Friday, August 28, 2015

SONY KDL 40BX420 - KDL 40BX421 TROUBLE SHOOTING CIRCUIT DESCRIPTION AND DISASSEMBLING

SONY KDL 40BX420 - KDL 40BX421 


TROUBLE SHOOTING CIRCUIT DESCRIPTION AND DISASSEMBLING 

CIRCUIT DESCRIPTION
A BOARD
Common to all models utilizing the AZ2-UK chassis, 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.
TUNER
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).
MT5388 PROCESSOR
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.
POWER SUPPLY
There are 3 different power supply boards used in the models in this manual. The type of board depends on the size of LCD panel. They are:
G13 for the 32” models
G14 for the 40” models
G3 for the 46’ models
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.
INVERTER
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.
SWITCH UNIT
This board contains the power, channel and volume up/down and menu buttons.
H BOARD
The power, standby and timer LED’s are located on this board along with the IR remote receiver and light sensor.
TROUBLESHOOTING
Most troubleshooting for this chassis focuses on the 3 major components used:
• The Main Board (A)
• Power Supply
• LCD Panel
This chapter provides practical troubleshooting procedures based on the various symptoms that will appear when a particular circuit fails to operate properly.
VIDEO FAILURES
Problems that develop in the video circuits can appear as subtle or major distortions, a loss of one or more colors, improper video level, or a complete loss of video. When troubleshooting LCD display devices the problem must be isolated to 2 major components: The main board where the video processing is performed or the LCD panel. In some cases the TCON may not be available as a separate component and replacement of the LCD panel is required to rectify a TCON problem.
Distortion in the video signal that affects all inputs can be challenging at times since any of the above mentioned components can be the cause. Fortunately, each of these components tends to generate unique symptoms when a problem occurs. Some distortions may occur that could be caused by either of these components but a good understanding of the circuits and further investigation will isolate the suspected circuit. The following sections will cover the various scenarios of problems that may occur in the video processing circuits.
NO VIDEO
A “no video” complaint can be caused by a number of reasons. The first step is to determine if the condition is present from all input sources. If any video source is working properly, the TCON (located within the LCD panel) can be assumed to be OK. The backlights are also functioning properly. Although it is unusual for a backlight failure to cause a complete loss of video (the TV will shut down if a backlight power or open LED is detected) there have been cases where the backlights have failed to turn on without the unit shutting down.
If the loss of video occurs on all inputs, the problem will require additional diagnostic work. The presence of audio is an important sign to check for. Missing audio accompanying a loss of video helps to eliminate the TCON as the cause and would point to the main board as the culprit. If audio is present, the next step is to determine if the video loss is occurring in the video process circuits on the main board, or the LVDS cable link from the main board to the LCD panel.
Service Tip: If a service call is made for a “no video” complaint, a warranty repair would require the technician to bring the main board to the location. Install the main board and if the video problem is not resloved it is safe to assume the problem might reside in the TCON. If the TCON is not available as a replacement part, this issue would require replacing the LCD panel.
HINT:
One method to test a TCON, which works rather well in most cases, is to remove the LVDS connector at the panel connection while the TV is running. Be certain to release the lock tabs and handle the connector carefully to avoid damage. If there is any tape securing the cable to the panel near the input, temporarily remove the tape to allow free movement of the cable. Carefully insert and remove the connector while slightly rocking it. Observe the screen as you do this. If any activity appears on the screen (flashes, lines or patterns) The TCON is OK. The TV may shut down within a 10 to 20 second period because the protect circuits have detected a TCON failure. If this happens, simply re-insert the LVDS connector, turn the TV back on, and try the procedure again. Normally, you should be able to detect something on the screen within a matter of seconds.
VIDEO DISTORTION
This is, perhaps, the more difficult failure to diagnose. It is difficult when talking to the customer on the phone because an accurate description of the problem must be obtained in order to determine which part (or parts) to bring to the location. It may also be difficult for the technician when the problem is witnessed. If the problem is specific to one or more inputs it should be easy to determine if the fault lies on the main board or a device that is plugged into it. If the distortion occurs at all inputs it must be analyzed based on what appears on the display and isolated to the main board, TCON, or LCD panel. These components usually cause distortions that are unique to the specific circuit. Below is an example of the typical distortions:
Main Board (A Board)
Since the video signal is processed on a frame-by-frame basis it is very unlikely that a distortion that is occurring on a specific part of the display panel is originating here. Distortion problems originating in the video process circuits tend to affect the entire picture. The following are some examples:
• Improper color reproduction or no color
• Improper luminance levels
• Lack of detail in the picture
• Distortions that change with movement in the video
• Diagonal lines
• No video
TCON:
 Since the TCON allocates the RGB video information based on specific timing information, the distortions tend to be fixed and usually appears as symmetrical patterns that occupy most (or a significant portion) of the display. The TCON circuits in this chassis are integrated within the LCD panel which requires replacement of the entire panel to remedy a TCON failure. Some examples of TCON errors:
• No video
• Thin vertical lines spanning most or all of the display
• More that one column of wide vertical columns which may
appear black or any color, or may contain distorted video.
• Multi-colored vertical line patterns with a repetitive pattern
Service Tip:
