Slimline PS2 probs

Before i go down the road of warranty etc, can anybody give me any pointers as to why my New Slimline PS2 (SCPH-70003) struggles to read some of my old PS1 originals. It is not chipped and i have only had the unit just over a week. PS2 games all seem fine, although Brian Lara 2005 has locked up a couple of times, i have around 10 PS2 games at the mo and all seems well. I have around 12 PS1 originals of which 5 either refuse to boot or hang during loading or gameplay. I have tried the following,

Turning the unit upside down & on its end.
Cleaning the lens.
Cleaning the disc.
Checked the discs for errors in Nero.

I have just tried these games on an older PS2 and they all work fine.

Should i persue this further, or is compatability to PS1 games not guaranteed. My worry is that i have got a weak laser, (just like on my PS1 years ago!) and that this situation will get worse, and it will cost me to fix it

I would be grateful of any suggestions. :slight_smile: