LG SN4A User manual

SERVICE MANUAL
SERVICE MANUAL
CAUTION
BEFORE SERVICING THE UNIT, READ THE “SAFETY PRECAUTIONS”
IN THIS MANUAL.
MODEL: SN4A(SN4A, SPN4BM-W)
P/NO : AFN30064620 JULY, 2021
MODEL: SN4A
(SN4A, SPN4BM-W)
Copyright © 2021 LG Electronics Inc. All rights reserved.
Only for training and service purposes.
Wireless Sound Bar
“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.”

1-1
Copyright © 2021 LG Electronics Inc. All rights reserved.
Only for training and service purposes.
CONTENTS
SECTION 1 ........ GENERAL
SECTION 2 ........ CABINET & MAIN CHASSIS
SECTION 3 ........ ELECTRICAL
SECTION 4 ........ WIRELESS SUBWOOFER PART

1-2
Copyright © 2021 LG Electronics Inc. All rights reserved.
Only for training and service purposes.
SECTION 1
SUMMARY
CONTENTS
PRODUCT SAFETY SERVICING GUIDELINES FOR AUDIO PRODUCTS.................................................... 1-3
SERVICING PRECAUTIONS ............................................................................................................................ 1-4
• GENERAL SERVICING PRECAUTIONS
• INSULATION CHECKING PRODEDURE
• ELECTROSTATICALLY SENSITIVE (ES) DEVICES
LOCATION OF CUSTOMER CONTROLS........................................................................................................ 1-5
WIRELESS SUBWOOFER CONNECTION....................................................................................................... 1-6
HIDDEN KEY MODE ......................................................................................................................................... 1-7
SOFTWARE UPDATE GUIDE........................................................................................................................... 1-8
SPECIFICATIONS ........................................................................................................................................... 1-15

