I thought I hit the lottery when I got my new XBOX and lo and behold there was a Samsung drive! I bought the XBOX just to mod it, so I quickly set about it. I used Slayer's to set it up from CDR and it went flawlessly. Once I got ahold of some games to try, I had a hell of a time getting the originals recognized. I would try again and again, to get "Unknown" or "No Disc", and sometimes the disc would load... well last night I had enough. I was going to order a 616T or F to mod, but I figured I might as well dive inside my Samsung and see what I could do.
There are already good tutorials detailing the disassembly and removal of the DVD drive, so I won't bore you with those details. Once you have the drive removed, remove the four screws on the bottom of the drive and remove the bottom cover the screws were securing. Your drive should look like this:
You can see the laser unit, and the two potentiometers are located for easy access. I couldn't find any posts or tutorials regarding the Samsung POTs, so I wasn't sure which was the pickup I should adjust. I scraped some of the epoxy and measured the resistance of each POT. One was at about 2.3K ohms and the other was at about 960 ohms. I decided to adjust the POT that was at 960 and see the effect, then I would try the other if I saw no improvement. As mentioned in the existing POT tuts, be very careful scaping off the epoxy holding the POT screws in place. I personally removed my whole laser and did it under a microscope with an exacto tip, but that is because I had the scope handy! The potentiometes are very touchy and sometimes jump huge amounts when you adjust them. It took some careful tweaking, but I got the setting to 865 ohms, which I thought I would try. The POT I adjusted is indicated in this picture, and I was measuring the resistance between the POT terminals labelled 1 and 3.
I reassembled and tested the unit, and I couldn't be happier. The performance difference is like night and day! I can load all the originals I try, and the XBOX demo discs that I could NEVER get to load, load right up without a hitch. If you have the steady hand and proper equipment, I'd measure the POT resistance while making the adjustment with a plastic screwdriver. A metal screwdriver will throw off the resistance reading because of the design of the POT. Don't bother trying to measure the POT while adjusting if you only have a metal screwdriver handy. Just go through trial and error - tweak, measure... tweak, measure...
I just provided these pics in hopes it may help answer someone else's questions. I'd suggest you only try this if you REALLY know what you are doing, and I completely agree with many others who've posted that you really should have a scope to do laser calibrations. I take no responsibility if you fry your XBOX or yourself!