Complete Loss Of Video; Heartbeat Led Indicators; Fbu Board - Sony KDL70XBR7 Training Manual

Troubleshooting
The circuits for processing the video signals are located on 3 circuit boards.
The AU board is responsible for selecting the various analog inputs. The
FBU board processes both digital and analog signals resulting in an image
that is always 1920 X 1080p with a 60HZ refresh rate to be sent to the
CF1 board where it is up-scaled to a refresh rate of 120HZ. At this point it
enters the TCON board on the LCD panel.
Video failure complaints are the most difficult to troubleshoot (especially
when attempting to analyze the problem over the phone with the customer).
The symptoms can occur as a complete loss of video, missing sections
of video or distortions in the picture. One of the first steps is to try and
determine if the problem is input specific or involves all signal sources.

Complete Loss of Video

The presence of audio is important in determining whether the complaint
of "no video" is valid. Having the luxury of active audio is not always
available since the unit must be set to an active input with a known valid
audio source. Several circuits can cause this condition.
• No backlighting
TCON failure
•
• CF1 board failure
• FBU board failure
• AU board failure
It is not likely that a backlight failure in this chassis will be the cause of a
no video complaint. If the backlights fail to come on the unit will shut down
with a diagnostics failure (usually a 6-blink inverter error). There are cases
where units have been found to be running with no backlights (audio was
present) and no shutdown occurs. The last step of the microprocessor
initialization routine is to turn on the backlights. If a problem occurs during
the initialization routine and the backlights are not turned on, the CPU is
unable to continue on to the protection monitoring stage. In these cases
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Chapter 2 - Video Circuit Troubleshooting
replacement of the FBU board is necessary.
If the TCON fails completely the usual result is a loss of communication
between the TCON and the FBU board and the unit will shut down with
a 5-blink PANEL ALERT indication. The CF1 board can also cause a 5
blink error to be generated since the TCON communications data must
pass through it. The cause of a 5 blink error is easy to distinguish. If the
communications line fails because of the TCON board or LVDS cable the
shutdown will occur within 5 seconds. If it is caused by the CF1 board
(assuming there is no physical de-coupling of the data line between the
TCON and CF1) the television will run for approximately 1 minute and 20
seconds before the shutdown occurs.
The presence of on-screen display graphics is a clear indicator that the
TCON and LCD panel circuits are functioning properly. If the video failure
affects all input sources but OSD is present, the FBU board is the cause.

Heartbeat LED Indicators

The AMD processor located on the FBU board and the frame-rate
doubling circuits on the CF1 board contain "heartbeat" LED's which can
be very helpful when troubleshooting a "no video" condition. Although the
presence of a blinking heartbeat LED does not necessarily eliminate the
possibility of a failure in that particular circuit, a continuously lit LED or
one that does not light at all clearly indicates a problem on that particular
circuit board and replacement of that board will remedy the failure.

FBU Board

The heartbeat LED on the FBU board is located at the top right corner. It is
visible through the holes on the shield as shown in Figure 2-2. If a failure
occurs in the AMD processor this LED is usually lit steady green and this
is the most common symptom. There have been cases of the LED not
lighting at all. This indicates a failure of the regulator circuit on the FBU
board supplying B+ to the AMD processor.
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