1-3
Copyright © 2021 LG Electronics Inc. All rights reserved.
Only for training and service purposes.
PRODUCT SAFETY SERVICING GUIDELINES
FOR AUDIO PRODUCTS
IMPORTANT SAFETY NOTICE
This manual was prepared for use only by properly trained audio-video service
technicians.
When servicing this product, under no circumstances should the original design be
modified or altered without permission from LG Corporation. All components should
be replaced only with types identical to those in the original circuit and their physical
location, wiring and lead dress must conform to original layout upon completion of
repairs.
Special components are also used to prevent x-radiation, shock and fire hazard.
These components are indicated by the letter “x” included in their component des-
ignators and are required to maintain safe performance. No deviations are allowed
without prior approval by LG Corporation.
Circuit diagrams may occasionally differ from the actual circuit used. This way, imple-
mentation of the latest safety and performance improvement changes into the set is
not delayed until the new service literature is printed.
CAUTION : Do not attempt to modify this product in any way. Never perform cus-
tomized installations without manufacturer’s approval. Unauthorized modifications
will not only void the warranty, but may lead to property damage or user injury.
Service work should be performed only after you are thoroughly familiar with these
safety checks and servicing guidelines.
GRAPHIC SYMBOLS
The exclamation point within an equilateral triangle is intended to alert
the service personnel to important safety information in the service
literature.
The lightning flash with arrowhead symbol within an equilateral
triangle is intended to alert the service personnel to the presence of
noninsulated “dangerous voltage” that may be of sufficient magnitude
to constitute a risk of electric shock.
The pictorial representation of a fuse and its rating within an equilat-
eral triangle is intended to convey to the service personnel the follow-
ing fuse replacement caution notice:
CAUTION : FOR CONTINUED PROTECTION AGAINST RISK
OF FIRE, REPLACE ALL FUSES WITH THE SAME TYPE AND
RATING AS MARKED NEAR EACH FUSE.
SERVICE INFORMATION
While servicing, use an isolation transformer for protection from AC line shock. After
the original service problem has been corrected, make a check of the following:
FIRE AND SHOCK HAZARD
1. Be sure that all components are positioned to avoid a possibility of adjacent com-
ponent shorts. This is especially important on items trans-ported to and from the
repair shop.
2. Verify that all protective devices such as insulators, barriers, covers, shields, strain
reliefs, power supply cords, and other hardware have been reinstalled per the
original design. Be sure that the safety purpose of the polarized line plug has not
been defeated.
3. Soldering must be inspected to discover possible cold solder joints, solder
splashes, or sharp solder points. Be certain to remove all loose foreign particles.
4. Check for physical evidence of damage or deterioration to parts and components,
for frayed leads or damaged insulation (including the AC cord), and replace if
necessary.
5. No lead or component should touch a high current device or a resistor rated at 1
watt or more. Lead tension around protruding metal surfaces must be avoided.
6. After reassembly of the set, always perform an AC leakage test on all exposed
metallic parts of the cabinet (the channel selector knobs, antenna terminals,
handle and screws) to be sure that set is safe to operate without danger of electri-
cal shock. DO NOT USE A LINE ISOLATION TRANSFORMER DURING THIS
TEST. Use an AC voltmeter having 5000 ohms per volt or more sensitivity in the
following manner: Connect a 1500 ohm, 10 watt resistor, paralleled by a .15 mfd
150V AC type capacitor between a known good earth ground water pipe, con-
duit, etc.) and the exposed metallic parts, one at a time. Measure the AC voltage
across the combination of 1500 ohm resistor and .15 mfd capacitor. Reverse the
AC plug by using a non-polarized adaptor and repeat AC voltage measurements
for each exposed metallic part. Voltage measured must not exceed 0.75 volts
RMS. This corresponds to 0.5 milliamp AC. Any value exceeding this limit consti-
tutes a potential shock hazard and must be corrected immediately.
TIPS ON PROPER INSTALLATION
1. Never install any receiver in a closed-in recess, cubbyhole, or closely fitting shelf
space over, or close to, a heat duct, or in the path of heated air flow.
2. Avoid conditions of high humidity such as: outdoor patio installations where dew
is a factor, near steam radiators where steam leakage is a factor, etc.
3. Avoid placement where draperies may obstruct venting. The customer should
also avoid the use of decorative scarves or other coverings that might obstruct
ventilation.
4. Wall- and shelf-mounted installations using a commercial mounting kit must follow
the factory-approved mounting instructions. A product mounted to a shelf or plat-
form must retain its original feet (or the equivalent thickness in spacers) to provide
adequate air flow across the bottom. Bolts or screws used for fasteners must not
touch any parts or wiring. Perform leakage tests on customized installations.
5. Caution customers against mounting a product on a sloping shelf or in a tilted
position, unless the receiver is properly secured.
6. A product on a roll-about cart should be stable in its mounting to the cart.
Caution the customer on the hazards of trying to roll a cart with small casters
across thresholds or deep pile carpets.
7. Caution customers against using extension cords. Explain that a forest of exten-
sions, sprouting from a single outlet, can lead to disastrous consequences to
home and family.

