Sony KDL-55BX520 Service Manual ▷ View online
KDL-55BX520 24
SECTION 4 - TROUBLESHOOTING
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
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
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.
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.
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 Flowchart” on page 33
should provide assistance
in isolating the cause of the video loss.
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
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
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
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SECTION 4 - TROUBLESHOOTING
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
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
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.
“Video Distortion Flowchart” on page 33
will assist in isolating
which component is causing the distortion.
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
www.sony.com/asp
for any
known and/or listed issues that are software related.
Audio problems that are input specific (especially the HDMI and
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.
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SECTION 4 - TROUBLESHOOTING
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.
“No Video Flowchart” on page
32
will assist in isolating the power problem.
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 over-
If one or more of the fluorescent backlights fails to light, the over-
voltage 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
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
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.
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SECTION 4 - TROUBLESHOOTING
PROTECTION SHUTDOWN
Self Diagnosis
Supported model
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
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. The following list contains the protect circuits and diagnostics
codes used in the models listed in this manual.
“Protection Shutdown
Flowchart” on page 35
provides guidance in locating the possible
component causing the shutdown.
STANDBY LED FLASH COUNT
FIGURE 4-1. LED DISPLAY
2 times
5 times
LED ON 0.3 sec.
LED OFF 0.3 sec.
LED OFF 0.3 sec.
LED OFF
3 sec.
FIGURE 4-2. BLINK COUNT
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