The original code in the 586220 cartridge was made for the C64 and it generated lots of errors when used on the SX. Parts of the code were rewritten so the same cart can now be used with the SX as well.
Of course a complete test of all the ports requires the "octopus" cable, the same as used with earlier C64 and C128 diagnostic carts. A different keyboard dongle must be made for the SX which has a 25 pin D female recepticle on the underside of the computer. As with the C64 & 128 keyboard dongles, this one cross connects all the columms with the rows (0 to 0, 1 to 1, etc.), as shown in the diagram.
The internal 1541 in the SX must be disconnected (unplug P11 on the I/O board or P19 on the FDD board) so it doesn't corrupt the readings. Since there is no cassette port on the SX, that will show "open" and if there is no adapter plug on the keyboard connector, it will also show "open" or "bad". If any other than the original SX Kernal ROM is installed in the SX (such as JiffyDOS) the cart program will default to C64 diagnostics and the readings will show errors. 