Mod Chip Problems?

[Seven Kevin]

I have an older PSX and use a goldfinger with excellent results.
My friends machine has no parallel port so I suggested he use a mod chip. We made sure the mod chip matched the model number and ordered it.
I didn't see the installation but he said the directions were followed carefully (theres only four wires)
His son fired it up and games (even original) wouldn't play. He removed the mod chip and games still won't play.
Hoping someone might help us out in what might have went wrong and if anyway to correct it.
Could have the mod chip damaged his machine?
I have never (that I can remember) seen anyone posting about mod chips being faulty or not working so assume the success rate of installation is very high.
Appreciatte any information on this problem Thanks in advance.