LG UltraGear 34GL750 User manual

P/NO :
CHASSIS :
MODEL :
CAUTION
BEFORE SERVICING THE CHASSIS, READ THE SAFETY PRECAUTIONS IN THIS MANUAL.
SERVICE MANUAL
Copyright © 2019 LG Electronics Inc. All rights reserved. Only training and service purposes.
CONFIDENTIAL
P/NO : MFL70211518 (1904-REV00)
LED MONITOR
SERVICE MANUAL
LM71C
34GL750 34GL750-BB
Any reproduction, duplication, distribution (including by way of email, facsimile or other electronic means),
publication, modification, copying or transmission of this Service Manual is STRICTLY PROHIBITED unless you
have obtained the prior written consent of the LG Electronics entity from which you received this Service Manual.
The material covered by this prohibition includes, without limitation, any text, graphics or logos in this Service
Manual.

- 2 - Copyright © LG Electronics Inc. All rights reserved.
Only training and service purposes.
CONTENTS .............................................................................................. 2
SAFETY PRECAUTIONS ........................................................................ 3
SPECIFICATION ....................................................................................... 4
ADJUSTMENT INSTRUCTION ................................................................ 6
BLOCK DIAGRAM ................................................................................... 7
EXPLODED VIEW .................................................................................... 8
DISASSEMBLY ........................................................................................ 9
TROUBLE SHOOTING GUIDE .............................................................. 11
CONTENTS

- 3 - Copyright © LG Electronics Inc. All rights reserved.
Only training and service purposes.
Many electrical and mechanical parts in this chassis have special safety-related characteristics. These parts are identified by in the
Exploded View.
It is essential that these special safety parts should be replaced with the same components as recommended in this manual to prevent
Shock, Fire, or other Hazards.
Do not modify the original design without permission of manufacturer.
General Guidance
An isolation Transformer should always be used during the
servicing of a receiver whose chassis is not isolated from the AC
power line. Use a transformer of adequate power rating as this
protects the technician from accidents resulting in personal injury
from electrical shocks.
It will also protect the receiver and it's components from being
damaged by accidental shorts of the circuitry that may be
inadvertently introduced during the service operation.
If any fuse (or Fusible Resistor) in this TV receiver is blown,
replace it with the specified.
When replacing a high wattage resistor (Oxide Metal Film Resistor,
over 1 W), keep the resistor 10 mm away from PCB.
Keep wires away from high voltage or high temperature parts.
Before returning the receiver to the customer,
always perform an AC leakage current check on the exposed
metallic parts of the cabinet, such as antennas, terminals, etc., to
be sure the set is safe to operate without damage of electrical
shock.
Leakage Current Cold Check(Antenna Cold Check)
With the instrument AC plug removed from AC source, connect an
electrical jumper across the two AC plug prongs. Place the AC
switch in the on position, connect one lead of ohm-meter to the AC
plug prongs tied together and touch other ohm-meter lead in turn to
each exposed metallic parts such as antenna terminals, phone
jacks, etc.
If the exposed metallic part has a return path to the chassis, the
measured resistance should be between 1 MΩand 5.2 MΩ.
When the exposed metal has no return path to the chassis the
reading must be infinite.
An other abnormality exists that must be corrected before the
receiver is returned to the customer.
Leakage Current Hot Check (See below Figure)
Plug the AC cord directly into the AC outlet.
Do not use a line Isolation Transformer during this check.
Connect 1.5 K / 10 watt resistor in parallel with a 0.15 uF capacitor
between a known good earth ground (Water Pipe, Conduit, etc.)
and the exposed metallic parts.
Measure the AC voltage across the resistor using AC voltmeter
with 1000 ohms/volt or more sensitivity.
Reverse plug the AC cord into the AC outlet and repeat AC voltage
measurements for each exposed metallic part. Any voltage
measured must not exceed 0.75 volt RMS which is corresponds to
0.5 mA.
In case any measurement is out of the limits specified, there is
possibility of shock hazard and the set must be checked and
repaired before it is returned to the customer.
Leakage Current Hot Check circuit
IMPORTANT SAFETY NOTICE
To Instrument's
exposed
METALLIC PARTS
Good Earth Ground
such as WATER PIPE,
CONDUIT etc.
AC Volt-meter
SAFETY PRECAUTIONS

- 4 - Copyright © LG Electronics Inc. All rights reserved.
Only training and service purposes.
SPECIFICATION
Item Content Remark
1 Customer BRAND
2 User Model Name 34GL750
3 Sale region World Wide
4 Feature 34” WFHD 144Hz Monitor
5 Chassis Name LM61C
6 General Scope External SW &Adj. Joystick Power off , Menu, Game Mode, Input, Close
Hot Key Gamer1, Gamer2, FPS1, FPS2, RTS,
Reader
Function Game Mode, Aspect Ratio, S.E.S, On Screen Control
7 Power Code Length 1.00±0.04M Refer to Suf-
power cord table
Weight 0.13kg±10%,
Color Black
8 Cable DisplayPort Length 1.5±0.05 M
Weight 0.095kg±10%,
Color Black
Impedance 1) Cable : 100Ω±5Ω,
2) Connector : 100Ω±5Ω
HDMI Length 1.5±0.05 M
Weight 0.0887kg±10%,
Color Black
Impedance 1) Cable : 100Ω±5Ω,
2) Connector : 100Ω±5Ω
9 Power
(Adapter) Output: DC 19V 3.42A,65W Adapter
Color : Black, Weight : 0.205kg±10%

