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KDL-55BX520 16

Always check the Sony Authorized Servicer Portal at 

www.sony.

com/asp

 site for any known and/or listed issues that are software 

related. Most symptoms that are correctable by software updates 

involve communications issues with other devices or minor glitches 

in the operation of a specific function. Below is a list of some of the 

symptoms that may be corrected with a software update:

•  Fluctuations in picture brightness

•  Intermittent picture freezing or noise

•  Problems with certain inputs (especially HDMI)

•  Intermittent or distorted audio

•  Erratic remote control operation

•  Unit turns on and off by itself

•  Loss of color

•  Internet connectivity

•  Certain features not working correctly  

(photo or video file viewing)

KDL-55BX520 17

The primary circuits contained in this chassis consists of a Main Board (designated as the A board), Frame Rate Converter (FRC Board), Power 

Supply Board (G17 Board), and the LCD panel assembly which includes the (TCON) Board. The remaining boards contain switches and LED’s. 
NOTE: For connector part number information, refer to 

Connectors on page 40

. For Wire Dressing information, refer to 

Wire Dressing on page 42

.

SWITCH

UNIT

TCON

FRC

G17

A

H

KDL-55BX520 18

The 

Figure 3-2. Overall Block Diagram on page 20

 provides 

an overview of the AZ2-UK Chassis. Below is a description of the 

components and their functions.

Common to all models utilizing the AZ2-UK Chassis, the Main Board, 

designated as the A Board, contains most of the video processing 

circuitry along with all audio processing. Control of the television is 

accomplished via a CPU embedded within the MT5388 processor. 

Below is a list of the key components located on the A Board.

The tuner is a combination ATSC/NTSC unit. It can receive traditional 

analog NTSC signals via cable or terrestrial along with ATSC digital 

signals via terrestrial (8VSB) or cable (64 or 256 QAM).

IC U3 performs the majority of the necessary audio and video 

processing on the A Board.
Analog Video Input Switch: All analog video sources are selected 

and A/D converted and scaled (if necessary) to 1280 X 720p 60HZ 

resolution.
Digital Audio and Video Decoder: The MPEG2 and Digital Dolby 

audio streams are received from the tuner for decompression. All 

video sources which are not native 1280 X 720p 60HZ are scaled to 

this resolution. Digital audio content is output to the class D amplifier 

for processing and amplification.

Audio Processing: Analog audio sources are selected and A/D 

converted directly by U3. The audio information is then processed 

digitally. Digital audio from the tuner and HDMI sources is also input 

and  processed.  Class  D  amplifier  U8  provides  the  drive  for  the 

speakers.
HDMI Input and Switching: The customer can select the HDMI1 or 

HDMI2 input. Each HDMI input contains a dedicated EDI NVM (not 

shown) to provide display information data to any device connected 

via the HDMI inputs.
CPU: The CPU internal to the MT5388 processor controls all aspects 

of the television functions. Input from the user along with monitoring 

of critical circuits is also performed by this CPU.
LVDS Transmitter: Integrated into U3 is a Low Voltage Differential 

Signaling (LVDS) transmitter. This circuit converts the 8-bit parallel 

RGB video information into a set of high speed serial lines for noise-

free transmission to the TCON circuits located internally to the LCD 

Panel.

This board performs the frame-rate conversion from 60HZ exiting the 

Main Board to 120HZ for the TCON Board on the LCD Panel. A single 

LVDS cable transmits the video information from the Main Board to 

the FRC Board. Dual LVDS cables transmit the up-converted signal 

to the LCD Panel TCON.

KDL-55BX520 19

The Power Supply Board for this model is designated as the G17 

Board. 
There are 2 distinct sections on the power supply:
Standby Supply: Continuously operational as long as AC power 

is applied, the standby supply generates 3.3VDC for the circuits 

requiring power while the unit is turned off. An unregulated 15-volt 

line is present to provide power to the main relay, PFC and main 

power supply at turn-on.
Main Supply: Once the power supply receives a power-on command 

from the CPU on the A Board, the main switching supply is turned 

on to provide a regulated 12V source, a dedicated un-regulated 15V 

for the audio circuits and an unregulated 24V source for the inverter 

circuit.

The inverter receives the unregulated 24V from the power supply 

board and generates the required high voltage AC to power the 

backlight lamps. A control line to turn on the inverter (backlights on) 

is used in conjunction with a dimmer control to vary the light level of 

the CCFL lamps.
As of the writing of this manual, the inverter is not available as a 

replacement part. The LCD Panel Assembly must be replaced.

This board contains the power, channel and volume up/down and 

menu buttons.

The power, standby and timer LED’s are located on this board along 

with the IR Remote Receiver and light sensor.