Mag xj770 too bright

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Hello.

What you are reporting is a problem in the color driver section of your CRT monitor. Usually this is from a failure of the blue driver to the CRT Blue gun. The blue driver controls the amount of conduction through the blue electron gun in the CRT.
If the driver fails, the default result is full conduction of the blue gun circuit which will overdrive everything else on the screen and will make the retrace lines visible.

I do not know your level of experience if any, so I suggest you consult your local repair shop for an estimate. Now that you are armed with knowledge of the problems origin, you should be able to get a fair estimate. If it was working and just went blue, either the driver transistor broke down, or one of the components that create the controlling bias for the blue driver circuit has failed. If your level of experience is such that you are going to attempt a DIY, be mindful of the high voltage at the CRT flyback transformer lead. (40KVA). I won’t kill you, but you will probably hurt yourself trying to pull away from its bite.

If you opt to not repair it, new 17 inch LCD flat panel monitors can usually be purchased for around $150 or so.

Only you can decide which choice is right for you. At least now you have a few facts to help make the decision.

I hope this helps.