TB/DP & HDMI on mini not working together

[Julien]

Have a Late 2012 mini with a ViewSonic VP2770 DisplayPort hooked to the Thunderbolt/Display port and works great until…… Have Screen Saver set to come on in 2 minutes and Display Sleep in 1 hour. I also have a spare Asus 1080 HDMI monitor to hook up and this is when the problem begins.

…..When I hook up the HDMI all is fine and I have them setup as Extended. When the Screen Saver starts all is still fine. However in about 15 to 20 minutes my ViewSonic (TB/DP) seems to go to sleep (ahead of time and Screen Saver running on HDMI). I can’t wake it up. It seems more like the Thunderbolt /Display port has gone dead or cut off. I have to restart my mini to get the Thunderbolt/Display port to power on my ViewSonic.

What am I doing wrong or what can I try to correct this?

 

[jpietrzak8]

I don't recognize this symptom, but it might be possible to narrow down the problem a bit. A couple of tests:

1) Does this problem occur if only the ViewSonic is plugged in? (Possible issue with the monitor.)

2) Does this problem occur if the ViewSonic is plugged into the HDMI port, and no monitor is plugged into the DP port? (Could be a DP issue.)

3) Does this problem occur if the ViewSonic is plugged into the HDMI port, and the Asus is plugged into the DP port (assuming the Asus can handle DP or you have an adapter); and, if so, which monitor blanks out?

One thing I would note is that the DP standard has been updated fairly frequently, so the 2012 Mini is at this point a bit out of date. If you check the on-screen menu on the ViewSonic, it might show the ability to run in "compatibility mode" with more than one version of the DP standard. Switching between DP compatibility versions might fix the problem...

 

[Neodym]

I also have a problem with the mini's DisplayPort signal. My main monitor is a Dell P2415Q. All three signal inputs are used and I switch regularly between all of them. After a while (can't exactly say if it's weeks or months) the mini would not recognize the Dell anymore after switching. The second monitor via HDMI works fine.

In the beginning I thought the culprit would be the Dell, so I resetted it (plug power for 10 seconds) and usually it would work again. I also switched cables, tried both DP inputs on the Dell and even suspected the Thunderbolt-Passthrough via a DAS box, but could negate that soon.

In recent months, however, more often than not I had to reboot the mini (and once even reset SMC) to make it recognize the Dell again.

So by now I'm pondering whether some internal buffer in the mini (perhaps in the SMC) could be running full after a certain number of input switches on the monitor, as the mini each time has to register the monitor going offline and coming back again later.

Or could it be a problem of El Capitan? I'm hesitating to upgrade to (High) Sierra, as the mini is doing server duties under ElCap with the Server app just fine. And so far the problem reports from early Sierra and High Sierra were not exactly encouraging, especially as it is unclear if that would solve the annoyance.

Any ideas?