The problem you are experiencing is actually pretty common. The likely cause is a faulty capacitor in the vertical circuit. The circuit itself could be bad, but unlikely.
If this is something you are going to try and repair yourself you will need a service manual for your unit. Unless you have some experience with this - I HIGHLY RECOMMEND USING A REPAIR TECHNICIAN - there are extremely dangerous voltages present inside your TV - EVEN WHEN UNPLUGGED. It is not a safe place to mess around with if you aren't very familiar with it.
Capacitors cost less than a dollar each and all you will be out is the repair tech's time (hour or less).
Consult your TV manufacturer to determine if they provide a repair option for faulty capacitors.
Otherwise, if you want to have an idea of what is going on and what it would cost to repair, here you are a link of a technician service
http://1stresponseelectronics.com/, August 2013