Q: replacement UJ-875S reading only DVDs not CDs

You sure it is a blank DVD-R, and not a DVD-R DL? DVD-R DL was not as compatible on Powerbooks as it became later on in MacBook Pros. And are you using Ritek, Taiyo-Yuden, Verbatim DVD-Rs, or some other brand? And are you using DVD-Rs that were stored in a jewelcase and not in a spindle? And are you not writing any pen/ink on the disc itself, or not using sticky labels?
Cause if the answer is no to any of these questions, you may have yourself a problem.

All other brands use unreliable wax for DVD media. Some may work, some may fail miserably after a few weeks.

Spindles unfortunately do not keep the gap between each disc all the time, and the underside of a disc can get scratched anytime you move the spindle with the label side of the other.

Sticky labels can cause imbalance. Ink can get through to the wax level, and make a disc unusable.

Still they are TDK, and not one of the brands I found out are the ones that own the patent for the most reliable sub straight. Try one of the more reliable brands.

I don't think you are reading what I wrote either. Discs can fail. Especially more frequently, and sometimes in a few days to a few weeks if they are not from the companies I list. Try high quality discs.

In other words, if you aren't using the kinds of discs I list, you might as well be sticking pieces of cardboard into the drive in question. They may look good on the surface, but issues with discs are microscopic in nature because of how high intensity the laser. If those tolerances are not met by the manufacturer, there is no guarantee your disc will last at all. And while some other drive manufacturers have higher tolerances, these drives are potshoot when it comes to anything but high quality discs. Sometimes they'll work, and sometimes they won't.

Have you tried Verbatim, Ritek, or Taiyo-Yuden discs? Until you do, you will never know if the issue is the grade of disc or not.

That may be a problem with their drive.

If you knew I was going to say it, why waste our time asking the question, we are all vollunteers. If you are so all knowing, troubleshoot your problem yourself. And no you can not equate any two drives with identical sounding issues. My advice, shop around on http://www.xlr8yourmac.com until you find the most relable drive/firmware out there for your version of Mac Os X. And if you still have a problem, the media or the drive interface on the logicboard must be at fault. You have reviewed the only quality media out there. If the same disk fails on one machine with the same drive and operating system it is the interface on the logicboard. Otherwise the same media should always fail.
Eliminate the probable, and when all else fails the improbable must be true.

USB will not boot PowerPC - Yes it will... I know because I use it all the time.. I don't mean to hijack anything but people need to know that this has been done time and time again.. the verdict is that most if not all PowerPC based macs can boot off USB Drives.. I am not knocking firewire.. I think firewire is the way to go for both intel and powerpc macs, but its good to have the USB option available...

This has been proven since the days of Tiger(2006).. Its simple.. all you do is go into open firmware and type the following:

If its one USB device hooked up, type: boot ud:,\\:tbxi
If its multiple USB devices hooked up, you need to know what the device label is for example:

boot ud:3,\\:tbxi - Boot the device associated with the 3rd slice.

And to really knock your socks off, I just restored from image the apple hardware test from my powerbook g4 restore disk to my USB drive... went into open firmware and typed: boot ud:,\\:tbxi - Voila! it booted up Apple Hardware Test in less than a miniute!

For most people I don't recommend this, but to say that PowerPC macs can't boot off USB 2.0 devices? That idea has already been proven since 2006.

I don't know about 10.3 or 10.2.. but I do know that USB 2.0 booting on PowerPC started with 10.4.3 and up to 10.5.8.

I have the same problem. Bought and installed a UJ-875S in my powerbook G4 1.67 GHz 15-inch. It plays DVDs, but not CDs. I'm running leopard 10.5.8, and have even tried completely reinstalling the OS. Same problem. Been searching the web and seen this post and one on the apple forums with the same problem, but no solutions.

This is not a problem with the media. The same audio cds will play fine on my macbook pro 17 inch 2.8 GHz, and played fine on my powerbook's previous drive before that one died. This must be due to the drive itself, or some driver missing.