Chosen Solution
Hello, During Catalina update (coincidence) I lost the display picture and the reason seems to be some kind of hardware fault. No startup chime, only backlight turns onResets of PRAM etc. didn’t improve the situationNo external display output (miniDP)Already disconnected battery and display cable multiple times, no changesWhen powered on the fan starts up for a few seconds 2 or 3 times then runs without stopping anymore while backlight is lit up Any other chance to narrow down the reason a bit futher? Thanks in advance.
How soon did you panic? The system restarted after what you thought was the finish point of the upgrade and noted this? And then you powered down your system right away? If thats the case I fear you may have messed your self up! Apple now upgrades the systems firmware for different issues. As an example if you where using Sierra beforehand then your system needed to do a file system update from HFS+ to APFS which does take a bit of time. The second is the systems firmware also needs an up date for the new file system to be recognized, and lastly Apple now stores malware and other nasties signatures as well here’s more About background updates in macOS Mojave So what to do?? At this point restart your system and let it be! Let’s see after a two to three hours if the system will recover its self, if it won’t then you’ll need to visit an Apple Store so they can use their magic to fix this.
