Getting RSOD on 2 different ps2s

[Schmendy]

I've modded 2 different PS2's, both with the Magic 3.1, yet I'm always getting the red screen of death, except with original ps2 games. I'm sure it's not a laser issue, as they both worked perfectly pre-modding, and I've checked wires but can't seem to find a fault. Is there anything in particular I should look out for? The fact that I'm getting it with 2 different model PS2s seems like I'm probably doing the same thing wrong on both.