Sony KDL-32BX320 / KDL-32BX321 / KDL-32BX420 / KDL-32BX421 / KDL-40BX420 / KDL-40BX421 / KDL-46BX420 / KDL-46BX421 Service Manual ▷ View online
KDL-32BX320/32BX321/32BX420/32BX421/40BX420/40BX421/46BX420/46BX421 20
SECTION 3 - CHASSIS OVERVIEW
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
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.
KDL-32BX320/32BX321/32BX420/32BX421/40BX420/40BX421/46BX420/46BX421 21
SECTION 3 - CHASSIS OVERVIEW
COMPOSITE OR
COMPONENT 1
RF
COMPONENT 2
HDMI 1
PC HD15
POWER SUPPLY
SWITCH
UNIT
LED
IR RX
LIGHT
SENSOR
LCD PANEL
A
G13 (32")
H
L
R
ANALOG AUDIO OUT
OPTICAL AUDIO OUT
U3
MT5388
A/V DECODER
A/V PROCESS
CPU
TUNER
USB2.0
HDMI 2
LVDS
24V B+
AND CTL
AC IN
INVERTER
U8
CLASS D
AUDIO
AMP
G14 (40")
G3 (46")
*HDMI 3
*BX421 MODELS
ONLY
IC4305
TEMP
SENSE
FIGURE 3-3. BLOCK DIAGRAM
KDL-32BX320/32BX321/32BX420/32BX421/40BX420/40BX421/46BX420/46BX421 22
OVERVIEW
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. Typical failure symptoms will be discussed
in this chapater with troubleshooting flowcharts for each symptom in
the
Section 5 - Flow Charts and Diagrams on page 31
.
NOTE: Always remember to check the Sony Authorized Servicer
Portal at
www.sony.com/asp
to access the latest technical bulletins
along with triage charts to quickly identify the most like part to
complete the repair based on the symptom.
UPDATING THE SOFTWARE
As mentioned in
Section 2 - Software Requirements
, there are
several issues that may be resloved by updating the software to the
latest version. For a list of possible correctable issues see
Checking
the Software Version on page 15
.
SECTION 4 - TROUBLESHOOTING
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
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.
KDL-32BX320/32BX321/32BX420/32BX421/40BX420/40BX421/46BX420/46BX421 23
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. 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.
Figure 5-2. Video Distortion Flowchart on page 32
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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