Sony TV

Hello, and I don't recall seeing any component labeled "light engine" on the schematic diagram of a television receiver ;-). I assume from your posting that you've got a set that uses a CRT (picture tube) as a display. A thin white horizontal line indicates a malfunction in the vertical sweep circuits. It could be a vertical output transistor(s), a short/open in the coil of the vertical deflection yoke or something in the circuits comprising the vertical sweep oscillator. Also, a component may not be defective - a broken/cold solder joint(s) can also be the culprit. Sincerely,

The KDF-E42A10 is an LCD rear-projector. No deflection circuit as such.

I don't think the OP said a thin white line - just "a line".

Could be almost anything. This model has a tendency to develop a red-blue shading at the top and bottom 1" or so because of (probably) a bad polarizing filter. Generally the whole light engine must be replaced because individual parts for the optical engine are not sold.

Mark Z.