Diagnosis
The issue is caused by a malfunctioning or overly sensitive Auto Low Latency Mode (ALLM) trigger. The TCL 43S446 is designed to automatically detect "Game" signals from HDMI-CEC compatible devices (like a PS5, Xbox Series X, or certain Android TV boxes) and instantly switch the picture profile to Game Mode to reduce input lag. When this happens during a Netflix session, the TV is misinterpreting a signal pulse from a connected device as a request to enter low-latency mode. Because Game Mode disables several post-processing features—such as motion smoothing (MEMC), noise reduction, and certain color enhancements—the image suddenly looks "weird," often appearing flatter, more jagged, or lacking the cinematic contrast you expect from a 4K stream. This is typically triggered by a "handshake" error where a background device on another HDMI port sends a signal that the S-Class logic board misidentifies as a gaming trigger, causing the TV to flip modes even while the active input is a streaming app. To confirm this is the issue, observe the top-right corner of the screen when the switch happens; you will often see a brief "Game Mode" notification overlay. If the colors shift from a warm, cinematic tone to a cooler, sharper, but less natural look, the ALLM is definitely the culprit.
How to Fix It
To stop the TV from automatically switching modes, you must manually disable the ALLM handshake for each specific HDMI port. Follow these exact steps:
- Press the Settings (gear icon) button on your TCL remote to open the main menu.
- Navigate to Inputs and select the HDMI port currently being used for your streaming device or the port where a console is plugged in.
- Scroll down to Auto Low Latency Mode (ALLM) and toggle the switch to OFF.
- Return to the main Settings menu and go to Picture.
- Select Picture Mode and manually set it to Movie or Standard. This ensures that even if the TV attempts to switch, it is locked into a profile that preserves image quality.
- If you have multiple devices connected (e.g., a soundbar and a console), repeat the ALLM disable process for every active HDMI port to prevent cross-talk triggers.
If That Didn't Work
- Disable HDMI-CEC (T-Link): The TV's T-Link feature allows devices to control each other, but it often sends erroneous "Wake" or "Mode" commands. Go to Settings > System > T-Link and toggle T-Link to OFF. This severs the communication link that often triggers the accidental Game Mode switch.
- Update the Firmware: Inconsistent ALLM behavior on the S446 series is often a software bug. Go to Settings > System > Software Update and check for updates. Ensure you are on the latest build, as TCL frequently releases patches to fix HDMI handshake stability.
- Swap HDMI Cables: Use a high-speed HDMI 2.0 or 2.1 certified cable. A degraded cable can cause "signal noise" that the TV interprets as a mode-change command. Replace the cable on the device that is triggering the switch with a shielded, gold-plated cable to eliminate electromagnetic interference.
- Reset Picture Settings: If the image remains "weird" even after disabling ALLM, the TV may have saved a corrupted profile. Go to Settings > Picture > Advanced Settings > Reset Picture Settings to clear all custom overrides and return to factory defaults.
Heads Up
- Input Lag Warning: Disabling Game Mode will increase input lag. If you actually play games on this TV, you will notice a slight delay between your controller press and the on-screen action. You will need to manually switch back to Game Mode for gaming.
- Power Cycle: After changing ALLM settings, perform a "cold boot" by unplugging the TV from the wall for 60 seconds. This clears the HDMI handshake cache and forces the TV to recognize the new settings.
- Device Compatibility: Some external streaming sticks (like certain Roku or Fire TV models) have their own "Match Content" settings. Ensure your external device is set to "Auto" or "Match" for dynamic range to prevent the TV from fighting with the device over picture settings.