If the monitor is defocussed, then there is probably not much you can do. The tube focus is determined by the voltages on the tube electrodes, and if one of these is wrong, then it would need the attention of a skilled repairer to fix it. A common cause of defocus is when the tube cathode emission is low and the user turns up the brightness and contrast controls to get a useable picture. The circuits can't supply the extra electrode current and the voltages fall, resulting in the defocus.
I would expect the minimum cost of a repair to be of the order of £50, and you can get a very good 17inch CTX monitor for £79.66 inc VAT (£86.47 including delivery)click here
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