I installed a DUO 3 chip in my PS2 Slim (70012) this week. Everything worked perfectly except the PS1 games. My PSTwo can boot PS1 games, but the video output is blurred and is not centered in the middle of the TV screen (PS2 games are fine). When I play Tekken 3 (no matter the original version or the backup version), there are a lot of 3d rendering errors in the actual fighting scene.
I didn't try PS1 games in my PS2 Slim before, but I did try the same games in another old PS2 non-slim, no video centering problem or rendering error at all.
I'm wondering whether the PS1 compatibility problem was caused by the DUO3 chip, my soldering process or the PS2 slim itself ?