Sylvania model 6427tf screen off
Hello,
Depends on what exactly you mean by off center, and when it is like this.
If the picture is shifted one direction (usually to the right) or another regardless of the inputs (cable, rca/composite, off air antenna, etc), then you are looking at a timing issue inside the TV itself. Though there may be controls at the back of the tv, inside the enclosure, they generally do not address this particular issue. Red / Green / Blue gun bias, overall brightness, screen, but not timebase correction.
If your picture is shifting with a single input, like when using a digital converter box on the composite input, then you might be able to adjust the picture using the converter box itself (look in advanced menus). This is a simple timing error between the converter and your TV. Try a different converter box as well, yours may be having issues.
Lastly, if the picture appears to be "reduced" so that there is a band around at least 2 sides of the picture, then you might be experiencing a low voltage condition with the outlet associated with the TV. The power supply inside the TV may be failing as well.
Try the converter box first, then a different outlet (on different breaker), then talk to a service shop.