Does the line come up every time you power on? Look for bad solder in the vertical output circuit. A diode off of pin 6 to pin 3 may be the problem, if not the IC. Diode may seem good on checks in the circuit, but bad out. With the set on the voltage at pin 3 should be slightly higher than pin 7. If you are not a technician then I would not suggest trying to fix this on your own.