THOMSON MT31AS User manual

1
THOMSON Service Manual
For MT31AS
Product Support Office
2014/6/11
Model:T28ED12DU-01B;T32ED13DU-01B;T24E12DHU-01B;T24
E12DHU-01W

Service manual of MT31AS
Explanation .......................................................................................................................................1
1. Important Information ..................................................................................................................2
1.1. Important Safety Instructions ....................................................................................................2
2. Product Specification ....................................................................................................................4
2.1. Features .....................................................................................................................................4
2.2. USB multimedia playback format...............................................................................................5
2. The physical picture of 28M1300..................................................................................................5
3. The Exploded view of 28M1300....................................................................................................7
4. The Schematic diagram of Main board .........................................................................................7
5. The Test Guides Of Main Board.....................................................................................................7
5.1. Power Unit .................................................................................................................................9
5.2. Back light driver units...............................................................................................................10
5.3. Decode and I/O Units...............................................................................................................11
5.3.1. The flow of low voltage power supply ..................................................................................11
5.3.2 Small signal process ...............................................................................................................14
5.3.3. Control BUS ...........................................................................................................................15
5.4. Module Circuits Test.................................................................................................................16
5.4.1. The audio power amplifier....................................................................................................16
6. Troubleshooting Flow Chart........................................................................................................17
6.1. Green Power LED does not turn on. ........................................................................................17
6.2. Abnormal display .....................................................................................................................18
Attachment 1: Block diagram
Attachment 2: The Schematic diagram of Main board

1
Explanation
This manual has definite generality. The directory of Main board test is aiming at
MT31AS. It is also used in T32ED13DU-01B, T24E12DHU-01B and T24E12DHU-01W.
The test of Main board includes three parts: Power unit, flow of signals and specific
circuits’ explanation. It will be easy to solve the problem when you analyze from
power, signals and specific elements. The part of common fault maintains is a
summarization from our company's daily product. It is in the end of this manual. It
may be helpful to the readers.

Service manual of MT31AS
1. Important Information
1.1. Important Safety Instructions
1. Read and follow all instructions.
2. Keep these instructions.
3. Heed these warnings.
4. Do not block any ventilation openings. Install in accordance with the manufacturer’s
instructions.
5. Do not install near any heat sources such as radiators, heat registers, stoves, or other
apparatus (including amplifiers) that produce heat.
6. Protect the power cord from being walked on or pinched particularly at plugs, receptacles,
and the point where it exits from the component.
7. Do not use this component near water.
8. Only use the attachments/accessories specified by the manufacturer.
9. Clean only with dry cloth.
10. Use only with the cart, stand, tripod, bracket, or table specified by the manufacturer, or sold
with the component. When the TV is placed on a cart, use caution when moving the cart to
avoid injury from tip-over.
11. Warning: To avoid any injury caused by lean of the product, please always ensure the whole
product was place within the table surface in horizontal.
12. Unplug this component during lighting storms or when unused for long periods of time.

Service manual of MT31AS
13. Refer all servicing to qualified service personnel. Service is required when the component is
damaged in any way, such as power supply cord or plug damage, liquid spilled on or objects
failing onto the component, rain or moisture exposure, abnormal operation, or if the
component has been dropped.
14. If an outside antenna or cable system is connected to the product, be sure the antenna or
cable system is grounded so as to provide some protection against voltage surges and
built-up static charges.
15. An outside antenna system should not be located in the vicinity of overhead power lines or
other electrical light or power circuits, or where it can fall into such power lines or circuits.
When installing an outside antenna system, extreme care should be taken to keep from
touching such power lines or circuits as contact with them might be fatal.
16. Wall or Ceiling Mounting –The product should be mounted to a wall or ceiling only as
recommended by the manufacturer.
17. Apparatus shall not be exposed to dripping or splashing, and no object filled with liquids,
such as vases, shall be placed on it.
18. When the MAINS plug is used as the disconnect device, the disconnect device shall remain
readily operable.

