You guys with the "busted" drives need to use a multimeter, instead of relying on crappy markings and such.
As stated, doing a tweak is "at your own risk" - but it really shouldn't be that bad for a patient person willing to use the correct tools and put up with the repetitive process of disassemble-tweak-assemble-try until getting the thing correct.
Another cliche in play here is "Your Mileage May Vary" - meaning one person's settings may not work for another.
Tweaking those pots essentially changes the power to the laser diode (lower ohms means more power). Adjusting the ohms too low will most likely result in a shorter lifespan for your drive's laser (and thus, the drive itself).
If your system reads the media it's expected to read, LEAVE IT ALONE. Compatibility generally follows the following:
Philips-
- DVD-R
- DVD-RW
- DVD+R
- DVD+RW
- CD-RW
- (some?) CD-R
Samsung-
- DVD-R
- DVD-RW
- (Some) DVD+R
- (Some) DVD+RW
- CD-RW
- CD-R
Thomson-
- DVD-R
- DVD-RW
- DVD+R
- DVD+RW
- CD-RW
If it's marked "(some)" then it might work, but don't expect it to. Only try tweaking it if it doesn't work with a media it should work with.
As for CD-RW compatibility, try a lot of brands first... some brands NEVER work for CD-RW on the Xbox. Also, test it against a friend's Xbox, if possible.
In short, don't tweak if you don't have to. If you are desperate to get CD-R/RW working, think about getting a DVD-R burner, instead.