Connecting two Dell U2723QE Monitors to a MacBook Pro 2020

Physis2 wrote:

I have the MacBook Pro (13-inch, 2020, Four Thunderbolt 3 ports).

Your Mac can support two 4K monitors.

My MBP is connected to a CalDigit TS3. I am using genuine Thunderbolt cables. Besides trying to daisy chain the monitors, I've tried connecting through the CalDigit and also connecting direct connections from the monitors to the MBP. In both situations my MBP will have one screen and only one monitor will connect as a secondary monitor.

Daisy-chaining will not work – whether you daisy-chain them from a Mac host port, or from any of the ports on that Thunderbolt dock.

Based on the description of the Thunderbolt dock that Mr. Bennet-Alder provided, I believe that this would work:

• Run a DisplayPort-to-DisplayPort cable from the DisplayPort 1.2 port on the CalDigit TS3 Dock to one of your Dell U2723QE monitors. Use the DisplayPort IN port on the Dell monitor, not the daisy-chaining one. (I think that monitor ships with a plug covering the daisy-chaining one, but check the manual if you are not certain.)
• Run a USB-C to whatever cable from the Thunderbolt 3 daisy-chaining port on the CalDigit Dock to the other monitor. USB-C to {USB-C, DisplayPort, HDMI} would all work. USB-C to USB-C would have the advantages that (a) the cable comes in the Dell monitor box and (b) would hook up all of the downstream USB & Ethernet ports on that second monitor. Do not use the USB-C DATA ONLY ports on the CalDigit TS3 Dock; since while they would physically accept USB-C plugs, they do not provide a display signal.

If you wanted to use the downstream USB and Ethernet ports on the first monitor (the one hooked up using a DP to DP cable), you'd need to run a separate USB cable from the Mac or the CalDigit TS3 dock to it. I'm guessing that between the CalDigit dock and the downstream ports that you could get on the second monitor by using a USB-C to USB-C connection that you're not going to care about making a USB connection to the first monitor.

Physis2 wrote:

The connection via Thunderbolt cable to CalDigit TS3 is working which allows me to make the connection to the first terminal via the a DisplayPort Cable. This allows the 1st terminal to connect and be used as a secondary screen to my MacBook Pro.

The connection of the second terminal via a Thunderbolt cable which is connected from the 1st terminal to the second terminal is not working. It scans for a signal but says "No USB-C signal from your device".

If I understand what you are saying, you are trying to daisy-chain your monitors directly, using a USB-C to USB-C cable from a USB-C port on one monitor to a USB-C port on the other monitor. This will not work.

• The Dell U2723QE provides a DisplayPort (out) port for DIsplayPort MST daisy-chaining. This port is of no use when you are connecting Dell monitors to a Mac - directly, or indirectly, via a Thunderbolt dock. The Mac does not support DisplayPort MST daisy-chaining, whether you feed the first monitor with USB-C (DP) or with DP.
• The Dell U2723QE does not have any USB-C ports into which you can plug a second monitor. Only one of the three USB-C ports is for video at all, and it is for carrying video into that specific monitor.

You must connect both monitors to the Thunderbolt dock. In this case, the monitor that is connected via USB-C has to be connected via a USB-C cable from the Thunderbolt - downstream port on the dock, to the USB-C port (Video + Data) on the monitor. The other available USB-C ports on the dock and on monitor don't carry video.

You may also want to test that the second monitor is working correctly. If you move the USB-C plug that is currently plugged into the CalDigit TS3 Plus dock to a second USB-C / Thunderbolt port on the MacBook Pro – keeping the same cable, and keeping it plugged into the same place on the second monitor – does the monitor then display a signal? If it does, that might be an indication that something is not working right with the CalDigit dock and that you need to contact CalDigit. If it doesn't, then suspicion would fall on the monitor, the cable, or where you plugged the cable into the monitor.

You have not identified your MacBook Pro well enough for us to determine if it supports two external displays. Apple released three 13" MacBook Pros in 2020:

• MacBook Pro (13-inch, 2020, Two Thunderbolt 3 ports)
• MacBook Pro (13-inch, 2020, Four Thunderbolt 3 ports)
• MacBook Pro (13-inch, M1, 2020)

I believe that the two Intel models can drive two external 4K displays (like your Dell U2723QEs). The M1 model can only drive one.

