I have a 32" Toshiba that displays a picture, but the on screen display of the selected channel, volume, or menu item when menu is selected does not appear. I have successfully followed the procedure for initializing the registers in the QA02 processor but still no display. Any ideas?
Bob
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!
Cheers from Canada!
Bob
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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