Will Sony repair your ps3 if you have opened it up before?

If you broke the seal then they will not fix it under warranty. If your optical drive (blueray) drive quit working you just need to go online and put repair blueray in PS3 and you can just buy the laser not the whole drive just the laser for around $19 and replace it yourself there are a lot of repair video on youtube. I fixed mine in 10 minutes. Take your time and remember how you took it apart so you can put it back together. You can video tape yourself doing it.

They charge $50 (the Sony service and support site at the link below says so, I thought it was $150), and they check the seal that you have to break in order to open the PS3. You opened it, you broke the seal. From the warranty (skip to F) ...

THIS WARRANTY SHALL NOT APPLY IF THIS PRODUCT (A) IS USED WITH PRODUCTS THAT ARE NOT COMPATIBLE WITH THIS PRODUCT; (B) IS USED FOR COMMERCIAL PURPOSES (INCLUDING RENTAL); (C) IS MODIFIED, OR TAMPERED WITH; (D) IS DAMAGED BY ACTS OF GOD, MISUSE, ABUSE, NEGLIGENCE, ACCIDENT, WEAR AND TEAR, UNREASONABLE USE, OR BY OTHER CAUSES UNRELATED TO DEFECTIVE MATERIALS OR WORKMANSHIP; (E) HAS HAD THE SERIAL NUMBER ALTERED, DEFACED OR REMOVED; OR (F) HAS HAD THE WARRANTY SEAL ON THE PS3™ SYSTEM ALTERED, DEFACED, OR REMOVED.

You voided any warranty you had when you opened it. That does not mean that they won't repair it for a fee.

"do they just mail you a new one and don't even look at your old one ?" Do you really thing Sony are that stupid?