Advent TS2766A tv has no picture and a horizontal blue line across the screen

Hello
Only one line across the screen is due to total vertical sweep failure. In all CRT tvs have both vertical and horizontal sweeps to spread the picture to the entire screen. If vertical sweep failure occurs, you will see a horizontal line across the screen, and if horizontal sweep failure happens, you will see a vertical line in the middle of the screen or no lines or a dead tv.
In your TV, now the sound will be ok, I thinks so, and posts this solution.

You just open your tv, and locate the vertical output section in the circuit board. It is very easy to findout. Just see the four wires goes from the deflection yoke [the coil fitted at the neck of the picture tube], there will be four of them, out of which two of them will be thick, usually red and blue coloured, and another two of them will be thin. You just follow the two thin wires, which in turn goes to a plug in adaptor and to the circuit board. Just put the circuit board upside down and follow the two tracks undeneath, which will guide you to the vertical output section.
There you can see an IC screwed onto a metal heatsink. That is the vertical output IC. Just check keenly for any loose solderings on the legs of that Ic. It may happen because, this Ic will heat up when the set works. Prolonged times of heating and cooling may make loose solderings or bad solderings. It is very difficult to locate the exact loose point because some of them may have micro type loose contacts, that can't be detected with naked eye.
You just resolder all the legs of that Ic, by applying a little more solder, without shor circuiting the terminals. Chek whether you have rectified the problem or not. If not check the main supply point leg voltage. If there is no voltage follow the track and find out the fault. If there is voltage, check the voltage at the output pin of that Ic. It must be somewhat half to that of its supply voltage. If main voltage is there, and there is no voltage on the output pin, or that voltage is equal to that of supply voltage, the vertical output IC is defective. Resolder it out from the board and go for a same type and number. Replacing it will solve your problem. There is an other rare chance to get the vertical windings in the deflection yoke to open. Bu it isvery rare, out of 1/1000 of it may happen. It can be checked by continuity measuring of that coins winding ends.
You just go with confidence. Take every precautions we take before working with an electrical equipment. Proceed. You can and you will. Take care. OK.