A first-generation MacBook came in the other day because the sleep indicator light wasn’t working. This is actually a tricky one to diagnose because so many components are involved in making that little light work. The light itself is powered by the SATA cable, which also powers both the hard drive and shuttles data to and from the hard drive. The SATA cable ends with a socket that the hard drive plugs into, and that socket has a tiny connector for the flex cable that powers the sleep light.
Of course, the sleep light isn’t available as an individual part. That’d be too easy. Instead, it is part of the bottom case, and swapping the bottom case requires complete disassembly of the MacBook.
On a hunch, I swapped out the SATA cable, and plugged in the sleep light. No go. I then swapped in a known good logic board, which also didn’t help. Thinking the LED itself was most likely not the cause, I grudgingly ordered and installed a bottom case. That didn’t work, either.
By then, it was 6:30 at night and I was ready to go home and make some dinner. As is often the case, I think about work at home and realized that I skipped the all-important test: I never booted the machine off a known-good MacOS X installation, such as the computer’s restore disk. No, that didn’t work, either.
I took the machine apart again and double-checked my work. I re-seated the connection from LED to SATA socket, put the machine to sleep, and let out a sigh of relief that the light was working again. Since I’d replaced so many parts in diagnosis, it’s hard to know which component was actually to blame. I’m willing to bet it was the connection all along.