This might problably help:
Serial Number on rear of machine begins with:
version 1 = serial number (refer to yellow rectangle in right of image) start with "U1" and has 10 case screws.
version 2 = serial number (refer to yellow rectangle in right of image) start with "U0" and has 10 case screws.
version 3 = serial number (refer to yellow rectangle in right of image) start with "U2" and has 10 case screws.
version 4 = serial number (refer to yellow rectangle in right of image) start with 'U3' 'U4' 'U5' or a 'U6' and has a total of 8 case screws.
version 5 = model number contains the letter 'R' (refer to the red rectangle in right side of image) at the end (example SCPH-30001 R).
version 7 = 3900X is the new PS2 Version 7
Once you have esatblished what version you have, examine the limitations using this chart:
Version 1 - Basic playstation 1&2 Games no dvd-r,dvd-rw compatability, NO DVD+R, NO DVD+RW COMPATABILITY
Version 2 - Basic playstation 1&2 Games dvd-r,dvd-rw compatability, NO DVD+R, NO DVD+RW COMPATABILITY
Version 3 - Basic playstation 1&2 Games dvd-r, compatability, NO DVD+R, NO DVD-RW,NO DVD+RW COMPATABILITY
Version 4 - Basic playstation 1&2 Games dvd-r compatability, NO DVD-RW, NO DVD+R, NO DVD+RW COMPATABILITY
Version 5 - Basic playstation 1&2 Games dvd-r compatability, MILD DVD-RW, MILD DVD+R, MILD DVD+RW COMPATABILITY
SECOND GENERATION PS2
VERSION 7 - (SECOND GENERATION PS2) Basic playstation 1&2 Games DVD+R,DVD+RW,DVD-R,DVD+RW compatability