Sony PlayStation 2 Repair Manual page 7

Remove the 4 screws indicated in the picture. You will then be able to remove the expansion bay assembly.
There is nothing attached to it.
Then pull up on the power supply board to remove the pin connector from the socket. Then fold the power
supply board open like a book, leaving the power connector cable attached. You can then check the fuse
(marked on the right) or remove the power switch cable and check it (marked on the left)
When you are done and ready to reassemble just reverse the procedure. Just be careful when plugging the power
supply board back into the connector to make sure all the pins line up correctly.