22
6. RA-3/3A Video Process Troubleshooting: T & S Models
With AKB and high voltage ruled out, the following tests can be performed:
The OSD feature is the first tool. Press the menu button on the remote. If you do not have a remote, press
channel up or down. The idea is to get the main CPU to generate OSD graphics. If no OSD appears, the Y/C
Jungle IC206 is suspect at this point since OSD has its own path directly into it and it is highly unlikely that both
the OSD and IC206 have simultaneously failed. Anything is possible, so several more checks are necessary
before making the decision to change IC206. If OSD is present, the next test will be even more important.
Using the remote, engage the PIP feature. If a small box appears (whether or not it has video in it), you can be
reasonably certain that the sub video path is OK. This also verifies that the lack of video is not being caused by
the YM input at IC206/pin 12 or the YUVSW input at pin 5. The YM controls the luminance level when the
customer menu is displayed. It lowers the video level so the menu stands out from the background video. This
line is normally low and if it is pulled high, all video inside IC206 will blank. The YUVSW is a line that switches the
video off behind the PIP box since IC206 does the mixing of main and PIP internally. This line is also normally
low and if pulled high, it will kill the video. Both signals can cause this problem and they guarantee an unnecessary
Y/C Jungle replacement by the technician.
Assuming the PIP will appear along with the OSD, the main video path is where the problem lies. Try getting
active video in the PIP box (if you don’t have it already) and see if you can change the input source to the PIP.
This helps to verify that the A/V switch, IC1101, is probably OK. From here, it becomes a signal tracing chore. If
no video is present with an S source, the comb filter is OK. The YC from this source bypasses the comb filter. If
S video is present, troubleshoot the comb filter, IC1702. Watch for distortion or loss of the FSC signal at pin 11
of IC1702.
Video Level or Distortion Problems
Distortion in the video signal can be quite troublesome. This is especially true if the distortion is subtle since you
may not be able to see it on the oscilloscope screen. The T and S line models do not digitize the video like the
higher end units, so distortion tends to be caused by either power supply noise or the Y/C Jungle IC. Video level
problems can happen virtually anywhere.
Distorted Video: Isolating the source of distortion by utilizing some of the video features in the set (the same way
described previously for a “no video” condition) is the best way to localize the cause. The rule-of-thumb for video
distortion diagnosis depends on whether or not the distortion is synced with the picture. If it “floats” or moves
around, it is likely coming from an outside source such as power supply or a radiating component. If it is either
stationary or completely random, it is occurring in the video processing circuits.
Once again, using the OSD is the best way to get an overall idea of where to go. If OSD is not distorted, it is an
excellent indication that the RGB drive path from IC206 is good all the way to the CRT. It also indicates that
IC206 is probably working correctly, although it has not been eliminated as a problem yet. If the customer menu
exhibits the same distortion, you will have to work from IC206 forward to the CRT drive circuits. Since the signal
is now split into RGB components, it is a given that IC206, B+ sources and the CRT itself could be the cause.
If OSD is clean, the next step is to engage PIP and see what the child picture looks like. If it also suffers from the
same distortion, there is a possibility of power supply noise and IC206 becomes a suspect. The main and sub
video paths enter IC206 at different inputs. Other than power supply noise, it is unlikely that both paths have the
same failure causing the distortion. Check the 5V, 9V and 12V supplies for ripple. If the B+ lines are clean, the
next step would be to check IC206.
Another useful tool is to apply a component signal to the video 4 input. By looking at the block diagram in figure
6-1, you can see how this signal path bypasses almost all of the process circuitry.
Incorrect Video Level: One very important item to remember about the RA-3 chassis is that the AKB circuitry
does not
blank the video when a problem occurs in this circuit. You do have the advantage, however, of seeing
