Sony KDP-57XBR2 Training Manual page 69

14. RA-4A Video Circuit Troubleshooting
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Gray Background Appears With Two Black Boxes: IC511 is OK. This signal is generated by the MID . The main
and sub video paths are not working. Since a failure in both paths at the same time is unlikely, suspect A/V
switch, IC515 or a crack in the board.
Screen Is Still Blank: This leaves IC511 as the likely cause. It is not able to process video from either of the inputs
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from the MID or DRC circuits. IC511 is getting B+ because high voltage is working. There is no need to
check the RGB output path to the CRT boards. Since the unit is not showing AKB problems, the IK pulses are
getting to the CRT's via this path. Check to make the YS/YM line at pin 49 of IC511 is low. This line is used to
switch video off behind PIP boxes and reduce background video when the menu is called up. If it is stuck high,
all video will be blanked.
Troubleshooting Video Distortion and Level Problems
The procedure for localizing the problem is very much the same as locating missing video. The idea is to narrow
down the area in which the problem is present. With the introduction of multiple A/D and D/A converters and
digital processing circuits, noise in the video is likely to be more common and can take on some strange symptoms.
Fortunately, most digital noise problems have a distinct digital appearance. They may be stationary on the
screen or move around in a clock-like stepping motion. Minor or severe loss of picture detail is caused by one or
more of the parallel bit lines being inactive. The more significant the bit, the more detail loss will occur. Power
supply and external noise will "float" since they are not synchronized with the video.
Video level variances are confined to the analog circuits of the set. If all functions are too high or too low, the
video processor is the cause. Watch the ABL line at pin 44 of pin of IC511. It should be around 2.5VDC with a
white screen. A significantly lower voltage indicates a problem in the ABL pull up circuit. Make sure that YS/YM
at pin 49 is not locked at 2.5 to 3VDC. A quick way to eliminate these is to engage the customer menu. Its video
level is not affected by ABL or YS/YM. If is bright as compared to active video, IC511 is probably OK
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