I have bought over 6 of these 3520a DVD drives for workmates and family and I haven't had any problems until i installed one for a fresh system the other day. I hooked up the drive brand new out of the packet to a brand new system and tried to install Windows.. It didn't read the cd.. I thought hrm strange so I put a Lite-On CD drive on it and worked fine.. So I installed windows and when that was complete I put the DVD drive back on and windows installed it as par usuall. I played dvd to test and worked fine but when I gave the system over I was told that the person's driver cd didn't work.. I finally found out that I had the same problems. DVD's work but CDs don't.. I did flash it up but I doubt it was the issue as it didn't work when It was first installed and that it's a firmware issue and more likely to be an issue with the drive itself. So I will be returning it for a replacement.
ps: Funny thing was when i first hooked up the drive before I put it inside the case I was suss about it because I could hear apon inserting a cd a noise that sounded like it was trying to move the parts over and over before it failed to read the cd. Possibly a motor not turning or something. I guess the internal parts could have been damaged somehow.
Hope this helps with others who may have similar issues with this drive