2 port graphics problems

[RobertT]

Hi all

 

I thought I'd try a pick the brains of everyone here over a problem I am having with a 2 port 5200. I don't have any spare parts to test components, but if anyone has had anything vaguely similar, maybe they can help.

 

When I turn on the console, it shows the splash screen, but sometimes with problems, like the 'copyright' word split over two lines, or the Atari logo splattered all over the screen. It will then go to the start screen, where at times random characters may flash on the screen, but without affecting the abilitiy to start a game and get a few minutes of gameplay without any noticable problems.

 

After this time, the display will start deteriorating with an increasing number of glitches. For example, in PacMan, parts of the maze will start to shift left or right, while other parts will remain in their normal position. In Mario Bros, the display will deteriorate in a seemingly random fashion, with artefacts all over the place, until there is just a mess of colours. However, the gameplay will usually continue - it doesn't hang - and I can still vaguely make out the characters moving, so it is still functioning to some extent and accepting input from the controller, and the sound is fine. In Centipede, there seem to be random shifts in the screen in a manner similar to that in PacMan, and it can also deteriorate to a mess like Mario Bros. What's wierd is that, occassionally, the display will start to reorganize itself to a state where it is almost normal looking, after which it will probably deteriorate again. All this over a period of a few minutes.

 

Any thoughts? Power supply tests at about 14V unloaded, and the regulators VR1 and VR2 seem fine, giving 5V at each of the right legs.

[zylon]

Sounds like a RAM chip or possibly one of the larger IC's.

Atari_5200_Field_Service_Manual.pdf