Rolling picture...sometimes
Posted: 21 Sep 2020 10:08
Hi Everyone,
I have an MTX 512 (with the extra ram board rather than all memory on the main board), and I am having some minor problems with the video image.
When the computer is first turned on, the image suffers from some intermittent rolling and tearing, but then after four or five minutes the image becomes stable. However, when I run certain games (Worm for example), the image will begin to roll constantly, but when I exit out of the game, the rolling stops and the image returns to normal at the basic prompt. Other games, such as space invaders and many others, work absolutely fine with no tearing or rolling. Only a few games have the problem.
From the behaviour, it looks like the issue gets better as components get warmer (other than the games that cause the image to roll, they roll no matter how much time has passed).
I have replaced every electrolytic capacitor in the system, some were way out spec, both on the video board and the power section. As prevention, I also replaced both regulators and the power transistor. This has had no effect on the video issue. I’ve checked all voltages and they are very good and solid.
The monitor is a JVC PVM CRT which also has a Commodore 128 connected to it, and the picture from that machine is rock solid. However, I am trying to source a different monitor to rule that out of the equation.
I notice that there looks to be some sort of trimmer capacitor on the PAL video board and wondered if that has any effect before I start turning it.
I think that the sync signal comes from the video chip, could this sort of intermittent issue be caused by a faulty VDP chip? I’m going through the machine to give everything socketed a thorough clean as well.
Thanks
Mark
I have an MTX 512 (with the extra ram board rather than all memory on the main board), and I am having some minor problems with the video image.
When the computer is first turned on, the image suffers from some intermittent rolling and tearing, but then after four or five minutes the image becomes stable. However, when I run certain games (Worm for example), the image will begin to roll constantly, but when I exit out of the game, the rolling stops and the image returns to normal at the basic prompt. Other games, such as space invaders and many others, work absolutely fine with no tearing or rolling. Only a few games have the problem.
From the behaviour, it looks like the issue gets better as components get warmer (other than the games that cause the image to roll, they roll no matter how much time has passed).
I have replaced every electrolytic capacitor in the system, some were way out spec, both on the video board and the power section. As prevention, I also replaced both regulators and the power transistor. This has had no effect on the video issue. I’ve checked all voltages and they are very good and solid.
The monitor is a JVC PVM CRT which also has a Commodore 128 connected to it, and the picture from that machine is rock solid. However, I am trying to source a different monitor to rule that out of the equation.
I notice that there looks to be some sort of trimmer capacitor on the PAL video board and wondered if that has any effect before I start turning it.
I think that the sync signal comes from the video chip, could this sort of intermittent issue be caused by a faulty VDP chip? I’m going through the machine to give everything socketed a thorough clean as well.
Thanks
Mark