My Scsi 250 zip died on me today, it kept clicking and wouldn't spin up. I had to pull the zip cartridge out with some pliers. I wasn't looking forward to the Ebay gamble so I wondered if I could do anything with a spare Serial Zip 250 that I had. I was actually using it with my PC to exchange wav files with my emu (FAT formatted EOS 4.7). To be honest, the Serial Zip was so slow that I didn't mind sacrificing it. I've got a Scsi card that I used for a while but someone gave me the Serial drive.
Anyway, I opened both up and the drives inside looked similar. They had the same jumpers and connections, makes sense really for something so mass produced. I took the insides out of the Serial, put it in the Scsi and hey presto it works.
I thought I'd post this up because I never knew it was possible to do. Seeing as it's mostly the moving parts that break in a Zip drive I'm thinking of getting another serial on just in case my Scsi Zip dies again. Serial Zips also seems to be cheaper and easier to find than Scsi.
One thing worth noting is that the Zip drive covers had the same design on them, I've seem other types.
Hope this helps.