None of these Macs support daisy-chaining a display to a USB-C (DisplayPort) display. Forget about that U2723QE feature. If you have one of the Intel-based MBPs that supports two displays, you will have to

• Connect each display to a separate port on the MBP, or
• Use a Thunderbolt (not plain USB-C) hub or dock to connect the displays. A Thunderbolt 3 link has a wider data pathway than a USB-C (DisplayPort) one, so the Mac will be willing to drive two 4K displays in this configuration.

Physis2 wrote:

Can I connect two Dell U2723QE Monitors to a MacBook Pro 2020? I am daisy chaining the two monitors together using the Displayport cable supplied by Dell plugged into the 90W DP port of each monitor but the second monitor is black. The first monitor connects and works but the second "Slave" monitor doesn't. Is the MacBook Pro 2020 not capable of supporting two monitors?

Daisy chaining displays on the Mac requires a connection to a genuine Thunderbolt device first display or dock using a genuine Thunderbolt cable...

connect a Thunderbolt dock to the Mac then plug two displays (can be non-Thunderbolt displays)

OWC, SonnetTech, and CalDigit all sell thunderbolt docks

ex

https://eshop.macsales.com/search/?filter.catidpath=3683/3684

<< I connected the the USB -C cable from the CalDigit (Thunderbolt 3 -Host) to my MBP. >>

Not good enough. That connection requires a genuine certified ThunderBolt cable with the Thunderbolt symbol on the cable.

As has been mentioned in passing, ThunderBolt cables have Double the data pathways of USB-C cables, and that is what is required to carry the data for TWO displays at once.

Physis2 wrote:

I have the MacBook Pro (13-inch, 2020, Four Thunderbolt 3 ports).

MacBook Pro (13-inch, 2020, Four Thunderbolt 3 ports) - Technical Specifications - Apple Support

Simultaneously supports full native resolution on the built-in display at millions of colors and: 

• One external 6K display with 6016-by-3384 resolution at 60Hz at over a billion colors, or
• One external 5K display with 5120-by-2880 resolution at 60Hz at over a billion colors, or
• Up to two external 4K displays with 4096-by-2304 resolution at 60Hz at millions of colors

Wild guess: Maybe to run both monitors, you will have to run each in

• Native 3840x2160 mode, or
• Retina "UI looks like 1920x1080" mode (or lower)

Someone with a M3 MacBook Air and two 4K monitors reported that they weren't able to use one of the Retina scaling modes above "UI looks like 2560x1440" with their second ("lid closed", "up to 5K") monitor. My guess was that the "up to" resolution applied to the internal drawing canvas – which, in any Retina scaling mode, has twice as many pixels in each direction as the "UI looks like" figure / Displays Settings "resolution".

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Maybe if you set your first monitor to run in Retina "like 2560x1440" mode (which implies a 5K drawing canvas), the Mac allocates as many hardware GPU units to it as if you had attached a 27" Apple 5K Studio Display. Thus, the second monitor gets no signal because there aren't any hardware GPU units available to send one.

Change the resolution to 3840x2160, or Retina "like 1920x1080" (either of which result in a 3840x2160 canvas), and now you're back within the limits that would let you attach two monitors. (Though granted, neither of these settings would be ideal in terms of text size for a 27" monitor.)

Might be worth experimenting to see if this is what is going on.

You could also check the MST settings in the monitors' Display menus and make sure that MST is turned off.

Other than that, I'm about out of ideas.

CalDigit – TS3 Plus

From the FAQ:

"To connect dual monitors connect one monitor to the DisplayPort connector and one monitor to the spare Thunderbolt 3 Type-C port using a USB-C Video Adapter."

"Yes, you can directly connect a Thunderbolt or USB-C Type-C monitor to the spare Thunderbolt 3 ports on the TS3 Plus. Please note that the USB-C ports on the TS3 Plus are for data only."

Physis2 wrote:

I purchased another Apple genuine certified Thunderbolt cable and it still doesn't work. What am I doing wrong?

