HDMI QHD resolution trouble

I don’t like HDMI for computer output, it’s had more problems than DisplayPort, but I’m working with what I have. Does anyone have experience with solving issues with HDMI and QHD monitors?

I have a new 27" HP Z27n G2 monitor and I’m having trouble getting its native resolution (2560x1440) on one of my Macs via my desired connection path.

When I connect this way: 16-inch MacBook Pro, TS2-to-TS2 adapter, TS2 cable, CalDigit Thunderbolt Station, HDMI cable, Z27n G2, the best resolution I can get is 1920x1080. If I instead use an Apple USB-C HDMI adapter, I get the native resolution. This monitor replaced an old 24" Dell Ultrasharp that was 1920x1200 over the same connection path.

The Thunderbolt Station is supposed to handle up to 2560x1600 so I was going to write to CalDigit but first decided to try connecting it to a 13-inch Late 2013 MacBook Pro. Connected to the 13" MBP, I get the monitor’s native resolution!

I don’t see how the TS3-to-TS2 adapter could be the source of the problem but I don’t have another another adapter or cable to test. Just because I had them, I did try a different HDMI cable (no difference), and a 3rd party USB-C HDMI adapter (like the Apple one, it supports the monitor’s native resolution).

On the surface, it sounds like your docking station is the problem. Maybe it isn’t reporting the display’s capabilities back to your Mac correctly? Is there a device driver that needs to be installed?

I suppose macOS may be making an (unwarranted) assumption that TB2 doesn’t have enough bandwidth for your resolution, but that would surprise me.

I’ve read that other people have had luck using a tool like SwitchResX (shareware, 10-day trial period, $16 per computer registration) to force resolutions that macOS doesn’t think your monitor supports. It might be worth giving it a try.

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Yes, even though the I get full resolution when the dock is connected to the Late 2013 MBP, there’s probably something not quite right about the dock that the 2019 MBP doesn’t like.

I tried SwitchResX and it could set 2560x1440 but it looked fuzzy, like it was being scaled, even though the monitor said it was receiving that resolution.

I received a Mini DisplayPort to DisplayPort cable meant for the Late 2013. If I use that cable on the dock’s other TB2 port, I get full resolution. I want to be able to have both laptops connected to the monitor at the same time but it only has one DisplayPort in so this isn’t a long-term solution. I’ll probably give up on the dock for video.

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This is important. It means that the Mac can support the display.

As for why the dock doesn’t support the display, I’m not yet sure, but I suspect it is out of spec.

According to HP’s product page this display only supports 2560x1440 at 60 or 75Hz refresh.

Looking at a table of HDMI capabilities, this requires HDMI version 1.3 or later. HDMI 1.2 only supports that resolution at 30 Hz, which your monitor doesn’t support.

Unfortunately, CalDigit’s product page and user manual don’t say what version of HDMI the device supports, but I’m guessing that it is HDMI 1.2. Later model CalDigit docks advertise HDMI 1.4 or 2.0. This one is from a time where nobody considered it important to advertise the version, which usually means 1.0, 1.1 or 1.2. 1.2 is the only one of these capable of supporting 2560x1440 at all. I also suspect that if they supported HDMI 1.3 or 1.4, they would be advertising 4K support (since those versions support 4K at 30 Hz refresh).

It might be interesting to see if your can use SwitchResX to generate 2460x1440 at 30 Hz to see if you can get the HDMI port to put out that resolution. It may not work, because the monitor’s spec sheet says it won’t, but it might be worth a try anyway. But even if it does work, I don’t think you’d be satisfied with a 30 Hz refresh rate - better to stick with the DisplayPort interface.

Since you need two DisplayPort interfaces but only have one on the monitor, perhaps a DP-HDMI adapter (one capable of 4K - meaning at least HDMI 2.0) can solve the problem. An Amazon search reveals many different such devices, including this one. (I don’t have personal experience with it, but it’s from a respected brand and claims to do what you need.)


I already knew the Mac can support the display because I got full resolution with two different USB-C HDMI adapters (plus, it’s a 2019 MacBook Pro). I already know the dock’s HDMI port can output the monitor’s full resolution because it did when it was connected to the 2013 MacBook Pro and when I used SwitchResX on the newer Mac (but the image with SwitchResX was fuzzy). I didn’t note the frequency on the older Mac but from SwitchResX it was 60Hz (well, 59.8-something).

I don’t want to use the dock’s Thunderbolt for Mini DisplayPort video output because I use the port for my iSight camera. Basically, I’ve given up on the dock for video output, I’m using an Apple USB-C HDMI adapter instead; I have the power cable connected to the adapter’s USB-C pass-through so the number of used ports on the Mac hasn’t increased. The only reason I’m still using the dock is for conveniently located USB Type A ports.