While most machines that come through our shop are pretty straight-forward to diagnose and repair, there is always room for surprises. We had one such surprise last week with a MacBook Pro that was brought in for two distinct reasons: the hard drive wasn’t recognized and the machine would not boot from CD. While that might sound like a hard drive and optical drive replacement, the technician who diagnosed the issue dug a little deeper.

He did verify that the machine would not boot from CD, and he ordered an optical drive for it. He also verified that the hard drive was not recognized, however, when he pulled the drive out of the machine it mounted just fine in a sled attached to another computer. He could clearly see the volume structure, which passed verification in Disk Utility, and he didn’t notice any unusual sounds from the drive. This led to the conclusion that the issue was the SATA bus on the logic board, and a logic board was ordered for the machine.

The next day, I replaced the optical drive and the hard drive. I attempted to boot to a DVD. The optical drive injected the DVD with no problems and I could hear it spinning in the drive. However, the disk was not recognized in the EFI boot manager. Crap. At this point I’m thinking it could be a faulty optical drive cable or a defective replacement logic board or optical drive. My next step was to attempt to netboot the machine; no dice here either. The netboot server was also not recognized in the boot manager and the boot manager froze twice while looking for devices.

Ok, so now I have a machine that won’t boot to disk and won’t netboot, so at this point I’m thinking it really is a bad replacement logic board. However, I’ve seen this symptom before so there was one more thing to try.

I pulled out the hard drive. The machine boot to DVD, no problem, it also netboot without a hitch. I repeated my co-workers test of plugging the drive into an external sled, sure enough it did mount and displayed the volume, but when I attempted to boot to the drive the tester machine that I was using shut down. Eureka! The issue all along was the hard drive. While it was able to perform some functions just fine, as a boot device it was hanging the SATA bus.

The first volume the EFI boot manager looks for is the internal hard drive, and since this internal hard drive was causing the bus to hang the boot manager wasn’t able to get past it to find the optical drive or the netboot server. Replacing the hard drive resolved all of the issues and we were able to transfer the customer’s data to the new drive successfully!

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