Samsung CL21K40MQGXXAZ Service Manual page 21

Alignment & Adjustment
3-5-2 Adjusting the Screen Voltage
1. Select "Power Off →MUTE→1→8→2→Power On " to enter Service Mode.
2. Turn to toshiba pattern
3. Use remocon come into " G2 Adjust" mode by hand or automatically.
4. Turn Screen VR of FBT and confirm the characters below changed to GREEN.
Samsung Electronics 3-9