If the tube is producing the three colours, red, green & blue, it is likely OK. The electron beams for illuminating each colour are scanned left to right across the screen repeatedly while being deflected from top to bottom many times per second by a varying magnetic field produced by a yoke mounted around the neck of the tube between the screen and the electron "guns" positioned inside. There may be a problem with the vertical deflection circuits; could be something as simple as a bad connection or a fairly inexpensive part gone bad.
Request an estimate and establish a maximum price for the repair with consideration of the value of the set and replacement costs.
The prices of newer T.V.'s are very competitive and digital sets are also coming down. This might be a good time to consider an upgrade.