How to modify the 55xx machine
Take a note of the pin connections
Ensure there is not a disc in the machine, remove the parallel port cover on the back, flip your machine over and remove the 6 retaining screws
Flip your machine back the right way and lift off the top cover, remove the drive unit by gently pulling out the ribbon cable and the small motor supply plug, lift the drive unit clear and set it in a safe place
Disconnect the second ribbon cable and the power supply cable, remove the three phillips screws holding the plate and lift it clear, you might have to wiggle it a bit as it tends to hang on the locating pins
Remove the 5 phillips screws holding the system board in place, lift the board out and flip it over
This is the back of the board with the mod chip fitted and secured
Here's a close up of the finished product, You can use a glue gun or double sided tape to secure the mod chip in a area that does not come in contact with one of the raised earthing places in the bottom of the case, a small piece of tape keeps the wires from flopping around