- 5 - Copyright © LG Electronics Inc. All rights reserved.
Only training and service purposes.
2. Signal Timing (Resolution)
2.1. Signal (Video & Sync)
2.2. H/V Timing
mode
section
polarity
DOT
CLOCK
[MHz]
Frequenc
y
[kHz]/[Hz]
Total
Period(E
)
Display
(A)
Front
Porch
(D)
Sync.
(C)
Back
Porch
(B)
Resolution
1
H(Pixels)
-
25.175
31.469
800
640
16
96
48
640 x 480
V(Lines)
-
59.94
525
480
10
2
33
2
H(Pixels)
+
40.00
37.879
1056
800
40
128
88
800 x 600
V(Lines)
+
60.317
628
600
1
4
23
3
H(Pixels)
-
65.00
48.363
1344
1024
24
136
160
1024 x 768
V(Lines)
-
60.0
806
768
3
6
29
4
H(Pixels)
+
115.50
97.551
1184
1024
48
32
80
1024 x 768
V(Lines)
-
119.989
813
768
3
4
38
5
H(Pixels)
+
144.00
109.756
1312
1152
48
32
80
1152 x 864
V(Lines)
-
119.952
915
864
3
4
44
6
H(Pixels)
+
131.75
91.493
1330
1280
48
32
80
1280 x 720
V(Lines)
-
119.912
763
720
3
5
35
7
H(Pixels)
+
187.25
130.035
1440
1280
160
112
248
1280x1024
V(Lines)
-
119.958
1066
1024
1
3
38
8
H(Pixels)
+
174.50
83.894
2080
1920
48
32
80
1920x1080
V(Lines)
-
74.973
1119
1080
3
5
31
9
H(Pixels)
+
235.50
113.221
2080
1920
48
32
80
1920x1080
V(Lines)
-
99.930
1133
1080
3
5
45
10
H(Pixels)
+
285.50
137.26
2080
1920
48
32
80
1920x1080
V(Lines)
-
119.98
1144
1080
3
5
56
11(1)
H(Pixels)
+
193.00
68.93
2800
2560
48
32
160
2560x1080
V(Lines)
-
59.94
1150
1080
10
10
50
12
H(Pixels)
+
243.00
86.79
2800
2560
48
32
160
2560x1080(only HDMI1.4和D
P)
V(Lines)
-
74.94
1158
1080
10
10
38
13
H(Pixels)
+
308.00
113.24
2720
2560
48
32
80
2560x1080(Only DP)
V(Lines)
-
99.94
1133
1080
12
10
31
14
H(Pixels)
+
368.83
135.60
2720
2560
48
32
80
2560x1080（only HDMI 2.0
和DP）
V(Lines)
-
120
1130
1080
12
10
28
15
H(Pixels)
+
442.60
162.72
2720
2560
48
32
80
2560x1080（only HDMI 2.0
和DP）
V(Lines)
-
144
1130
1080
12
10
28

- 6- Copyright © LG Electronics Inc. All rights reserved.
Only training and service purposes.
BLOCK DIAGRAM
EEPROM
24C02
MUX
G-SYNC Module
W FHD Panel
2560 * 1080@144Hz
166Hz(O/clock)
U S B3.0 Hub
Down1
Down2 Down3 Down4
Ups tream
Micom
(Front panel MCU)
DP in
A Ch
TMDS
D P : HBR2 DP
DP BCh
DP T ra nsmitter
LVDS e - DP (lower)
Ma s ter: HBR1
LVDS out(0-3) LVDS out(4-7)
Re-Driver
H D MI to DP
Converter
204p SODIMM SOCKET
I2S out
H/P AMP
H/P OUT
SSTx/Rx
LED Driver IC
LED Driver IC
UART
BL LED CTRL_R
I2C
U S B 3 .0 D N ( Q/C)
BL CTRL BL LED CTRL_L
Joystick C o nt r ol
(M NT BTN)
EEPROM
( P a n el d at a,
S/N, H DC P,
u ser setting)
EE_I2C
I2S
FPGA_I2C
E E_I2C
I2C
LV SHT
I 2 C _ CT L
HDMI_DDC
F P G A_ I2 C
I2C
Key0 / key1(ADC)
USB3.0 UP
S E L2
D P / H D MI SE L
I2C
I2C
A UX _I2C
I2C
UART
DP T ra nsmitter e- D P( Up per)
S l ave: HBR1
A UX _I2C
LVDS
S e r ial F l ash
8Mb
S e r ial F l ash
2Mb
S e r ial F l ash
2Mb
U S B 3 .0 D N ( Q/C)
LV SHT
2.5V
3.3V
A d dr: 0xA0
A d dr: 0xA0
A d dr: 0x2 E
A d dr: 0xE0
A d dr: 0xE4
A d dr: 0xE6
SVC port(USB3.0 DN)
SBW
MICOM update
G-SYNC
FPGA update
T r ansmissi on c able
VBUS_DET_2

