Yellow tinge in RPTV. Help?

Discussion in 'Displays' started by Mark Shannon, Jul 18, 2005.

  1. Mark Shannon

    Mark Shannon Screenwriter

    Joined:
    May 27, 2002
    Messages:
    1,991
    Likes Received:
    0
    Trophy Points:
    0
    Just today I was watching my television, and the weirdest thing happened.

    Suddenly, the TV flased a yellow screen a couple of times, and went back to normal. A couple of minutes later, the entire screen accquired a yellow tinge, and has since remained unchanged. It was not the channel I was watching, as all other channels do this. As well, the xbox (which is connected to a different input) as well as the DVD player (yet another input) are all experiencing the same phenomenon.

    At first I thought one of the CRT's inside the TV had blown, but I tried to do an auto convergence using the TV's menu, and all three colours displayed perfectly during the auto convergence.

    Does anyone know what happened, and what i can do to solve this?

    PS, the TV is an RCA DP150.

    Thank you.
     
  2. Mark Shannon

    Mark Shannon Screenwriter

    Joined:
    May 27, 2002
    Messages:
    1,991
    Likes Received:
    0
    Trophy Points:
    0
    Anyone? Please?
     
  3. ChristopherDAC

    ChristopherDAC Producer

    Joined:
    Feb 18, 2004
    Messages:
    3,729
    Likes Received:
    0
    Trophy Points:
    0
    This sounds like an intermittent somewhere. You say that the colours displayed perfectly during the convergence sequence. This is, of course, generated internally, so my first thought would be that there is a problem with the input somewhere.
    I assume that you have the video-game system and the DVD player hooked up to the component inputs; are you using an external TV tuner, also connected to a component input? If so, I would suspect the following: there is bound to be an input switcher/buffer amplifier immediately following the component inputs; if the B-Y (Pb) gain were to change suddenly I would expect a shift along the yellow-blue axis. To test this, you could try a Composite or S-Video input, and see if you get the same results.
    In an ordinary TV with these symptoms, I would tend to suspect a bad circuit, probably a component opened, shorted, or changed in value, immediately after the B or B-Y output of the NTSC chroma decoder, but this does not seem to be your problem. At the same time, since the test pattern generator gives a good picture, the driver amplifier for the B CRT is good. [Simultaneous drift in the two R and G circuits would have the same effect, but it would be very unlikely.] Does any of this help?
     
  4. Mark Shannon

    Mark Shannon Screenwriter

    Joined:
    May 27, 2002
    Messages:
    1,991
    Likes Received:
    0
    Trophy Points:
    0
    Thanks Chris.

    Well you were right that I have the game system and DVD player hooked up to the component inputs (each on a different input on the reciever, with one input going into the TV). I am using an external TV tuner, but it however is connected to the TV via a coaxial cable. As such, I doubt it's the reciever gone bad, because the cable tv, which is not connected to the reciever in any way, is experiencing the same thing.

    Ugh, I just don't need this right now. I can't afford a new TV!

    Thanks for the help. Any other input would be appreciated.
     
  5. Mark Shannon

    Mark Shannon Screenwriter

    Joined:
    May 27, 2002
    Messages:
    1,991
    Likes Received:
    0
    Trophy Points:
    0
    Guys I still need some help with this, so if anyone else could help me I'd really apreciate it.
     
  6. Parker Clack

    Parker Clack Schizophrenic Man
    Moderator

    Joined:
    Jun 30, 1997
    Messages:
    12,220
    Likes Received:
    75
    Trophy Points:
    9,110
    Location:
    Kansas City, MO
    Real Name:
    Parker
    Mark:

    Can you plug your DVD player and then the X Box into the back of your set without going through the receiver and still come up with the same problem?

    I would say that if you have the same problem as before that something is amiss with the input circuits of your TV and you will probably have to take the set in (or have someone come out) to check it out.

    Parker
     
  7. ChristopherDAC

    ChristopherDAC Producer

    Joined:
    Feb 18, 2004
    Messages:
    3,729
    Likes Received:
    0
    Trophy Points:
    0
    There are certain assumptions made in the following, which I think are justified: the "yellow tint" is really an absence or strongly reduced level of blue, uniform over the whole screen, so that colour rendition appears unnatural, with purples red, browns orange, and so on; and the "yellow tint" appears with material presented to any input, but colour rendition of internally-generated test patterns is natural.

    The more I think about it, the more I'm sure what the problem is. The only place that a colour fault could occur which would affect both the component inputs and the tuner, without touching internally-generated test patterns, is the "colour matrix" circuit. This is the place where the YPrPb signals from the NTSC decoder [which handles tuner, S-video, and composite] and the component inputs come together and are mixed to produce RGB drive signals for the colour guns. Your test patterns are generated in the RGB domain, downstream of this fault, and so are not affected.
    The worst it could be is a crack in the printed circuit board. This is fixable, but it's hell to find and repair. Better, but still bad, would be the matrix circuit itself, which is almost undoubtedly an IC -- in fact probably part of a larger IC. The good news is that neither of these is very likely. What is likely is that a diode, or a transistor, or one of the bias resistors hanging of the IC has turned, and finding and replacing that [assuming there's not something else upstream which caused it to fail] is a relatively simple and short operation. Depending how the rates in Toronto run, it'll probably cost you a couple of hundred Canadian dollars for the service call, less if you can take it in to the shop yourself. Unless you're trained in electronics and have the proper test equipment, though, I wouldn't suggest trying to do it yourself -- you run the risk of damaging your equipment and you could recieve burns, a dangerous electrical shock, or worse.
     

Share This Page