SOLVED Dual External Monitor Troubleshoot

Apr 24, 2019
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Good Morning Mac Users,

Let's see if we can solve this puzzle:

MacBookAir6,2 => thunderbolt => StarTech Thunderbolt 2 Docking station (TB2DOCK4KDHC) => dual monitors: Acer P235H @ 1080p via HDMI && HP ZR24w @ 1080p via MDP to DisplayPort (note the MDP cable is plugged into the thunderbolt port on the dock)

Okay, so the trouble is I can get each display to send, but not both. With both monitors plugged in, the Acer monitor is prioritized, and the HP monitor does not detect any signal. As I said, I have tried each monitor separately and they work. Obviously, the goal was to get both monitors to display!

Things I have tried:

- Checking displays in the system report. Both displays are shown. It seems the dock won't send the signal to the HP monitor, but it will ack the mac that it detects.

- Setting both monitors to the same resolution. The HP monitor is 1920 x 1200p native, so I changed it to 1080p - no improvement.

Things I suspect:

- The mac I am using is Thunderbolt 1. Perhaps it does not have enough throughput to support both monitors. Frankly, I find that dubious because Thunderbolt 1 supports, what, 10Gbit/sec? That should be plenty for two 1080p monitors.

- The built in display needs to be turned off so that the graphics processor can deal with it. I use an Intel graphics 5000 chip @ 1.5 GB graphics memory. Maybe the dock does have enough signal from the graphics chip to send it out?

- Simple compatibility issues. The docking station is for Thunderbolt 2 compliant devices, specifically MacBook Pro w Retina. I really doubt this is the issue, as all my periphery devices are working on the dock - one monitor, mouse, keyboard.

- Thunderbolt Docking Station

- Macbook Air

- Acer Monitor

- HP Monitor

Thanks guys!

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