LG 55QNED81SRA Service Manual page 72

Guide to inspecting parts for symptoms of no power / no screen
Check for Power cord connection
Y
LED
Check the front LED
turns on
- Standby mode : Red light turns on
N
- In operation : Off
Check the power cord
connection
Check if the power strip is working properly
Y
Properly connected
N
Re-connect and
check again
Check for Power B/D defects
Turn on the power using a remote control
Bottom front LED turns off
Defective Main B/D or Power B/D
Y
☞ How to measure voltage(1/4)
Normal
Measure the output voltage of
voltage
Power B/D ST-By
Spec : 7.8V
N
Defective Power B/D
Defective Main B/D
Replace Power B/D
☞ How to measure voltage(2/4)
Measure the output voltage of Power B/D
(12VM / 20VS)
☞ How to measure
Y
Normal
Check the input voltage of
Power B/D → Module
voltage
N
Normal
voltage
N
Defective Power B/D
☞ How to measure voltage(3/4)
Measure the output voltage of
PWR_On
Check the supply voltage of Main B/D → Power B/D
Y
Normal Defective Power B/D
voltage
Spec : 3V or higher
N
Replace Main B/D
Replace Power B/D
1 / 1
Check for Main B/D or Module defects
voltage(4/4)
☞ How to check
Y
How to check Main SoC
Check the sound
(Mute key 3 times)
Y
Check Main B/D
Beeping sound
&
Module
N
Defective SoC
[For all models]
Replace Main B/D
If the result comes out 'NG' for each part, make sure to check the connector
between the part and the cable is properly connected.
(Check if the cable connection is normal)
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Only for training and service purposes.
LG TV
OLED TV
 How to check
- Check if the test pattern works
normally
 Criteria
- Normal pattern: Replace Main B/D
- Defective pattern: Replace Module
LED TV_T-Conless
Internalize T-Con → Main B/D
 How to check
- Measure the voltages of 5 points on
T-Con B/D
 Criteria
-
Normal voltage: Replace Module
- Defective voltage: Replace Main B/D
LED TV_T-Con
Distribution completed
 How to check
- Measure the voltages of 5 points
on T-Con B/D
 Criteria
- Normal voltage: Replace Main B/D
- Defective voltage: Replace Module