ps2 problem with psx game

[ridiculoso]

i have recently chipped my ps2 with neo2.2. I made a backup of iss pro evolution2 (for psx) using clonecd, when i play it on the ps2 it boots ok and everything, but sometimes during the game everything slows right up - and then it becomes unplayable cos it plays frame by frame.
Could it be the copy or a dodgy chip installation causing the problem?? - point 2 was tricky the component got a bit burnt!