1-4
Copyright © 2021 LG Electronics Inc. All rights reserved.
Only for training and service purposes.
SERVICING PRECAUTIONS
CAUTION: Before servicing the
Audio products
covered by this
service data and its supplements and addends, read and fol-
low the SAFETY PRECAUTIONS.
NOTE: if unforeseen circumstances create conflict between
the following servicing precautions and any of the safety
precautions in this publication, always follow the safety pre-
cautions.
Remember Safety First :
General Servicing Precautions
1. Always unplug the
Audio products
AC power cord from the
AC power source before:
(1) Removing or reinstalling any component, circuit board,
module, or any other assembly.
(2) Disconnecting or reconnecting any internal electrical
plug or other electrical connection.
(3) Connecting a test substitute in parallel with an electro-
lytic capacitor.
Caution: A wrong part substitution or incorrect polarity
installation of electrolytic capacitors may result in an
explosion hazard.
2. Do not spray chemicals on or near this
Audio products
or any
of its assemblies.
3. Unless specified otherwise in this service data, clean elec-
trical contacts by applying an appropriate contact cleaning
solution to the contacts with a pipe cleaner, cotton-tipped
swab, or comparable soft applicator.
Unless specified otherwise in this service data, lubrication
of contacts is not required.
4. Do not defeat any plug/socket B+ voltage interlocks with
which instruments covered by this service manual might be
equipped.
5. Do not apply AC power to this
Audio products
and / or any
of its electrical assemblies unless all solid state device heat
sinks are correctly installed.
6. Always connect the test instrument ground lead to an
appropriate ground before connecting the test instrument
positive lead. Always remove the test instrument ground
lead last.
Insulation Checking Procedure
Disconnect the attachment plug from the AC outlet and turn
the power on. Connect an insulation resistance meter (500V)
to the blades of the attachment plug. The insulation resis-
tance between each blade of the attachment plug and acces-
sible conductive parts (Note 1) should be more than 1Mohm.
Note 1: Accessible Conductive Parts include Metal panels,
Input terminals, Earphone jacks,etc.
Electrostatically Sensitive (ES) Devices
Some semiconductor (solid state) devices can be damaged
easily by static electricity. Such components commonly are
called Electrostatically Sensitive (ES) Devices. Examples
of typical ES devices are integrated circuits and some field
effect transistors and semiconductor chip components.
The following techniques should be used to help reduce the
incidence of component damage caused by static electricity.
1. Immediately before handling any semiconductor compo-
nent or semiconductor-equipped assembly, drain off any
electrostatic charge on your body by touching a known
earth ground. Alternatively, obtain and wear a commer-
cially available discharging wrist strap device, which should
be removed for potential shock reasons prior to applying
power to the unit under test.
2. After removing an electrical assembly equipped with ES
devices, place the assembly on a conductive surface such
as aluminum foil, to prevent electrostatic charge buildup or
exposure of the assembly.
3. Use only a grounded-tip soldering iron to solder or unsolder
ES devices.
4. Use only an anti-static solder removal device. Some solder
removal devices not classified as “anti-static” can generate
electrical charges sufficient to damage ES devices.
5. Do not use freon-propelled chemicals. These can generate
an electrical charge sufficient to damage ES devices.
6. Do not remove a replacement ES device from its protective
package until immediately before you are ready to install
it. (Most replacement ES devices are packaged with leads
electrically shorted together by conductive foam, aluminum
foil, or comparable conductive material).
7. Immediately before removing the protective material from
the leads of a replacement ES device, touch the protective
material to the chassis or circuit assembly into which the
device will be installed.
Caution: Be sure no power is applied to the chassis or cir-
cuit, and observe all other safety precautions.
8.Minimize bodily motions when handling unpackaged
replacement ES devices. (Normally harmless motion such
as the brushing together of your clothes fabric or the lifting
of your foot from a carpeted floor can generate static elec-
tricity sufficient to damage an ES device.)

1-5
Copyright © 2021 LG Electronics Inc. All rights reserved.
Only for training and service purposes.
LOCATION OF CUSTOMER CONTROLS
Front panel
Rear panel
Display Window
- Display window will be darkened automatically if there is no key input for 15 seconds.
When you press any button, the display window will brighten.
Remote sensor
(Standby)
- Switches the unit ON or OFF.
F(Function)
- Select the function and input source by pressing Frepeatedly.
Input source / Function Display
Optical, ARC, LG Sound Sync (Wired) OPT/HDMI ARC
Bluetooth BT
LG Sound Sync (Wireless) LG TV
HDMI IN HDMI
USB USB
+/−(Volume)
- Adjusts volume level.
DC IN
- Connect to the AC adapter.
OPTICAL IN
- Connect the OPTICAL IN jack on the back of
the unit to OPTICAL OUT jack on the TV.
HDMI IN
- Connect HDMI IN jack on the back of the unit
to HDMI OUT jack on the external device.
You can enjoy the sound and picture from
HDMI connection on an external device.
HDMI OUT (TV ARC)
- Connect the HDMI OUT (TV ARC) jack on the
back of the unit to ARC jack on the TV.
USB Port
- Connect USB memory device to the USB port
on the back of the unit.
1
2
3
1
24
3 5

