skjoldhammer

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