I have several untrustworthy 4 GB 50 pin SCSI external drives (the data is backed up!) that have similar unresolved symptoms if stored for a while. After some visual inspection yielded nothing I did some simple experimentation including power supply substitution and found that repeated power up cycles eventually would spin the disk up. Initially the spin up would terminate quickly. Subsequent power ups yielded slightly longer and longer spin up periods and higher rpms reached before drop out. Snap rotating the drive to relieve any stiction tendency also seems to help sometimes. Finally after enough of these prematurely terminated spin ups ( maybe 4 to 8 ) the disk would reach final speed and stay up. After leaving the disk on for a while, then turning it off, the next turn on cycle would come up to speed in a short time, more rapidly than any of the previous attempts. I haven't ruled out congealed ball bearing grease, bad electronics, electrolytics or a cold solder joint, but my two units act like the motor drive is not quite up to overcoming some friction source before some timeout or cutout occurs. When the disk comes up to speed and runs for tens of minutes, it is good for subsequent fast spin ups for many days thereafter. And once running, I have yet to see the disk drop out suddenly, as might happen if a solder joint was bad or connection intermittent... [?]