1-6
Copyright © 2021 LG Electronics Inc. All rights reserved.
Only for training and service purposes.
WIRELESS SUBWOOFER CONNECTION
LED indicator of wireless subwoofer
LED Color Status
Yellow - green
(Blink)
The connection is trying.
Yellow - green The connection is completed.
Red
The wireless subwoofer
is in standby mode
or the connection is failed.
Off
(No display)
The power cord of wireless
subwoofer is disconnected.
Setting up the wireless subwoofer
for the first time
1. Connect the power cord to the subwoofer and plug
the power cord into a power outlet.
2. Turn on the main unit : The sound bar and wireless
subwoofer will be automatically connected.
- Yellow - green on the rear of wireless subwoofer
turns on.
Manually pairing wireless subwoofer
When your connection is not completed, you can
check red LED on the wireless subwoofer and the
wireless subwoofer does not make sound. To solve
the problem, follow the steps below.
1. Press PAIRING button on the rear of the wireless
subwoofer.
- The yellow - green LED on the rear of the wireless
subwoofer blinks quickly. (If the green LED does
not blink, press and hold the PAIRING.)
2. Turn on the sound bar.
- Pairing is completed. The yellow - green LED on
the front of the wireless subwoofer turns on.
Note
:
•It takes a few seconds (and may take longer) for the
main unit and the subwoofer to communicate with
each other and make sounds.
•The closer the main unit and the subwoofer, the
better sound quality. It is recommended to install the
main unit and the subwoofer as close as possible
and avoid the cases below.
- There is a obstacle between the main unit and the
subwoofer.
- There is a device using same frequency with this
wireless connection such as a medical equipment,
a microwave or a wireless LAN device.
- Keep the sound bar and the subwoofer away from
the device (ex. wireless router, microwave oven,
etc.) over 1m to prevent wireless interference.
XG

1-7
Copyright © 2021 LG Electronics Inc. All rights reserved.
Only for training and service purposes.
HIDDEN KEY MODE
HIDDEN MODE KEYS
EEPROM OPTION EDIT Main unit 'VOL-' + Remote Control ' '
EEPROM CLEAR (Initialize) Main unit 'VOL-' + Remote Control ' '
VERSION CHECK Main unit 'VOL-' + Remote Control 'Play/Pause'

1-8
Copyright © 2021 LG Electronics Inc. All rights reserved.
Only for training and service purposes.
1. Preparation
1) SN4 Series Units : Main Unit, Wireless Subwoofer Unit.
2) SN4 RCU.
3) USB Memory.
4) Android Device with “Music Flow Bluetooth” App for FOTA update, “Version Check APP” for Version Check.
Caution
:
•Take care not to power off during update.
•Do format USB memory before update (FAT32 file system).
SOFTWARE UPDATE GUIDE
<Main Unit>
Necessary
<RCU>
Necessary
<Wireless Subwoofer Unit>
If wireless subwoofer rx module
of primary unit is updated
<USB Memory>
for USB update
<Android Device>
“Music Flow Bluetooth”
must be installed for FOTA update
“Version Check APP”
must be installed for Version Check

