LG 42LT770H (CHASSIS:LA2FF) Service Manual ▷ View online
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TROUBLESHOOTING
Power-Up Boot Fail Trouble Shooting guide
No OSD Trouble Shooting guide
Check P2401 All
Voltage Level (3.5V, 12V, 24V)
Y
N
Check Q2407 output Voltage(12V)
Y
Check LVDS Cable
Y
Check LCD Module
Control board
Check power connector and
RL_ON signal OK ?
N
Replace Power Board
Check Q2407 application circuit
Or replace Q2407
N
Replace Cable
N
Check P2401 All
Voltage Level (3.5V, 12V, 24V)
Y
N
Check IC8701 RESET and
UPDATE pin
Y
Check X8700 Clock
32.768MHz
Y
Check IC8701 IIC
Communication status
Y
Check IR input state of IC8701
57pin
Y
Re-download PTC Micom
Check power connector and
RL_ON signal OK ?
N
Replace Power Board
Check switch SW8700, SW8701
N
Check X8700 application circuit
or Replace X8700
Check IIC line or replace IC8701
Check IR board
N
N
N
- 18 -
Analog RF Video Trouble Shooting guide
Check RF cable & signal
Y
Check TU8900 Pin5
(Video output)
Y
Check tuner 5V power R8953
Y
Check tuner 3.3V power L8904
Y
Check tuner 1.8V power IC8900
2pin : 1.8V
Y
Check MTK LVDS output
Replace Tuner.
N
Check IC2404
Replace L8904
Replace IC8900
N
N
N
Replace IC105
N
Replace IC2404
N
Y
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Digital RF Trouble Shooting guide
Check RF cable & signal
Y
Check TU8900 Pin5
(Video output)
Y
Check tuner 5V power R8953
Y
Check tuner 3.3V power L8904
Y
Check tuner 1.8V power IC8900
2pin : 1.8V
Y
Check MTK LVDS output
Replace Tuner.
N
Check IC2404
Replace L8904
Replace IC8900
N
N
N
Replace IC105
N
Replace IC2404
N
Y
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Composite Video Trouble Shooting guide
HDMI Video Trouble Shooting guide
Check input signal format.
Is it supported?
Y
Check AC cable for damage
For damage or open conductor
Y
Check JK3800
Can you see the normal waveform?
Y
Check the input of MTK(IC105).
Measure waveform at C360 because it’s more easy to check.
Can you see the normal waveform?
Y
This board has big problem because Main chip (MTK) have some troubles.
After checking thoroughly all path once again, You should decide to replace MTK or not.
Replace JK3800
N
Check input signal format.
Is it supported?
Y
Check AC cable for damage
For damage or open conductor
Y
Check JK3301/JK3302/JK3303
Can you see the normal waveform?
Y
Check HDCP key NVRAM(IC100)
Power & I2C signal
Y
Check the input of MTK(IC105).
Measure waveform at R323, R324 because it’s more easy to check.
Can you see the normal waveform?
Y
This board has big problem because Main chip (MTK) have some troubles.
After checking thoroughly all path once again, You should decide to replace MTK or not.
Replace JK3301, JK3302, JK3303
N
Replace IC100
N
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