PS4 pro disc reading issue

Hi all, looking for some pointers. Acquired a pro that takes discs but gives an unrecognised disc, blu ray and regular dvd. I have changed the laser deck twice (surely i didn’t buy two duff ones) but no luck. Just curious if anyone thinks that the BD7764 chip might be to fault or if there is anything that the driveight have issue with even if it appears to behave normally. Thanks for any help.