Whenever vertical lines of distortion appear, select an inactive input or disconnect the antenna in the tuner mode. The idea is to not have a high-definition signal as the source. This allows the picture zoom functions to operate. Change the zoom mode from the remote commander. If the lines follow the normal and zoom modes the problem resides on the main board. If the lines remain fixed throughout the various zoom modes the TCON is at fault.
LCD Panel:
 Distortions originating from the LCD panel tend to be localized with the exception of horizontal line issues. A failure of a gate driver can cause a horizontal distortion with all video content below that point appearing distorted. Depending on which gate driver has failed, the distortion may only cover a small area of the bottom of the screen if the driver failed near the bottom of the panel, or a large area of the screen if the driver failed near the top of the panel. With the exception of visible physical damage, the following are some examples of LCD panel related distortions:
• Any single, thin vertical line (regardless of color)
• Any thin vertical lines isolated to a specific area of the screen
• A singe vertical column of lines of any color or containing distorted video
• Any fixed horizontal lines
• Blotches of black or improperly colored areas
• Ghosting of images in which the entire image is repeated one or more times
A thorough understanding of how the video is processed throughout the chain of circuits all the way to the panel is important. A past article written for the Sony Newsletter described, in detail, how this process works.
AUDIO TROUBLESHOOTING
Since all audio signals are input, processed and amplified by the main board, any issue involving the loss of audio or audio distortions which are present at all inputs would dictate that the issue can be resolved by replacing the main board. It is possible that a software update might also resolve the issue, but it is very unusual for a software update to affect all sources. Once again, always check the Sony Authorized Servicer Portal at SONY WEB for any known and/or listed issues that are software related. Audio problems that are input specific (especially the HDMI and digital sources such as the USB input and tuner) are more likely to point to the need for a software update and this is especially true if the problem is intermittent.
POWER SUPPLY TROUBLESHOOTING
Failures in the power supply circuits that prevent the TV from turning on are caused by one of the following scenarios:
• Complete failure of the standby and main power supplies.
• Failure of the main supply including the main switching regulator, PFC circuit, main relay and other components required to turn the circuits on.
• The power supply is not receiving a turn-on command from the CPU.
COMPLETELY DEAD SET
A complete power supply failure is generally the result of severe transients in the AC line such as those incurred during an electrical storm. This model line utilizes a red standby LED located on the lower left front bezel that is lit whenever the TV is receiving AC power and is turned off. If it is not lit, and AC power to the television is confirmed, replacement of the power supply board should rectify the problem.
TV WON’T POWER ON
This situation assumes that the red standby LED is lit when AC power is applied to the TV. A lit standby LED indicates that the standby power supply is operational, and the CPU on the main board is at least partly operational. In this case it is likely that the main power supply is either not being turned on or it has failed. Use the power-on button on the right side of the TV to attempt a turn-on and eliminate a defective remote control system.
BACKLIGHT ISSUES
Under normal circumstances, any failures in the backlighting system will cause the unit to shut down. If any section of the inverter circuits fails to operate properly, the unit will shut down and blink the standby LED in groups of 6. If one or more of the fluorescent backlights fails to light, the overvoltage protection circuit of the inverter is activated. The inverter shuts down and the same 6-blink protect event occurs. The recommended approach for a 6-blink shutdown is to determine if the backlights are turning on before the shutdown. The easiest way to determine this is to watch for the Sony logo to appear on the screen. The television will make 2 or 3 attempts to achieve proper lighting of the lamps. If the Sony logo appears, the backlights are turning on and the problem is likely due to one of the lamps not lighting. If the lamps never turn on and no Sony logo appears on the screen, the inverter is the likely suspect.
NO BACKLIGHT, NO SHUTDOWN
It is possible for a symptom of no backlighting to occur that does not cause the television to go into protective shutdown. Dynamic dimming control of the backlights is performed by monitoring information from the TCON circuits. This is in the form of data and determines the brightness level of the backlights based on video content. If the TCON fails to process the RGB video data, or if the dimmer data line fails, the backlights will not turn on. Audio will be present if the selected input has it available. The television will remain on indefinitely with the green Power LED lit. In this scenario, the LCD panel must be replaced.
PROTECTION SHUTDOWN
Critical voltages and circuit operations are monitored by the CPU on the main board. If a fault is detected the Self-Diagnostic function in the TV will force the TV to shut down by the CPU. The monitored circuit in which the fault occurred will cause the CPU to flash the Stand-By LED in groups of repeating sequences. The number of blinks in these groups identifies which voltage or circuit caused the] protection event. Not all of the available protect codes are used in every model. For example, models that are LED backlit do not use the 4-blink balancer error as this circuit is found in models that are backlit with fluorescent lamps.
REAR COVER AND SPEAKERS REMOVAL
A. Remove 7 screws from Rear Cover
B. Remove 1 screw from Side Bracket position
C. Remove 1 screw from Terminal Area position
D. Remove 4 screws from Rear Cover
E. Gently lift up Rear Cover from bottom side to detach from Bezel
F. Lift up AC Power Cord and disconnect 1 connector from G14 Board to detach from Under Cover
G. Remove 1 screw from Under Cover
H. Remove 1 screw from Left Speaker Bracket to detach from Bezel
I. Remove 2 screws from Speaker to detach from Left Speaker Bracket
J. Release clips and disconnect 1 connector to detach H Board from LED Guide
K. Remove 1 screw from Right Speaker Brackets to detach from Bezel
L. Remove 2 screws from Speaker to detach from Right Speaker Bracket
M. Lift up Switch Unit and disconnect 1 connector to detach from Bezel.
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