LG 55QNED85SQA Service Manual page 46

Standard Repair Process Detail Technical Manual
symptom
Content
Error
A. Video error_Video error, video lag/stop
TUNER input signal strength checking method
Established
date
Revised
date
All settings  Programmes
Programme Tuning & settings  Manual Tuning
When the signal is strong,
use the attenuator
A3

(-10dB, -15dB, -20dB etc.)
A3