No external display from MBP 2012 on Catalina

[Topher06]

I own a MBP mid-2012 non-Retina i7 with 16gb RAM running the latest Catalina 10.15.7
I use a MiniDisplayPort adapter for HDMI and another one for VGA. Both work nicely on my MBP late-2008 on Yosemite when linked to my LG monitor.
But the latter is never detected by the MBP 2012 (and yes, I did press the option key to detect monitors in the preferences panel).

I have tried the SMC reset, PRAM, NVRAM, safe mode start, the start-up-the-Mac-then-shut-it-quick trick, various Terminal command lines, but still no monitor...
I cannot tell whether the Catalina upgrade has anything to do with it because it was freshly installed when I bought the machine. However, it's making me want to format everything and switch to Mojave if this means my HDMI/VGA will work as it is rather essential for me.

Any tips are more than welcome ! Thanks a lot !

 

[brianmowrey]

I hope you haven't bought a 2012 with a broken mini DisplayPort.

To drill down further would require more isolation. Does the Thunderbolt Bus show in System Information? Does a second display show in System Information> Displays when you connect the display? Does a different HDMI display work? Does a different adaptor work (probably not, since the current adaptor works on the 2008)? Does mDVI to VGA display work?

Or, just skip to reinstalling Catalina in case it's just a bad install.

I don't think you will get any advantage from downgrading to pre-Catalina - mDVI to HDMI 1080p works fine for me on Catalina - but it's not very difficult to do so by creating a bootable installer if you want to try.

 

[Topher06]

Thanks for your help, Brian !

Actually, my MiniDisplayPort adapter doesn't seem to register as a Thunderbolt device. When I plug it in to my 2008, it says "no device connected" under the Thunderbolt tab - and yet it works.
Of course, on the 2012, it says the same thing but doesn't work - and doesn't show the 2nd display either...

Unfortunately, I don't have another HDMI display or genuine Thunderbolt 1 cable or Thunderbolt-powered device to test things but it seems to be the next step for me. Also run some kind of hardware test software I guess. If everything fails, I'll have to try reinstalling Catalina or downgrading to Mojave since many users seem to blame Catalina for their HDMI issues.

Still looking - and still open to suggestions ! ?

Thanks again !

 

[justashooter]

MiniDisplayPort adapter would not appear under the Thunderbolt tab, it is a graphics/display adapter and should appear under that tab. The adapter should appear under the graphics/display listing on the 2012, it will not appear under the Thunderbolt tab. Thunderbolt devices will never appear on the 2008, thunderbolt did not appear until 2011.

 

[brianmowrey]

Yeah, I wasn't sure what thunderbolt tab refers to, so scratch that. But if "doesn't show the 2nd display" refers to the Displays tab, then that suggests a hardware or OS problem. If you have a quality local repair shop they can probably test a different display / connector setup for you on the spot just to rule that out. Or, you can skip to reinstall OS since that's non-destructive anyway.