This printer requires genuine HP toner cartridges. If you don't believe me, knock yourself out with the cheapies and you will be knocking at this iFixit guide before too long. You will get a lot of toner blowing out of the cartridges, all over the inside of the printer and the paper tray. Pretty soon your printouts will have color streaks on them. I didn't believe it until it happened to me. After using only genuine HP toner for years I finally bought two sets of knockoffs and my printer was nearly destroyed. After tearing it down again and cleaning all the blown-by toner from everywhere, I'm back in business. This is a great guide. Now where IS that ice cream truck?
The OSA has two screws on top and one underneath. The key to seating the thing properly is to hold the upper right side in so that the unit doesn't rock from left to right. Once you have that stabilized, put the screw in on the upper right. Then the left side, then the bottom.
The Optical Sub-Assembly (OSA) is a real bear to situate properly. The first time I did this procedure (from a different online source), I failed to seat the OSA correctly and the colors printed fine on one side and blurry on the other side. I had to completely disassemble the printer again and seat the blasted thing correctly. I recently had problems with printing and toner blow-by, so I decided to do the same repair again. And this time, even knowing the problems I had last time, STILL failed to seat the OSA correctly! So now I'm using this excellent tutorial to tear the printer down a 4th time! Before I remove the OSA, I'll use some thickness gages to see where I went wrong, and for everyone to absolutely know that the thing is aligned properly. Be back soon!