio can distort the image or create edge artifacts.
Picture settings cannot repair a cracked screen or an internal display fault.
Fix flicker or changing brightness
Run the built-in test first. If flicker follows room light or scene changes but the test is clean, adjust the automatic brightness or energy-saving features described above. If the flicker is on an HDMI source, reseat the cable and use the TV’s HDMI diagnostic where your model includes one. Keep in mind that the diagnostic is designed for cables under 2 m. Flicker that persists on the TV’s internal test image is a service issue.
Fix abnormal or bleeding colours
Use the built-in test to see whether the colour fault appears independently of the external source. If the TV test is normal, check the source device and connection. The HDMI Deep Color setting is the usual cause of colour distortion or lines on external devices, and the correct value depends on the device and model:
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- Seamless streaming: With fast Wi-Fi and apps that launch in a snap, Roku Select Series TVs get you to your entertainment quickly. You get excellent picture quality, clear sound, automatic updates, and more. It’s simple to use. Hard to outgrow.
- TV, simplified: With setup that only takes minutes, a simple-to-navigate Home Screen, and an uncluttered remote control that does all you need—Roku makes it easier to watch the TV you love.
- A world of free entertainment: Enjoy a huge selection of free live TV, news, sports, movies, shows, and much more—all just a click away.
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- LG’s older guidance: a 4K-capable set-top box and HDMI connector should use On. A device that supports only HD (1920×1080) or lower should use Off.
- LG’s newer lines-and-dots guidance (21 September 2026): disable the feature for devices that do not support it.
Confirm your device’s capability in its own manual, then set the option for the affected input. Do not apply a single On or Off rule to every device.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Fix a soft, noisy or oddly sized image
Begin by confirming that the source is sending the resolution and aspect ratio the TV expects. Then adjust Sharpness and noise reduction in small steps. Excess processing changes the look of the image, and the manufacturers’ support material does not establish one numeric value that suits all content. Use Original or 16:9 where it suits the source. If the problem affects only one broadcast or one external device while the built-in test is normal, the signal or content provider may need to be involved.
Check cables and decide whether to replace one
Replacing a cable is a conditional step, not a first fix. Samsung recommends trying a replacement for an external-device cable when lines do not appear on its picture test, and replacing a cable when its HDMI test identifies a problem. LG recommends inspecting connections and trying a spare cable for persistent lines or dots. Choose a replacement based on connector compatibility, the device’s requirements and the cable’s condition, not on price. A new cable cannot correct a defect that appears on the TV’s own test image.
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If you have changed several values and suspect the combination is the problem, reset the picture settings. On Samsung models, go to Settings → Picture → Expert Settings → Reset Picture. A reset restores defaults for the picture settings only. It does not repair a damaged panel or a faulty source connection, so retest after the reset to see whether the symptom remains.
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When to contact manufacturer support
Contact LG or Samsung support when any of the following applies:
- Lines, dots, flicker or colour faults appear on the built-in picture test image.
- The symptom persists after the connection, source and reset checks.
- The screen shows physical damage or a visible defect in the panel.
Before you call, gather the TV model number, software version, serial number and the result of the picture test, including which symptoms appeared. This lets support decide quickly whether the fault needs inspection or repair.
Model, region and date limits
This guidance is based on US support documentation: LG’s settings guidance dated 3 September 2026, its picture-test guidance dated 17 July 2026 and its lines-and-dots guidance dated 21 September 2026, together with Samsung’s US support pages checked 7 October 2026. Paths and feature names differ by model and region. If your menu does not match, check your region’s support page and the exact model manual.
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