1-9
Copyright © 2021 LG Electronics Inc. All rights reserved.
Only for training and service purposes.
2. Using USB
Step 1. Prepare SN4 update binaries.
Update module Prefix & Extension Filename Sample
B/E MAIN_SN4*.ROM MAIN_SN4_BAR_1812170_PRO1.ROM
Micom MICOM_SN4*.HEX MICOM_SN4_1905220_A4A3_rev1901.HEX
Wireless Subwoofer Tx WOOFERTX_SN4*.BIN WOOFERTX_SN4_BAR_190007_PRO1_CHECKSUM_C7CA.bin
Wireless Subwoofer Rx WOOFERRX_SN4*.BIN WOOFERRX_SN4_BAR_191008_PRO1_CHECKSUM_90BE.bin
MEQ MEQ_SN4*.BIN MEQ_SN4_161221B0.BIN
PEQ PEQ_SN4*.BIN PEQ_SN4_171016.BIN
Option OPT*.BIN OPTION_SN4.BIN
Step 2. Copy all updated SN4 binaries to USB memory.
Step 3. Power on SN4 main unit.
Step 4. If there is an updated wireless subwoofer rx binary in update list,
you need to pair between main unit and subwoofer unit before start update.
Step 5. If there is an updated wireless rear rx binary in update list,
you need to pair between main unit and rear speaker unit before start update.
Step 6. Press Function key to change function to USB.
Verify whether USB function is or not by VFD.
Step 7.Attach USB which has update binaries to the USB slot back of SN4 main unit.
Step 8. Update will start automatically.
Check VFD what module is in progress one by one.
※The numbers in VFD display of wireless modules will increase in progress as progress percent from 00 to 100.
(VFD Model)
USB
USB
5 V 500 mA
Update module VFD display
B/E
Micom
Wireless Subwoofer Tx
Wireless Subwoofer Rx
MEQ
PEQ
TOUCH
Option
D-UP
WT 00
M-UP
WR 00
MQ-UP
EQ-UP
T-UP
OP-UP
<SN4 Series VFD Display in Update>

1-10
Copyright © 2021 LG Electronics Inc. All rights reserved.
Only for training and service purposes.
Using USB
Step 9. SN4 main unit will be off automatically after update finish.
Step 10. Power on SN4 main unit again.
Step 11. Check the current versions to verify whether the update was successfully completed or not.
1) Press “Version Check” hidden key
• Version Check Hidden Key : Press Set “Vol-” + RCU “Play/Pause” for 3secs.
2) SN4 shows the version of all modules in the order shown below.
• The order that SN4 shows version in version check hidden mode.
MICOM PEQ B/E MEQ Wireless Subwoofer Tx Wireless Subwoofer Rx
Boot loader (do not mind) Option
3) Compare the version VFD shows and you updated.
+
Module VFD display sample
MICOM
PEQ
B/E
MEQ
Wireless Subwoofer Tx
Wireless Subwoofer Rx
Boot loader
Touch
Option
M1901140
PQ1812030-6326
B1901140
MQ161221
TX190007
RX191008
BL014004
T1910310
00 75 05 93 ...
<SN4 VFD Display in Version Display>

1-11
Copyright © 2021 LG Electronics Inc. All rights reserved.
Only for training and service purposes.
Step 1. Prepare SN4 main unit and Android Device
with “Music Flow Bluetooth”. FOTA Update only sup-
ports B/E(Main) and MICOM module update.
Step 2. Power on SN4 main unit.
Step 3. Execute “Music Flow Bluetooth” App.
Step 4. Connect between android device and SN4
main unit by “Music Flow Bluetooth” App.
3. Using APP (FOTA : Firmware update Over The Air)

1-12
Copyright © 2021 LG Electronics Inc. All rights reserved.
Only for training and service purposes.
Step 5. Check the SN4 current version with “Music
Flow Bluetooth” App.
Step 6. If the main and micom version and of SN4 is
already the latest version, Current version and Latest
version in pop up window “Device version info.” are
same. Also update icon must be disabled.
Using APP (FOTA : Firmware update Over The Air)