Service manual of MT31AS
2. Product Specification
2.1. Features
CHIPSET
MT5531 MT5531+ATBM7811
PANEL
Panel Type
TFT LCD With LED Backlight
Interface
Dual/Single LVDS Interface
Resolution(max)
1920×1080
VIDEO INPUT
ATV
Receiving Range
48.25MHz~863.25MHz
Input impedance
75Ω
Video System
PAL,SECAM
Sound System
BG,DK,I
Max Storage Channels
199CH
DTV
Receiving Range
42MHz~870MHz
Input impedance
75Ω
Modulation System
DVB-T/T2,DVB-C
Channel Bandwidth
6，7，8MHz
Common Interface
Built-In
Max Storage Channels
256CH
PC-RGB
Format
Up to
1920×1080@60Hz
CVBS
Video System
PAL/NTSC/SECAM
Video level
1.0 VP-P±5%
Component
480i, 480p, 576i, 576p, 720p, 1080i, 1080p
HDMI
480i, 480p, 576i, 576p, 720p, 1080i, 1080p
Support MHL
AUDIO INPUT
PC Audio
Earphone Input
0.2 ~ 2.0 VRMS
CVBS Audio
Component Audio
VIDEO OUTPUT
CVBS
Video System
PAL/NTSC/SECAM
Video level
1.0 VP-P±5%
AUDIO OUTPUT
CVBS Audio
Earphone Output
0.2 ~ 2.0 VRMS
Frequency response
100Hz-15KHz @±3dB
Max Output power
2×5W(16Ω) THD+N<10%@1KHz
SPDIF Output
1 Coaxial
POWER
AC Input Requirement
100-240V~
To Panel
5V or 12V
COMB FILTER
3D
DEINTERLACE
3D
KEY FUNCTION
CH+, CH-, VOL+, VOL-, MENU, SOURCE, POWER

Service manual of MT31AS
2.2. USB multimedia playback format
2. The physical picture of 28M1300
Front view:
Media
File Ext.
Codec
Remark
Video
Audio
Movie
.avi
VC1,MPEG-1/2/4,DiviX,H.264
,VP8，AVS
MP3,
WMA,
AAC,
MP2,
PCM,
AC3
Max Resolution And Frame
Rate:1920×1080@30fps
Max Data Rate: 20 Mbps
.mp4
MPEG-1/2/4,DiviX, H.264
.ts/.trp
MPEG-1/2/4,H.264
.mkv/.mov
MPEG-4,H.264
.mpg
MPEG-1/2/4
.rm/.rmvb
RV8, RV9, RV10
COOK
Max Resolution And Frame
Rate: 1280×720@30fps
Max Data Rate:10 Mbps
Music
.mp3
--
MP3
Sample Rate: 32K~48KHz
Bit Rate: 32K~320Kbps
Channel: Mono/Stereo
.wma
--
WMA
Sample Rate: 8K~48KHz
Bit Rate: 128K~320Kbps
Channel: Mono/Stereo
.aac
--
AAC
Sample Rate: 8K~48KHz
Bit Rate: 128K~442Kbps
Channel: Mono/Stereo
Photo
.jpg/.jpeg
Progressive JPEG
Max solution: 1024×768
Baseline JPEG
Maxesolution:15360×8640
.bmp
Non-Interlaced
--
Max Resolution:
9600×6400
.gif
Interlaced
Max Resolution: 1200×800

Service manual of MT31AS
Back view:
Inner view:

Service manual of MT31AS
3. The Exploded view of 28M1300
Please refer to the attachment 1.
4. The Schematic diagram of Main board
Please refer to the attachment 2.
5. The Test Guides of Main Board
The physic picture of main board:

Service manual of MT31AS
The main board can be divided into three parts: Power, BL driver, Decode and input/output.
Power includes EMC, Wave filtering, full wave rectifier and DC-DC power unit. The BL driver use
constant current source realized by the DC-DC to illumine the light. It can supply constant