Copyright © LG Electronics Inc. All rights reserved.
Only training and service purposes.
- -
EXPLODED VIEW
910
900
920
930
510
300
200
500
330
400
LV1
540
A3
Many electrical and mechanical parts in this chassis have special safety-related characteristics. These parts
are identified by in the EXPLODED VIEW.
It is essential that these special safety parts should be replaced with the same components as recommended
in this manual to prevent Shock, Fire, or other Hazards.
Do not modify the original design without permission of manufacturer.
IMPORTANT SAFETY NOTICE

- 8- Copyright © LG Electronics Inc. All rights reserved.
Only training and service purposes.
DISASSEMBLY
1. Preparation
1.1. Preparation tool (jig)
1.2. Tool (Curved Packing in a box)
2. Stand Assembly Separation
1) Put a product on a curved packing
2) Pull a button and disassemble a stand
3) Using a screw Driver, remove screws (4ea)
3. Back cover Assembly
1) Using plastic jig, disassemble a back cover : Sequence is
like a below.
* Detail method
① Bottom corner(Bottom corner)
-Put a jig at the corner
- Using thumb, pull a jig upwards.
①
②
③
④
⑤
⑥
⑦
①
②
③
④
⑤
⑥⑦⑧⑧
⑨
The thumb make it easy.
(the principles of the lever)
: Push a back cover

- 9- Copyright © LG Electronics Inc. All rights reserved.
Only training and service purposes.
- Using thumb, pull a jig upwards.
- Pull a jig upwards - Pull a jig upwards
- Put a jig at the bottom - Pull a jig into the center.
- Put a jig at the top corner
- Pull a jig into the center. (Other hands push up a backcover)
2) After Back Cover separation, disassemble LED Cable and
eDP Cable
3) Disassemble screws(2ea) : Module + Rear shield
4) Disassemble Control PCB Ass’y (Latch Type)
(34UC98/88 model is common structure.)
5) Disassemble screws (10ea) : Module + Cabinet
②Side ③Side ④,⑤Side
⑥Bottom
⑦, ⑧Bottom
⑨Top
Push a latch rib

- 10 - LGE Internal Use OnlyCopyright © LG Electronics. Inc. All rights reserved.
Only for training and service purposes
TROUBLE SHOOTING GUIDE
1. No Power
Replace X100
N
Check C701
Voltage Level (19V)
Check Power connector
OK? Replace Adapter
Y
N Y
Check IC703 Output
Voltage Level (3.3V)
Replace IC703 &
Recheck
Y
N
Check X100 Clock
27MHz
Check IC701, 702 Output
Voltage Level (5V)
Replace IC701, 702 &
Recheck
N
Y
Replace IC107 Flash
Memory
Y
Y
Check IC705 Output
Voltage Level (2.5V, 1.2V)
Replace IC705 &
Recheck
N

- 11 - LGE Internal Use OnlyCopyright © LG Electronics. Inc. All rights reserved.
Only for training and service purposes
2. No Screen on
Replace FFCable
N
Module Back Light On?
Check IC601, IC602
Replace LED Driver IC
Y
N
N
Check Panel Power 10V (L700)
Check IC700 Output 10V
Replace IC700 &
Recheck
Y
N
Check Panel eDP AUX
P300 (#9, 10, 36, 37)
Check IC300, IC303
Repair Main B/D
Y
N
Check FFC Cable for Damage or
Open Conductors
Check LED Driver Output
(P601, P602 -1, 2, 5, 6)
Replace T-Con Board or Module
Y
Check P201 (PIN No.69)
Replace G-SYNC Module
N
Check WLED_ENABLE High?
(IC601,IC602 27pin)
Y
Replace G-SYNC Module
N

- 12 - LGE Internal Use OnlyCopyright © LG Electronics. Inc. All rights reserved.
Only for training and service purposes
3. No Video – HDMI
Replace the G-SYNC Module
Check input signal format
Is it supported?
Check JK102 for proper
connection or Damage Replace the Connector
N
Y
Check HDMI Cable for Damage or
Open Connector
Y
Check I2C Signal
(EDID) Replace the IC100
N
Y
Check IC102 AUX Signal
(#J1,H1) Replace the IC102
N
Y
Check IC103 AUX Signal
(#3,4) Replace the IC103
N
Y
Y

- 13 - LGE Internal Use OnlyCopyright © LG Electronics. Inc. All rights reserved.
Only for training and service purposes
4. No Video – DP
Replace the G-SYNC Module
Check input signal format
Is it supported?
Check JK101 for proper
connection or Damage Replace the Connector
N
Y
Check DP Cable for Damage or
Open Connector
Y
Check IC101 AUX Signal
(#29,30) Replace the IC101
N
Y
Y
Check IC103 AUX Signal
(#3,4) Replace the IC103
N
Y