I have a MBP mid-2012 (pre-Retina) running Mojave or High Sierra. I use the latest version of SwitchResX to handle the external monitor rarer resolution of 1440x900, surely not too many pixels for the older Intel graphics chip. Video adapter is a Thunderbolt 1-to-VGA.
Previously, I used a DisplayLink USB3-based video adapter to light the second monitor (legacy from a slightly older MBP with a burnt Thunderbolt chip) with few issues, except the ginormous CPU consumption that made it impossible to use said adapter for anything else than text or short animations, the single reason why I want to revert to the Thunderbolt adapter. USB3 was never made for streaming video data, no matter how good the compression and algorithms.
Problem: Every time I try to connect the external monitor in Mojave, the OS freezes with a short delay. However, briefly before freezing, SwitchResX does acknowledge the external monitor presence, albeit at an extremely low resolution of 800x600. If external monitor is plugged in before boot, boot doesn't proceed.
- Same maneuver in High Sierra triggers the same behavior.
- Resetting PRAM then SMC has no effect.
- Disabling SIP has no effect (Off the top of my memory, since I cannot access local recovery partition for Mojave)
- Connecting as a different user on either OS triggers same behavior
- Last time I checked, booting in safe mode on either OS allows the external monitor to turn on. Of course, running in safe mode just to get a working external display isn't a viable solution.
Not tried: Full OS reinstall. While it would be pretty radical, it is extremely time-consuming and may or may not yield results
What could be happening here?