1. Herringbone in TV
Disconnect modulator from local channels and check modulated channel. If there is programming move the modulated channel. If the picture is snowy, use a low pass filter to block noise or data coming in from cable.
2. Horizontal Bars Rolling Through TV Picture
2.1. Check for a component of the system that is introducing DC power into the system. Disconnect that component and check TV. If the hum bars stop, use a DC blocker down stream from that component to block the power from getting to the TVs
2.2 If the rolling is only on the modulated channels, check for impedance mismatch by adjusting the video level adjustment pot.
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