Data drive is an IBM 20GB 60GXP DeskStar, model IC35L020AVER07-0, P/N 07N6902, and MLC H32161. Wasn't being detected by BIOS on several computers, and wasn't being detected by IDE to USB converter either. Made a constant clicking noise.
Ordered a hard drive to match, giving the model number, part number, and MLC number from an online vendor. Received donor drive today, and it came as the same model number, but was P/N 07N7402, and MLC H32368.
Originally figured data drive's problem was bad heads, so performed simple head swap in a 99.97% HEPA environment in a glovebox cleanroom. This drive only has one platter, so only two heads. Paper kept heads apart, they never touched.
Data drive is now recognized by BIOS, and I ran ddrescue for a little while. It's going extremely slow, about 15kB/sec, which would take about 16 days to complete.
I tried several starting input positions (3G 5G 10G 15G 17.5G), so I know it's not just that the beginning of the drive has some problems.
I also took the heads back out and reseated them in case they weren't quite aligned correctly.
I don't mind if it's just going to take that long. What worried me and made it stop was that I don't believe the platters are damaged, and the drive is making almost a scratching noise and going so slow. On the side of the platter I can see, there are no visible problems. There's no silver dust anywhere, and the pillow doesn't have anything on it. Since it's a single platter drive, I could take the platter out to check for damage on the underside.
You can listen to a mp3 recording of the almost scratching noise the drive is making with the new heads at:
http://sigma.homeunix.com/IBMHardDriveScratching.mp3 (Can hear it starting around 18sec if you can hear it in the background of the motor noise.)
I'm worried that if I let it continue, I'll damage the platter and/or heads. Should I continue, letting ddrescue run for two weeks? Could the new heads be bad, albeit not as bad as the original heads since it's now being detected by BIOS? Could the new heads not be fully compatible, since the donor drive doesn't match P/N and MLC numbers? Could a faulty PCB be causing the problem? Should I try using the donor drive's PCB, even though it's not an exact match - or should I purchase elsewhere an exact match for a new donor drive? The data and donor drive PCBs aren't identical, they are laid out slightly different. It looks like there's an NVRAM on the PCBs, although I'm not 100% positive.