922      iPhone_iPad_Mac_apple

iMac (late2014) boot issues

This is a used iMac 27in late 2014, i7 4GHz, 16MB RAM, 512GB Apple SSD that I just acquired.

MacOS Sierra 10.12.6 freshly installed from a bootable USB stick, and also reinstalled per the Install app (app store download) because of the problem below.

Regular startup works as expected.

Issue:

None of the key modifiers for special startup sequences work as expected. Holding Cmd-R (for recovery partition), Cmd-opt-R (for internet recovery), D (for diagnostics), opt-D (internet diagnostics) all lead to a black screen, and nothing else happens for minutes until I hard-shutdown the machine.

Holding the option key just boots normally, even when bootable USB stick is inserted; if this would be ok, one should see the regular boot volume, the recovery volume, and the USB stick.

The only way to make the iMac boot from the USB stick is either by (1) selecting it from the Startup Disk control panel and restart, or (2) by having the internal drive in a non-bootable state, e.g. erased or encrypted.

Why would I mention encryption... the real bummer is that I cannot enable Filevault 2 for my internal drive: After switching FV2 on, the system requires a restart. And after the restart it won't boot from the drive anymore - and there also is no request for the password. Whatever macOS usually does to relaunch into the encrypted drive is not working.

All this points to one suspicion: I must be dealing with a hardware or firmware issue that messes up the startup management. It does not seem to be software, from what I can tell: System is freshly installed. And internet recovery and internet diagnostics should work regardless with a late 2014 iMac during startup - but these services don't even launch.

Verified:

- The recovery partition exists (use Terminal command: diskutil list; and I also checked that the usual Apple files are on there)

- This is not a keyboard connection issue. I used both Apple wireless and a USB keyboards, and there is no difference. Also, the keys are definitely recognized, otherwise the machine would always boot normally and not enter the black screen.

- NVRAM reset does work, and I resented twice.

- I also performed a SMC reset

Thanks to those that are familiar with this issue and can confirm a hardware fault, or somehow know other ways to narrow down the cause. I have worked with Macs professionally for about 25 years and this is the first time I am stumped.

最後更新：2017-09-27 18:03:58

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