Quote:
Originally Posted by frank1492
When the picture has bright white areas (particularly annoying on the news networks when there are constant banners at the bottom of the screen) there is an annoying background buzz/hum, as though there is video leaking into the audio or the signal overloads the set.
Frank
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What usually happens to cause that is the picture carrier getting cut off in the IF amp during the bright white parts of the video. White in TV RF is at minimum video RF carrier, and if biasing in a stage in the IF amp is off, all signal disapears for the time it takes to raster scan thru the white areas. And the sound IF loses the sound signal, as the intercarrier system depends on the picture carrier being there all the time. And when that happens you get noise spikes in the sound. It sounds like a 60Hz buzz as the video raster scans in the vertical dimension repeadly at about 60Hz. So look in the video IF strip for a weak tube, or a bias problem. The AGC might be too agressive, if say on of 3 tubes in the IF is weak.