The default values of the PS1 drives are between 940 - 970 ohms. To read burned CDs you have to go down a bit.
Warning ! Before you work on the open console, be sure to remove the power! Pull the plug!
Reducing the resistance, will increase the wear and tear of the laser ! If you go down in steps of ten and the CD is read correctly do not further reduce the value, that is useless.
CD's MUST be burned with a maximum burning speed of 4x, because the PS1 laser cannot deal with burn errors. If your burner only supports higher speeds, get another one, because then the games will most likely not work.
This Tweak is intended for 7000er consoles (750x, 700x)! Other PS1 consoles may have a bias & gain on the motherboard. If this value is adjusted then there are other instructions for it.