Service manual of MT31AS
brightness light source for TV. The part of Decode and input/output can realize the input ports for
TV, and decode the signals. The video signals are outputted to panel by LVDS. The sound signals
driver the speaker by AMP. It is easy to solve the problem quickly if you are familiar with the main
board’s elements because you can deduce the issue components by badness phenomenon.
5.1. Power Unit
The power unit’s EMC wave filtering concludes two common mode inductances and a Y
capacitance. That can insulated against electromagnetism interference and avoid interference
from Main board to power grid. The resistance of NTC inspects the abnormal temperature and
can fuse the fuse to protect circuits. Full wave rectifier translates AC into DC. HV receive DC 300V.
The DC-DC unit adopts Fly back structure. MOS control the on/off by the power manage IC.
Transformer open and close intermittently. The main grade coupling voltage will be commutated
to VCC 18V supplying for the power manages IC. The secondary coil voltage will be commutated
to 12V and 40V by diode when the main grade is steady. 12V will be feed backed to PWM IC’s FB
through TL431 and optocoupler after bleeder circuit. It can adjust GATE to output PWM
waveform. And there can have steady 12V finally.
The waveform of HV test point The waveform of secondary coil
The Schematic diagram of high voltage parts

Service manual of MT31AS
The Schematic diagram of secondary coil
5.2. Back light driver units
Back light driver units supply constant currents for LED in module. Constant current source is
designed as DC-DC power. It can realize the brightness of BL adjustable and self-protect by
appropriative BL driver IC. DC-DC unit is realized by L601, D601 and Q601. GATE outputs PWM
control signals to control Q601’s work. L601 outputs to LED+ by charge and discharge in sequence.
And it promotes VLED outputting by Power to LED+, so as to illume the LED. Specific PWM signal
is generated by BL driver IC. The IC is controlled by BL_ON and DIM. The voltage will be promoted
when BL_ON is in high voltage level. LED- feedback is adjusted by DIM duty ratio lineally so the
brightness is adjustable. +12V_POWER is the supply for IC. The driver ability is set by the
periphery such as ISET and ISENSE. OVP watch the rise of LED+ by the bleeder to avoid the
damage caused by the immense rise of voltage when circuits work normally. LED 1,2,3,4 are LED-
watching the current of LED, and feedback to GATE driver signals to realize to constant current
drive.

Service manual of MT31AS
The waveform of MOS’S
The Schematic diagram of BL driver
5.3. Decode and I/O Units
5.3.1. The flow of low voltage power supply
Checking the low voltage power supply is principal step when you are maintaining the
badness. It’s meaningless to analyzing the circuits without affirming the power supply is OK.
Referring the flow of low voltage power supply, the Decode and I/O units get +12V power from
the power unit. Each voltage of the elements need is transformed from +12V by DC-DC and LDO.
Switch IC and MOS switch circuits can control the supply current in real time to insure the Main
board work normal.

Service manual of MT31AS
The flow of low voltage power supply
Test the power supply of Main board when power is on. Test the DS1’s cathode voltage to
GND is +12V for debarring the power unit abnormal. 5V_STB and 3.3V_STB are get from +12V by
U3 and UA3. The power supply on standby just provides to Main IC, Key board, IR board, and the
power on signal of Main IC start.

Service manual of MT31AS
The comparison fig of standby power supply
Main IC uses enable control signals such as POWER_ON, LVDS_PWR_EN, BL_EN and MUTE
to control MOS and switch IC to insure Main board work normal. The definition of each enable
signal.
1.POWER_ON：Power supply for start up. And control QA05 and U5 to break off after power on.
Supply power for DDR, FLASH and TUNER.
2.LVDS_PWR_EN：Power supply for panel enables. Control F04 to supply power for OPEN CELL
singly.
3.BL_EN：BL on/off Enable. Control BL driver IC to supply the rise voltage impulse.
4.MUTE：Mute function, control UA1’s work state.
When POWER_ON is in effect, the input of +5V_NOR can be tested from UA01 and UA02.
The +5V_NOR1 can be tested from UK02. 3.3V work voltage is received by TU1, FLASH and UK03.
1.5Vwork voltage is received by U1 and DDR.

