On the chassis there is a round coil called the horizontal width coil. The diameter is maybe the size of a nickel, with a hollow center that has a threaded screw, which requires a special allen/hex driver to adjust. DO NOT use a metal tool to adjust this with the unit on or you will toast your fingers fast, and may cause damage to your moniter. The special PLASTIC adjusting tools can be found online from various electronic suppliers. Also, I recommend letting your moniter powered on for an hour or so to warm things up, the adjusting screw is plastic and extreme care should be given in your attempt to adjust as the coil and screw become fragile from age and the heat its been exposed to. Dont force it, if your not able to adjust it, you'll need to find a new coil.