It sounds like you are using the following configuration:

• Apple genuine certified Thunderbolt cable from a Thunderbolt port on MacBook Pro (13-inch, 2020, Four Thunderbolt 3 ports) to the Thunderbolt - Host port on the CalDigit TS3 Plus dock.
• DisplayPort to DisplayPort cable from CalDigit TS3 Plus dock to DP-in port on first Dell U2723QE monitor.
• A USB-C to USB-C cable that came with one of the monitors from the Thunderbolt 3 - Downstream port on the CalDigit TS3 Plus dock to the second Dell U2723QE monitor.

Is this correct?

It also sounds like you are not getting a signal on the second Dell U2723QE monitor.

Is that correct?

If so, here are some suggested troubleshooting steps:

• Check that the USB-C cable is plugged into the USB-C (Video + Data) port (Port 5) of the second Dell monitor, and not into the USB-C (Upstream) port (Port 8) or the USB-C (Downstream) port (Port 15). The Video + Data port would be the one that is closest to where you plug in the AC power cord, according to the manual.
• Check that the USB-C cable is plugged into the Thunderbolt 3 - Downstream port on the CalDigit TS3 Plus, not on one of the dock's downstream USB-C data-only ports.
• Check that the Dell monitor is looking for video input on USB-C. (Use the on-monitor menu controls.)

If all of these fail, try using a DIFFERENT cable to connect the CalDigit TS3 Plus dock to the second Dell monitor. E.g., set aside the cable you are using now, and substitute the identical USB-C to USB-C cable that came with the other monitor. Or substitute the first Thunderbolt 3 cable that you were using to connect the Mac to the dock. If one of the USB-C to USB-C cables that came with your Dell monitors was defective, substituting another cable might bring the second monitor to life.

Physis2 wrote:

I have already confirmed that the second monitor connects individually when I disconnect the first monitor and connect to the second alone.

You might want to try the following tests.

Single-monitor setup – does the Thunderbolt - Downstream port on the dock seem to work with video at all?

• Plug CalDigit dock into MacBook Pro.
• Plug first monitor into Thunderbolt 3 - Downstream port on CalDigit dock using a USB-C to USB-C cable.
• Leave second monitor unconnected.

Two-monitor setup – can you get two monitors working if only one is attached through the dock?

• Plug CalDigit dock into MacBook Pro.
• Plug first monitor into DisplayPort on CalDigit dock using a DisplayPort to DisplayPort cable.
• Plug second monitor into the other side of the MacBook Pro using a USB-C to USB-C cable.

if the second configuration works, and the first doesn't, you may want to contact CalDIgit to find out what is going on with being able to attach USB-C (DIsplayPort) monitors or adapters to that Thunderbolt daisy-chaining port.

Your Mac appears capable of supporting two displays, even two displays over one genuine Thunderbolt cable.

CalDigit TS3 plus:

Interface 

2 x Thunderbolt™ 3 [one connected to Host]

1 x DisplayPort 1.2

5 x USB-A 3.1 Gen 1 (5Gb/s, 1.5A, 7.5W)

2 x USB-C

    1 x USB-C 3.1 Gen 2 (10Gb/s, 1.5A, 7.5W) Rear -- DATA ONLY, no display support

    1 x USB-C 3.1 Gen 1 ( 5Gb/s, 1.5A, 7.5W) Front -- DATA ONLY, no display support

1 x SD Card Reader (SD 4.0 UHS-II)

1 x Digital Optical Audio (S/PDIF)

1 x Gigabit Ethernet

1 x Analog Audio In (Stereo)

1 x Analog Audio Out (Stereo)

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Dell U2723QE

Native Resolution

4K 3840 x 2160 at 60 Hz

Interfaces

• HDMI (HDCP 2.2)
• DisplayPort 1.4
• DisplayPort output
• USB-C 3.2 Gen 2 upstream

>> so please describe what cables and adapters you are using, though which ports, to make these connections.

Try unplugging the dock from the MBP and connecting both monitors to the MBP with USB-C to USB-C cables.

it would be interesting to know if removing the dock from the equation changes the results.

¿Does the problem follow one of the ThunderBolt cables, or does either ThunderBolt cable work fine?

The approved spec for Thunderbolt cables limits their length to 0.8 meters for Apple thunderbolt cables, 0.5 meters for other brands and high resolutions.