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Toshiba 32" model 32A10 Television

Discussion in 'Electronic Repair' started by [email protected], Jan 10, 2008.

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  1. Guest

    There is no display of the selected channel, volume level or any menu
    items when menu is selected. I know the tv is in menu mode because
    when menu is pushed, the volume control buttons no longer change the
    volume level but are adjusting something instead. Because there is no
    on screen display, I have no idea what is changing. Any ideas?
     
  2. AJ

    AJ Guest

    Determine what is causing the crt not to produce any raster, i.e. deflection
    or hv problems, then diagnose the video problems, possible when the crt
    produces a raster that the video will be present. Post what actual
    electronic diagnostics have been done inclusive of voltage measurements.
     
  3. Guest

    Sorry, I should have indicated that the picture is fine (ie the
    raster, deflection, and hv is fine). RF input, video 1 or 2 all work
    fine (produces a clear picture). What does not function is the
    digitally generated display of the channel selection, the volume
    level, or any menu item if the menu button is pushed. The video
    picture itself is fine.

    I successfully did the procedure to reset the registers to the factory
    default settings. Now the picture is distorted because the registers
    that set the horz & vert height & position have been defaulted. There
    are several other registers that also need to be adjusted, but I can't
    do it because there is no on-screen display of the selected item.
    Therefore I can't tell what it is I have selected to adjust.

    I purchased and downloaded the service manual. I could email it to you
    if you want to have a peek. I have been trying to determine which chip
    produces the on-screen video and how it gets mixed into the video
    path.

    Bob
     
  4. Guest

    Update:

    Found a block diagram of the Toshiba TMPA8700CPN micro proc (QA01 in
    the schematic). It produces the On Screen Display found in the TV.
    Pins 31 &32 have a 8MHz oscillator attached that is functioning. Pins
    28 & 29 are connected to LB01, a TRF1196D IF Coil. I do not see this
    oscillator functioning. Anyone out there know what the characteristic
    of the TRF1196D coil are? (DC resistance?). Additionally, would anyone
    know what frequency this oscillator is supposed to run at?

    It would be my conclusion that either the TMPA8700CPN micro proc
    (Toshiba part number 23000287) or the TRF1196D IF Coil (Toshiba part
    number 23262280) would be the issue. I have removed both parts and
    cleaned the circuit board to remove any residue that might cause this
    high impedance circuit to malfunction.

    If any of you out there are interested, I have the schematic diagrams,
    etc. and could email them .

    Any help would be appreciated!

    Thanks!

    Bob
     
  5. TOH

    TOH Guest


    Final Update:

    TMPA8700CPN data sheet input output circuitry section revealed that
    the oscillator is gated and that was why it was not observed to be
    working. When a button is depressed, the osc. starts and runs for the
    duration of the display. I observed a frequency of about 1KHz.
    Assuming this was the dot clock for the display, the frequency should
    be at least 8 dots/char X 32 char/scan line X 15,750 scan rate =
    4,032,000Hz. The osc. must actually run faster because of the
    requirement for margins on the left and right sides of the display as
    well as retrace time.

    I once again removed the TRD1196D coil.. Its DC resistance measured
    about 860K. I decided to mechanically open up the part and see what
    was inside. I found that the measured DC resistance was the result of
    pollution inside the part and the coil itself was open. Using my fine
    tip soldering iron and my magnifying lens, I managed to restore the
    connections. DC resistance turns out to be less than 1 ohm.

    The Oscillator now runs at 5.7Mhz and the display works fine. The osc.
    is gated by the horizontal sync signal to avoid jitter.

    Bob
     
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