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I have an older iMac (late 2013) and have been using another iMac as a second display for years. All of a sudden in the past month, the second display comes on for a few seconds and then goes black. I can see the 2nd monitor on the Preferences>Display>Arrangement tab. I hit the Command/F2 combination, the 2nd display lights up and then goes dark again. Any suggestions?
iMac 27", macOS 10.14
Disconnect all peripherals (including the external display) and reset the NVRAM and then retest.
Disconnect all peripherals (including the external display) and reset the NVRAM and then retest.
I tried to reset the NVRAM but the computer goes about half way through the startup process, goes dim and then goes black. I've tried to restore (CMD-R) but the same thing happens. I've tried to start up using a OS disk but the computer doesn't recognize the disc.
I just did a regular restart. The computer restarts and the screen goes black. I plugged in the cable to use the computer as a second monitor and it came on but who knows for how long. Good thing I'm sequestered at home and can keep plugging.
Thanks for your suggestion.
Cables can fail, try another cable.
2nd display goes dark
