My 15-inch Mag CRT monitor (model D510) first started its symptoms with an intermittent loss of vertical sweep (single horizontal line across the screen) for only a second or two, then return to normal. Days later, new symptoms appeared: the picture would shrink to 2/3 of its original size, be off-center, and come with a decrease in brightness. At other times, the picture width and height change intermittently. Actually, it's as if the monitor is changing resolution settings at random. Sometimes it would return to normal, sometimes it wouldn't. Although there is still good synchronization and the picture is still intact, it's getting such that I can't do much work with it. I suspected it's the jungle IC - STV7778. I replaced this 42 pin jobber and this cured the decreased brightness problem. But the picture problem is still there. I can use the horiz and vert size controls to bring the shrunken picture to fill the whole screen again, but in a few seconds, the picture becomes too wide and I'd have to readjust the size controls again. I know it's not the computer's video card because connecting another monitor there doesn't show these problems.
I have a dual trace 100 MHz oscilloscope and know how to use it. How can I use it to pinpoint the problem? Also, I'm beginning to suspect the microprocessor IC. What do you guys think?
I have a dual trace 100 MHz oscilloscope and know how to use it. How can I use it to pinpoint the problem? Also, I'm beginning to suspect the microprocessor IC. What do you guys think?
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