Ps3 blueray - auto ejects discs Problem

hello ,

i have a defective ps3, it can read discs but it ejects them during a game and it ejects the discs whenever the power is turned on...

i dont know where the problem is as the lens is okay(can read titles of every kind of media), the sensor takes the discs in and mounting and ejecting actions do work smootly... just that ejecting occurs...it occurs after 8 seconds of disc reading and it does not display any error messages. have you encountered anything like that?