Old Samsung monitor S24D590L DP to HDMI connection does not work all of the time

I have a Macbook Pro laptop that I use to connect to a TBT3-UD1-83 device that then connects to a S24D590L monitor’s HDMI port via the DisplayPort to HDMI converter dongle that came with the Plugable TBT3-UD1-83 unit.

Sometimes when I connect it both the Plugable device and the LG monitor at the same time (i.e., when I return home with my computer) the Samsung display is blank.

To get it to work I sometimes have to disconnect my other monitor which is directly connected to my computer (LG UltraFine 5K Display) which then enables the Samsung monitor and then reconnect the LG monitor. Once I do that, it works.

Any way to debug this or should I just keep doing the whole disconnect-the-other-monitor-first method?

Hello and thank you for posting!

Thank you as well for the detail you provided and the troubleshooting that you have already performed that is much appreciated.

While I cannot be sure based on the detail provided, the fact that your LG display is a 5K resolution display could be a possible contributor.

To expand further, different model Apple MacBook Pro laptops have different capabilities in terms of both the maximum number and maximum resolution of external displays they can support. This is ultimately determined by the specifications of the laptop’s internal graphics adapter.

To help determine if this may be the pertinent factor here, can you please let me know the specific model MacBook Pro you are using? For example, a MacBook Pro 13-inch 2019 model laptop with two Thunderbolt ports.

If you are unsure which specific model you are using, you can access this information by selecting the Apple Menu --> About this Mac

Thank you for giving us the chance to help!

Plugable Technologies

MacBook Pro (16-inch, 2019) - 2.6 GHz 6-Core Intel Core i7 - AMD Radeon Pro 5300M 4 GB - Intel UHD Graphics 630 1536 MB.

Thank you for getting back to us with the additional information!

My original theory was that you had a 13-inch model laptop with an Intel graphics adapter only,

Intel graphics adapters in the MacBook Pro can only support one display at 5K resolution, so the timing of the connections of the displays could have been influencing the behavior.

To put that another way, if the 5K display was connected to the system first, then system would not have the capability to drive a second Samsung display. If the Samsung display with 1920x1080 resolution was connected first, when the LG 5K display was connected it may work but at a lower than maximum resolution.

Of course, since you mention your MacBook Pro is the 16-inch model that has both an Intel graphics adapter and an AMD graphics adapter (https://support.apple.com/kb/SP809?locale=en_US) that limitation does not apply here.

By any chance are you connecting the Plugable dock and the LG display to Thunderbolt 3 ports on the same side of your laptop? If that is in fact the case, if you connect the LG display to one side of the laptop and the Plugable dock to the opposite side of the laptop does that change the behavior?

I ask because there are two separate Thunderbolt controllers within your laptop. One controller is connected to the two Thunderbolt 3 ports on one side, and the other controller is connected to the two Thunderbolt 3 ports on the opposite side.

As a result, I am curious if ‘separating’ the devices across the two Thunderbolt controllers changes the behavior in any way.

Thank you,


Interesting. Yes, they were being connected on the same side of the laptop. I’ll let you know if that helps, albeit the problem isn’t happening right now (due to the nature of what I described in my earlier post) and doing the switch to the other ports is almost the same steps I’m taking to alleviate the problem (i.e., disconnect the LG monitor and then reconnect).

Thanks for the tip.

You are most welcome for the information!

Please just let us know the results as time allows, and we will determine the next steps from there.

Thank you,


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