I Got The Power
I recently had a blinding flash of insight: even though external USB 2.5″ hard disk drives can get their power from a USB port without needing a separate adapter, all USB ports are not equal. Some have enough power, and others don’t.
When I bought an external enclosure for an old 2.5″ notebook HDD a while ago, I puzzled over the odd USB cable that came with it. The cable had a mini-B plug on the end that plugged into the enclosure… but on the other end, it forked into two standard-A plugs. Huh? I didn’t get it. Was it supposed to be so you could use two USB devices off of one port? But if that was the purpose, then on one end it should have had a standard-A to go into the PC, and on the other end it should have forked into two plugs, the mini-B and maybe a standard-A. Now I get it — this cable is actually supposed to take up two USB ports on your computer, in order to draw enough juice to spin the HDD.
I had been mystified by the iffy startup behavior of this HDD for a few weeks — sometimes it’d start up OK and sometimes it’d repeatedly spasm, trying to spin up — but the power thing makes it all clear now. The (probably too long) USB cable I’ve been trying to use with the HDD isn’t giving it enough juice. As it happens, my computer has another USB cable that I’ve been using for years to hotsync my Palm. Since the Palm has its own power cable connected to a dedicated power adapter, it uses USB only for data, not for power. So I tried switching devices, so that the HDD uses the formerly-for-the-Palm cable, and the Palm uses the not-enough-juice-for-the-HDD cable. Now both gadgets are happy. Problem solved.
Y’know, you’d think I would have figured this out a long time ago. D’oh!