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Toshiba Rear Projection Convergence board problem

Discussion in 'Electronic Repair' started by DogP, Nov 14, 2005.

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  1. DogP

    DogP Guest


    I had a post about a problem with a rear projection 24KHz RGB monitor
    from a Waverunner arcade game (old topic was "50" Mitsubishi Rear
    Projection Help"). Anyway, after looking at it, I noticed that it's
    actually a Toshiba, but I'm unsure of the model (it's missing the back
    panel where the model number should be). I'm starting a new topic as
    the original problem appears to be solved, and this is more of a
    specific problem now.

    I had problems with the monitor not staying on, and it ended up being a
    problem with the convergence board. I found an opened resistor at the
    -15V line on the convergence board, which is a 2 ohm (appears to be a
    1W) resistor. I don't have an exact replacement, but I have lots of
    other low value resistors, which I hooked up to get within the 5%
    allowed of the original resistor.

    Anyway, now it comes up, but the convergence is WAY off. This model
    has no manual pot adjustments, so I guess I have to adjust it all
    through the menu. I do have the remote, but it doesn't seem to be
    allowing me to change any of the convergence manually. It'll let me
    change size and position, but when I follow the instructions for
    adjusting convergence that I found online, it just sits there doing

    You can see a pic of how bad it is here:

    and a picture of the convergence board here:

    and a picture of the chassis here:

    I also pulled the convergence adjustment pages out of the manual and
    they can be found here: , in case any
    of you guys recognize the adjustment procedure from other Toshibas, and
    have seen a similar problem.

    Does anyone know why when I hit the adjust buttons, nothing happens?
    Would it be something with the new resistor I put in, or would
    something else be blown, or is there some sort of protect switch or
    something? Searching the internet for Toshiba convergence problems
    seems to pull up a lot about the output transistors on the convergence
    board, would that make it unadjustable and way out of adjustment, and
    would it seem possible that all three colors are not adjustable?

    So far, I've tested all large transistors on the convergence board, and
    none are shorted, and I've tested the outputs of the remote, and
    they're good. Any other ideas of what to check?


  2. Skype_man

    Skype_man Guest

    Don't adjust the convergence until you repair the convergence
    circuitry. It will be way out of wack, when you later realize it
    was bad in the first place. Replace the STK...-...convergence
    IC's. The resistor is propably blown again. Also check all the
    low ohmage resistors. After repairing the convergence, you can
    "tweak" it if need be. Sky.
  3. DogP

    DogP Guest

    Thanks, I'll replace those STK ICs... I wasn't sure if it was actually
    not adjusting, or if it was trying to adjust and there was just a
    problem with the board. I did test all of the low ohm resistors, and
    the one I replaced is the only one that was bad... and it hasn't blown
    again yet, but it's also higher wattage than the other was.

  4. Guest

    Hi Pat,

    This is a special 15-24Khz (CGA-EGA) Toshiba Monitor built for Video
    Arcade Games I looked long and hard in our company archives and files
    for the schematics but it looks like Toshiba never gave out copies when
    we purchased these.

    <Start File Notes>
    Toshiba 50" Rear Projector Engine Model No:p-R502L

    HOZ/FLY PB6105
    CONV-OUT PB6112-1
    POWER PB6106

    IC Information
    Sanyo STK392-020 3-channel convergence correction amplifier (2pcs per

    To enter convergence mode.

    Note: You need to have a working Game Raster input first

    1/- Switch front panel convergence switch to on

    2/- Press and hold TEST button for 5 seconds until convergence screen

    3/- MODE switches between
    - Center Convergence
    - Line Convergence
    - Point Convergence

    4/- the four POSITION keys select what to adjust in Line & Point
    Convergence Modes

    5/- the four ADJUST keys will move the current selected Convergence

    6/- the three keys R, G & B select and toggle on/off each color

    7/- SELECT will switch between Game Raster input and Convergence Test

    8/- NEVER-EVER press the RESET key.. all stored convergence data will
    deleted from memory and you will have a horrible time just to get the
    screen all squared up again.

    9/- The WRITING key writes the current convergence data to memory. Do
    this often as any power glitch can exit you from convergence mode and
    you will loose all current settings you have made.

    Convergence Tips

    1/- Use Green as your base color.

    2/- Square up the green grid

    3/- use the point convergence to make all the vertical and horizontal
    lines straight as possible.

    4/- For Red & Blue, first use Center convergence to converge the center

    of the screen, Red-to-Green & Blue-to-Green.

    5/- Then Square up each color to match the green, Red-to-Green &

    6/- Finally use Point Convergence to get best overall convergence, Red-
    to-Green & Blue-to-Green.

    <End File Notes>

    Your photos look like all the convergence data has be reset or lost so
    you have a long job in front of you. I don't think that the convergence
    amps are bad as all three guns are giving similar shaped pictures. Bad
    Convergence amps usually show up as one or two colors badly or unevenly

    I start with Green only and use black electrical tape across the
    front evenly spaced to the number of vertical and horizontal grid
    Start with the horizontal first then the vertical. Once you have a good
    green square grid, then adjust the other colors to match.

  5. DogP

    DogP Guest


    Thanks a lot, that helps a TON! I pulled the board out to check for
    the STK ICs, and I noticed that there aren't any on this board (it's
    all discrete transistors). So just for fun, I started testing the
    resistors again, and I noticed that the resistor I pulled was supposed
    to be a 0.2 ohm, and I replaced it with a 2 ohm >_<. I must have put a
    decimal point in the wrong place or something... I always mess up some
    mundane detail ;-). Anyway, I did have an extra 0.2 ohm resistor from
    another arcade monitor, so I popped that in, and it looked a LOT
    better, and best of all, it's adjustable!

    Of course Sky was right, all of the "adjustments" that I was trying to
    make when it wouldn't adjust were saved, and those needed to be
    adjusted back, and tonight I'll take your advice on getting the
    convergence looking perfect, and then hopefully this thing will be
    looking and playing great! :)

    Thanks again for all the help guys!

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