Playstation 2 Slimline Disk Swap Modding Guide
The PS2 Slimline is the hardest to do - It has 3 seperate touch points. For this, you will need some Duct Tape. Thats proper, strong duct tape, NOT the $2 type.

Step 1: Break your warrenty sticker. (This will void your warrenty, but it should be over by now anyway)
Step 2: On the bottom of the ps2, there are 6 screws. undo these. These screws are hidden by rubber or plastic squares - these just pop off with the help of a knife or screwdriver.
Step 3: Carefully take off the top of the ps2.
Step 4: Find the first touch point. This is a tiny switch which is pushed down when your disk tray lid is closed.
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Step 5: This switch switches down towards the front of the ps2. Use a screwdriver or something to see how it goes down. Use a piece or two of tape to hold this down.
Step 6: Find the second touch point. This is a tiny switch which is pushed down near the reset button when your disk tray lid is closed.
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Step 7: As with Step 5, make this switch stay down with the tape.
Step 8: Check both points again.. Those switches tend to come up if they're not stuck down properly. Use more tape if required.
Step 9: Put the Lid back on and screw it up. Replace little square things if you want.
Step 10: Inside the disk tray is a black plastic switch type thing, find it:
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Step 11: This switch goes to the back of the playstation. Tape it so it stays switched.

And you're done! The rest is explained in the PS2 Slimline Disk Swap Guide.