Service manual of MT31AS
The comparison fig of power on supply
5.3.2 Small signal process
Decode and I/O part‘s core is main IC (MTK 5531 series chip). IC is used to decoding analog
TV signals such as DVB-T and ATSC code. It supports many kinds of standard video signals, HDMI
1.2a, many kinds of audio format codes, panel driver control, T-CON function, two LVDS,
mini-LVDS generator. Analog video, audio, HDMI signals enter main IC directly. RF signals decoded
to IF signals by Tuner. IF signals are demodulated to parallel digital signals entering main IC by
DVB-T2/T/C decode chip. Analog part signal is inputted to main IC. FLASH storage program and
user data. Main IC read the FLASH’s program when it is work. The key data generated by users
execute operation is also deposited into FLASH. Picture signals are outputted to OPEN CELL by
LVDS. It can generate LVDS or transformed to mini-LVDS by T-con in order to match different
panels. Audio signals are processed to enhancing sound inner main IC. It is transformed to analog
audio small signal outputting to speaker by DAC. Speakers make a processed sound. Audio signals
also generate SPDIF digital signals by coder and are outputted to ports by amplifier.

Service manual of MT31AS
The flow of small signal
5.3.3. Control BUS
HDMI interface includes three groups of differential data, a group of differential clock
transmits media data, and a group of I2C control bus used to EDID and HDCP protocol
communication. When the communication is failure, it may be not able to play FULL HD video.
TUNER transmits the decoded IF signals by IF differential data line. Main IC feedbacks IF-AGC to
control the intension of TUNER’s output signals and uses I2C bus to achieve options such as
channel selection and setting. VGA port includes I2C bus. It is used to UART debug and transcribe
factory data expect EDID communication. FLASH communicates with main IC by SPI BUS. Main IC
needs to communicate with FLASH frequently in power on. IR board receives infrared signal then
Main IC identifies the decoded signals. Key board outputs analog level to Main IC and the signal is
transformed to digital code by ADC to be identified. Main IC controls the BL by BL_ON (BL on/off
enable) and DIMMING (BL intension adjust) signals.

Service manual of MT31AS
The sketch map of control bus
5.4. Module Circuits Test
5.4.1. The audio power amplifier
The IC adopts RICHTEK’s RT9108 chip using 28PIN project. The small sound signals enter IC
after separated. The signals are outputted after power amplifier. Power signals are
connected to speakers LC net. The settings of AMP IC’s peripheries include Gain Control, Power
restrict, Mute control and Abnormal feedback. Mute control is realized by software and
hardware control. Software mute maps to Main IC’s I/O port. Hardware mute is work in AC
cut-off. AMP’s PIN SD will be pulled to low level to mute when power is cut-off for 60ms. C127
will be charged when power is on. And it will discharge though Q101’s E. Because B is power
down, Q101 will break-over. C137 will discharge to Q102’s B and MUTE will be dragged to low.
Then power off mute is realized.

Service manual of MT31AS
The waveform of hardware mute
（CH1：QI01 c pole, CH2：PIN SD)
The Schematic diagram of AMP IC’s peripheries
The Schematic diagram of hardware mute
6. Troubleshooting Flow Chart
These flow charts may not match every single defeat TV set, but they can give you useful
advices when you meet the same defeats described on the titles below.
6.1. Green Power LED does not turn on.
The TV is not work.

Service manual of MT31AS
Many problems may cause the TV can't start up. Firstly，it's need to foreclose the possible bad
board（such as main board, key board, panel etc).We can do the right thing only if we find the bad
board. The main reasons such as: power supply abnormal, core voltage, DDR's reference voltage,
main program abnormal, MBOOT program abnormal, wrong panel parameter, EEPROM data
abnormal, bad Main IC and DDR etc. The print information will be useful to analyzing the
problems quickly recur to the serial interface tools.
6.2. Abnormal display
Check each
DC-DC and there
terminal voltage
regulator unit.
DDR.
Abnormal
Ok
Both have
Check each
DC-DC unit’s
outputs, and the
power supply of
Main IC and DDR.
Check P_ON, DIM,
BL_ON.
Not work
Check 3.3VSTB and
12V/24V
Both
no
Check Power Unit
Only has
3.3VSTB
Check Reset signal of Main IC
Check IIC bus signal. Try to cut off Turner
and AMP bus .Then start up.
Check Crystal
Check print information if necessary.
Check the Main IC’
periphery circuits
and the hole
between Main IC and
peripheral signals.
Change Main IC.
No
Normal
Normal
Normal