1-13
Copyright © 2021 LG Electronics Inc. All rights reserved.
Only for training and service purposes.
Step 7. If the main or micom version of SN4 is not the latest version, Current version and Latest version in pop up
window “Device version info.” are different. Also update icon must be enabled. touch update icon to start FOTA
update.
Step 8. FOTA update will be progress automatically as below sequence.
1) Download binary from server.
2) Transfer binary from Android device to SN4 main unit.
3) SN4 main unit executes update.
1) Download binary 2) Transfer to SN4 3) Update progress
“Music Flow Bluetooth”
App
VFD Model Current Function
Using APP (FOTA : Firmware update Over The Air)
DNLD
D-UP
M-UP

1-14
Copyright © 2021 LG Electronics Inc. All rights reserved.
Only for training and service purposes.
Step 9. SN4 main unit will be off automatically after
update finish.
Step 10. Power on SN4 main unit again.
Step 11. Check the current versions to verify whether
the update was successfully completed in such a way
of Step 5.~ 6.
Using APP (FOTA : Firmware update Over The Air)

1-15
Copyright © 2021 LG Electronics Inc. All rights reserved.
Only for training and service purposes.
SPECIFICATIONS
• GENERAL
Power consumption Refer to the main label on the unit.
AC adapter Model : DA-50F25
Manufacturer : Asian Power Devices Inc.
Input : 100 - 240 V ~ 50 - 60 Hz
Output : 25 V 2 A
Dimensions (W x H x D) Approx. 890.0 mm X 57.0 mm X 85.0 mm With foot
Operating temperature 5 °C to 35 °C (41 °F to 95 °F)
Operating humidity 5 % to 90 %
Bus Power Supply 5 V 500 mA
Available Digital Audio In Sampling Frequency 32 kHz, 44.1 kHz, 48 kHz, 88.2 kHz, 96 kHz
Available Digital Audio In format Dolby Audio, DTS Digital Surround, PCM
• INPUT/OUTPUT
OPTICAL IN 3 V (p-p), Optical jack x 1
HDMI IN 19 Pin (Type A, HDMI™ connector) x 1
HDMI OUT 19 Pin (Type A, HDMI™ connector) x 1
• AMPLIFIER (RMS Output)
Total 400 W RMS
Front 90 W RMS x 2 (4 Ωat 1 kHz, THD 10 %)
Subwoofer 220 W RMS (3 Ωat 80 Hz, THD 10%)
• WIRELESS SUBWOOFER
Power requirements Refer to the main label on the subwoofer.
Power consumption Refer to the main label on the subwoofer.
Type 1 Way 1 Speaker
Impedance 3 Ω
Rated Input Power 200 W
Max. Input Power 400 W
Dimensions (W x H x D) Approx. 171 mm x 390 mm x 261 mm
• Designs and specifications are subject to change without prior notice.

1-16
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Only for training and service purposes.

2-1
Copyright © 2021 LG Electronics Inc. All rights reserved.
Only for training and service purposes.
SECTION 2
CABINET & MAIN CHASSIS
CONTENTS
DISASSEMBLY INSTRUCTIONS ..................................................................................................................... 2-2
1. HOW TO DISASSEMBLE THE MAIN UNIT ............................................................................................. 2-2
EXPLODED VIEWS ........................................................................................................................................... 2-7
1. MAIN UNIT SECTION............................................................................................................................... 2-7
2. WIRELESS SUBWOOFER SECTION.................................................................................................... 2-11
3. PACKING ACCESSORY SECTION ....................................................................................................... 2-15

2-2
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Only for training and service purposes.
DISASSEMBLY INSTRUCTIONS
Figure 1-2
Figure 1-1
1. HOW TO DISASSEMBLE THE MAIN SET
2) Remove the Case Bottom Assembly.
1) Remove the 19 screws.

2-3
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Only for training and service purposes.
Figure 1-4
Figure 1-3
HOW TO DISASSEMBLE THE MAIN SET
4) Remove the SPK Chamber L/R Assembly.
3)
Remove the 2 screws, Disconnect the Harmess/FFC cables (KEY, SPK) and Remove the Main PCB Assembly.
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