Atari 400 NTSC diagnostics

    Hello,


    I have an Atari 400 NTSC with 48k RAM. I thought it was working within parameters as it was loading programs from cartridge just fine.
    Today I have decided that I do some software exploration on it as this is my first Atari and I have no idea about it really. I have built an

    SIO2PC adapter and enslaved my PC as drive emulator with RespeQt. This setup seems to work fine.



    When I started to test out demos written for the 400/48k NTSC realized that only some of them will load, most of them will

    freeze the machine, while others run but with jumbled screen content.


    Like the Swan demo here:

    atari.gif


    I flipped through the service manual to figure out what to poke, but seems like there is no way to do diagnostics without a SALT cartridge.


    Or is it?


    ( tried several diag programs i have found online, none of them will start )


    Thanks for your help in advance,

    m.