Sony KDS-R50XBR1 Training Manual page 100

If there is no audio present at the Audio Output Var/Fix jack then the
problem exists in the audio switching circuits located on the ASU-Board.
Replace the ASU/DSU Assembly to repair problem.
If there is audio present at the Audio Output Var/Fix then the audio switching
circuits are OK and the problem is located in the audio processing circuits
located on the AK-Board or K-Board. Before replacing either the AK-
Board or the K-Board follow the next three steps in the troubleshooting
flowchart to confirm the power supply voltages for each board. These
steps will determine if the cause of a missing or distorted audio output is a
missing or insufficient power supply voltage.
The power supply voltages are accessible on either the ASU-Board
(3.3V and 6.5V) or the G-board (14V).
directly on the AK-Board and K-Board, however, the C-Board cables
must be disconnected and the complete chassis assembly partially
pulled out. In the case, the unit will go into protection mode after turning
ON. Consequently, the voltages must be check prior to the unit shutting
down.
You will first check the 3.3V and 6.5V power supply voltages to the AK-
Board. The 3.3V powers both the AK-Board and the K-Board. The 3.3V
is fed to the K-Board through an inter-AK-K board connector.
Power Supply voltage
ASU-Board CN1/pin 10
Power Supply voltage at
ASU-Board CN501/pin 1
If either the 3.3V or 6.5V are missing then the problem exists in the power
TVP-21
Check
Audio Output
Var/Fix
The voltages can be check
Check
at
(3.3V)
Check
(6.5V)
supply circuits. Replace the G-Board.
If both the 3.3V and 6.5V are OK, then the next step is to check the 14V
power supply voltage directly connected to the K-Board. The 14V powers
the digital output amplifier circuits.
Power Supply voltage at
G-Board CN6408/pin 1
IMPORTANT: To access the CN6408 when checking the 14V power
supply voltage you must partially pull out the complete chassis assembly.
Consequently, the C-Board cables must be disconnected. The unit will
go into protection mode when turned ON. Therefore, place your meter on
CN6408/pin 1 before pressing the ON button to check for the presence of
14V before unit shuts down.
If the 14V is missing then the problem exists in the power supply circuits.
Replace the G-Board.
If all the power supply voltages (3.3V, 6.5V, and 14V) are present and at
the designated level then the final check before replacing either the AK-
Board or K-Board is the speaker system.
Speaker Resistance &
Connections on K-Board
The speakers should measure 10.6 ohms each. Measure the speaker
resistance at CN3003/pins 1, 2, 3, 4. Confirm all speaker connections to
the K-Board are secure and undamaged. Replace or repair the system if
necessary.
If the speaker system checks OK, then the problem exists on AK-Board
or the K-Board. Because both boards are located underneath a shield
it is difficult to make any measurements to isolate the problem to either
board. Therefore, the easiest way to determine which board is defective
is through know good board substitution. Install the AK-Board and K-
Board individually and test unit for proper audio.
6. Audio Processing System
Check
Check
97