How do you exactly use PS2 back-ups with modchip?

[MTXLZR]

try following these instructions: hope they help

PS1 Games (PAL/NTSC originals and backups) - normal boot!
Note: When in PS1 mode, the PS2 doesn't display NTSC disks full-screen. This is due to the firmware inside the PS2 not switching into NTSC mode. There will be a black gap on the bottom of the screen on all NTSC disks because of this.

PS2 Games (PAL originals) - Hold reset until the blue eject light comes one (about 1 second). This turns the modification OFF.

PS2 Games (PAL/NTSC backups) (some games work with 1st method, others with the 2nd method, some with both methods)

Method 1: Startup with AR2 CD1. Select "Start game", then "Without codes", press the eject switch, swap the disk with backup, close the tray and press "X" on joypad.

Method 2: This method is mainly used for EA Sports Games. Put the AR2 CD1 into the tray, switch the unit off (red led), hold down the reset switch to turn the unit on, but keep holding it down until the AR2 menu appears (and the CD stops spinning). Let go of the reset switch and the tray will open up, you now have 4 seconds to swap the CD with the backup before the tray will automatically close. Select "Start game", then "Without codes", and press "X" on joypad.

The chip is designed for use with the AR2 version 1.3. It may not work with other versions