NotTaR of Television Sets : No video on late model Sony TVs         
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No video on late model Sony TVs

(From: David Kuhajda (dkuhajda@locl.net).)

This following assumes that the more basic TV troubleshooting has already been performed and resulted in no solution - i.e., filaments are lit up, CRT voltages are all correct but the cathodes are all in cutoff, main power supply voltages are present, etc

The 3 most common causes of no video, but good audio are as follows:

  1. AKB blanking due to either a fault in the AKB circuit or the CRT has one gun that is too weak and the AKB won't unblank the CRT.

  2. Loss of vertical deflection. The system control must see the vertical return pulse to unblank the video.

  3. Loss of data bus communication with the Jungle IC. The Jungle IC must send the all OK signal to the micro before it will unblank the video.

To troubleshoot:

  1. Try changing the volume with the volume control. If it changes the data bus is not the problem. This is assuming the TV is tuned to a good TV station.

  2. Mark the EXACT position of the screen/G2 control with a marker. Then turn the G2 control up.

The typical failure mode of the vertical circuit in a Sony causes only one of the vertical supply resistors to open usually. Either the +15 V or -15 V. This puts a full + or -15 V on the yoke which deflects the guns into the glass envelope of the tube.

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