manen@nvpna1.prl.philips.nl (Rob van Manen) (10/18/90)
Hi, My father's Commodore 64 has quite a strange problem. When the characters on the screen scroll up, the color of the characters changes! When e.g. I list a basic program of just a few lines, and the characters are white on a blue background, the characters stay white. But when I list a longer program, so that the lines scroll off the screen, the color of the characters changes from the white cursor-color to mostly black, though other colors appear also. When you pause the listing, or break it, the color of the characters on the screen remains the same. We thought that perhaps the color-ram was broken, but the fact that the colors stay the same when the screen does not change, indicates that the video processor can read the ram correctly. With a basic test program however, with which we write a value into the color-ram, and read it back again, the value we read back is often not correct. If someone out there could tell us what to do about this annoying problem, we would be very grateful. Thanks, Rob van Manen. Rob van Manen. | email - manen@apolloway.prl.philips.nl or | manen%nvpna1.prl.philips.nl@uunet.uu.nl | SERI - manen:nlwaya01 or MANEN:NVPNASA
scott@max.u.washington.edu (10/20/90)
In article <manen.656196919@nvpna1>, manen@nvpna1.prl.philips.nl (Rob van Manen) writes: > Hi, > > My father's Commodore 64 has quite a strange problem. When the > characters on the screen scroll up, the color of the characters changes! > When e.g. I list a basic program of just a few lines, and the characters > are white on a blue background, the characters stay white. But when I > list a longer program, so that the lines scroll off the screen, the > color of the characters changes from the white cursor-color to mostly > black, though other colors appear also. When you pause the listing, or > break it, the color of the characters on the screen remains the same. > We thought that perhaps the color-ram was broken, but the fact that > the colors stay the same when the screen does not change, indicates that > the video processor can read the ram correctly. With a basic test > program however, with which we write a value into the color-ram, and > read it back again, the value we read back is often not correct. > > If someone out there could tell us what to do about this > annoying problem, we would be very grateful. > > Thanks, Sounds like a classic case of the power supply going faulty. Try borrowing a working power supply for the C64 from a friend and see if that fixes it. Sincerely, Scott K. Stephen
rickc@pogo.WV.TEK.COM (Rick Clements) (10/23/90)
In article <14474.271f60da@max.u.washington.edu> scott@max.u.washington.edu writes: >> My father's Commodore 64 has quite a strange problem. When the >> characters on the screen scroll up, the color of the characters changes! : >> We thought that perhaps the color-ram was broken, but the fact that >> the colors stay the same when the screen does not change, indicates that >> the video processor can read the ram correctly. With a basic test >> program however, with which we write a value into the color-ram, and >> read it back again, the value we read back is often not correct. >Sounds like a classic case of the power supply going faulty. Try borrowing >a working power supply for the C64 from a friend and see if that fixes it. As long as people are guessing ... I think it is related to the RAM. It could be an address or data. The data and address path is a little different for the CPU and video chip. The CPU has to read and write the data when it scrolls. I would try switching power supplies because it is easy. But, I don't see how it would cause this problem. -- Rick Clements (RickC@pogo.WV.TEK.COM)