Sony KDP-57XBR2 Training Manual page 108

Video failures fall into three main categories:
1. No video
2. Distorted video
3. Improper level
Although the video signals are routed through many different paths depending on the type of signal being received,
these different pathways can be used to an advantage when diagnosing video failures. The picture & picture
feature provided by the MID circuitry provides a useful diagnostic tool. Since it is able to display two video
signals simultaneously, isolating which stage is causing the problem can be accomplished easily. This feature
will be used extensively in the troubleshooting procedures to follow. Figures 26-2, 26-3 and 26-4 provide more
detailed block diagrams with pin locations and voltages to assist in further isolating where the failure has occurred.
No Video: Two possible causes of this symptom must be ruled out first. There must be high voltage present and
the unit has not encountered an AKB error. Listen for the sound of high voltage and verify it is remaining on by
observing the CRT filaments are still glowing or watch for eight flashes of the timer LED. If the high voltage is not
present, refer to Chapter 25 for troubleshooting methods. AKB errors will be displayed by the timer LED flashing
in sequences of five. AKB troubleshooting will be covered in Chapter 27.
Once high voltage and AKB have been ruled out, try bringing up the customer menu. If it appears, there is a
good chance the video process IC309 is working properly. The purpose of trying to get OSD on the screen is to
eliminate IC309 as a source of the failure. It could still be at fault since active video enters it via a different input.
The picture & picture feature will be used next. One item that is unique to this new feature design is that HDTV
signals from video 5 and 6 can only be displayed in the left box. Video 5 and 6 will only accept component video
sources. NTSC inputs and the two analog tuners will display in either box. If you have a 1080i generator,
virtually all of the video processing circuits can be bypassed to further verify the operation of IC309. If you do not
have a HD generator, using the Twin Picture mode with main and sub tuner video will be adequate. By using this
feature, the main and sub-video paths are displayed together and a wealth of information can be obtained to
isolate the video failure.
Video Appears in Right Box Only: The sub-video path is working correctly. An interruption in the main
video processing path has occurred. In previous designs, this symptom eliminated the DRC circuit since
it was bypassed by sending main video from the decoder directly to the MID. The RA-6 chassis will route
main video through the DRC for normal viewing and the Twin Picture mode. The presence of Y signal will
need to be checked at pin C20 of CN13 on the A board to verify whether the problem lies in the main
analog path on the A board or the digital circuits on the B board.
Video Appears in Both Boxes: The main and sub paths are functioning. The video signal is not being
switched properly and the MID is likely the cause. Replace the B board.
No Video in Either Box: What is very important at this point is whether the screen remains completely
blank. The MID IC3408 generates a gray background with two boxes for the twin video presentation. If
this background information appears and there is no video in the boxes, either a failure of both main and
sub video has occurred or the MID is not processing the two video sources. Check CN13, pin C20 on the
A board for a main Y signal and sub Y at pin A6 to isolate the B board. Verify proper B+ at CN13 on the
A board of 5V at pin A23, 3.3V at A25 and 9V at A27. Replace the B board if present.
If the screen is completely blank and OSD is present, the B board is at fault. Check the voltages mentioned
above before replacing the B board.
Video Level and Distortion Problems: The same procedures used to isolate a "no video" condition can be used
to locate the source of distortion or level problems. 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
26. RA-6 Video Circuit Troubleshooting
105