• If there are multiple LPT ports on the PC make sure to choose the right one with the +/- keys.
  • The X mark in the cable test program user interface means that the corresponding LPT port input or output pin is in the logical high state.
  • The pinouts and logic functions of 7406 and 74LS86 ICs are shown in the type 1 cable documentation.
  • You will most likely need a voltage meter for troubleshooting.
  • Commodore serial bus signals can be controlled from the C-64 by using the following poke commands:

    
    CLK
    poke 56576, peek(56576) or 16
    poke 56576, peek(56576) and 239
    
    DATA
    poke 56576, peek(56576) or 32
    poke 56576, peek(56576) and 223
    
    ATN
    poke 56576, peek(56576) or 8
    poke 56576, peek(56576) and 247
    
    

  • Look at the schematics and invent test cases like this:"If I put that output to this state then I should be able to control that serial bus signal with these poke commands." Check if your theory holds up. If not, troubleshoot with your voltage meter.
  • Check CLK first and then those more complicated signals.