skjoldhammer Posted March 30, 2021 Share Posted March 30, 2021 Hi, I have a strange problem. I did a AV mod on my PAL 7800 atari (REV C PCB) but the 7800 games stopped to display. If I put a 2600 cartridge it runs perfectly with stable image and sound. If I power it up without any game or with a 7800 cartridge it will not display any image. But I can hear the sound of the 7800 game running in the background. Any clues what did happen here and how to fix it? Greetings, Bjørn Quote Link to comment Share on other sites More sharing options...
marauder666 Posted March 30, 2021 Share Posted March 30, 2021 Post a picture of the wiring Quote Link to comment Share on other sites More sharing options...
+DrVenkman Posted March 30, 2021 Share Posted March 30, 2021 Sounds like you’re getting TIA video output but not MARIA. Post photos of your installation. Quote Link to comment Share on other sites More sharing options...
msxtrd Posted March 30, 2021 Share Posted March 30, 2021 I did lift the video pad on top board and had to pull an air wire. Though I'm not sure if this is connected to anything bacause it did not change anything after reconnecting. Quote Link to comment Share on other sites More sharing options...
msxtrd Posted March 31, 2021 Share Posted March 31, 2021 Could the Maria chip be damaged somehow? Does Tia or Maria generate the sound in 7800 mode? I remember vagually that I had 7800 model years ago, then I sold it, but kept few 7800 cartridges. Afterwards I did get this one somewhere. It did have the big cap at the corner loose. Looked like someone replaced it. Just don't remember ever testing 7800 games on this one before. Is there a way to thest somehow if the video comes at all out of the Maria chip? Quote Link to comment Share on other sites More sharing options...
+DrVenkman Posted March 31, 2021 Share Posted March 31, 2021 3 hours ago, msxtrd said: Could the Maria chip be damaged somehow? Does Tia or Maria generate the sound in 7800 mode? I remember vagually that I had 7800 model years ago, then I sold it, but kept few 7800 cartridges. Afterwards I did get this one somewhere. It did have the big cap at the corner loose. Looked like someone replaced it. Just don't remember ever testing 7800 games on this one before. Is there a way to thest somehow if the video comes at all out of the Maria chip? Audio is produced by the TIA in all 2600 and all 7800 games except Ballblazer, Commando or some modern homebrews that have sound chip in the cartridge. The ideal way to check for video output of MARIA is to put a 7800 game in the console, power it on and then use an oscilloscope to check for output on pins 42-48, the video signal outputs. A cheap logic probe will work in a pinch, but an oscilloscope will let you see the signal waveforms. Pay especially close attention to pin 48, which is the SYNC signal. You should see a regular pulse there for the video horizontal sync signal. On an NTSC system that’s 15.7 khz; I don’t recall what it is for PAL. A scope or logic probe will show whether it’s there or not, at least. With a copy of the schematics (available here on AtariAge) and a multimeter, you can then figure out if you have continuity between the MARIA pins and the rest of the components in the video output circuit, and if the signals are properly showing at the various discrete components on the board. Quote Link to comment Share on other sites More sharing options...
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