Plugable DP-HDMI

Sometimes its the little pieces of tech that cause us the largest headaches, but sometimes they are also what gives us faith in vendors and how they treat customers after the sale has been completed. Purchasing a simple converter dongle turned out to be a lesson in both (with a happy ending).

Purpose

At time of writing, getting a consumer GPU is a difficult affair, especially if you are after a new RTX3080 and don't want to sell a kidney for it. While this presents a challenge, workstation GPUs were still readily available (and at a decent price) prior to the card shortage. These workstation cards (specifically the nVidia Quadro line) also have the advantage that they can be passed through to a virtual machine without the dreaded 'Code 43' issue (though nVidia has removed this limitation making things significantly easier). One wrinkle with using a Quadro GPU is that they come with DisplayPort connectivity and not HDMI (not ideal when connecting to a TV). This is solved (for the most part) by using a converter dongle, though it does bring some limitations.

Originally (back in early 2020) I purchased a cheap DisplayPort-to-HDMI adapter which in honesty was a worthless piece of trash unfit for a rubbish dump. This no-brand dongle wouldn't achieve half of the resolutions advertised, not to mention continuously cut out (even on a 1m cable for testing). A bit of research later and a Plugable DP-HDMI dongle was purchased (revision 2 at the time), which achieved 4k@60Hz without any issues. This dongle worked from day 1 (even with a 10m active HDMI cable) and allowed me to play games with no real issue. As technology improved however, support for HDR was added to a newer version of the dongle, and as my TV supports HDR it makes sense to upgrade and take advantage of it. With a cable running to an upstairs TV I figured the original dongle could be used to connect to that as well, allowing me to play games either downstairs or upstairs as needed.

Problems

Alas, with all new technology there are always quirks and unexpected behaviour. Once my new dongle had arrived it was connected however an immediate problem became obvious, the original 4k@60Hz no longer worked. The TV screen would flicker on and off every 2 seconds without fail, with no indication as to what was going wrong. To make matters worse, this wasn't with HDR either. Testing at lower resolutions worked, as did dropping the refresh rate to 30Hz, however fast-moving games really don't work well when set to this and its not a workaround I wanted to implement. Checking the cable specs showed that there shouldn't be an issue (and with the older dongle it did work without issue), so it was time to troubleshoot.

Plugable has a nice debug tool that can be downloaded and collects information from the system to see how things are configured/what version of the GPU drivers are present/what display is connected etc. Troubleshooting continued, trying to determine what was causing the issue. TV firmware was checked (to ensure its on the latest revision), but still no joy. Credit to Plugable at this point as a replacement dongle was sent to me (in under 24 hours, seriously), though sadly even with the new dongle the same issue persisted. After ruling everything out, the only remaining piece was the active HDMI cable being used.

As it turns out, the cable was the issue, as the current draw from the repeater in the HDMI cable was just a little too high for the newer dongle when running at its maximum resolution/refresh rate which resulted in the repeater component restarting over and over (it wasn't the DP-HDMI converter chip restarting, this was validated). Taking the plunge on a fiber-optic HDMI cable (which uses a separate in-line USB power connector resolved the issue there and then, with a stable 4k@60Hz even with HDR enabled. In hindsight, purchasing an active (copper) HDMI cable in the first place wasn't the best idea, but at the time it made sense. The replacement fiber-optic HDMI cable has the advantage that it supports HDMI2.1, enabling 4k@120Hz (which I shall be upgrading to at a later date).

Support

As the title of this post may have given hint to, the support throughout this process was brilliant. From the first email sent to the Plugable support, they were friendly, patient, very quick to respond, clear on the next steps, and even sent me a replacement dongle just in case mine was faulty given the behaviour being observed. Considering the lack of response I got for my wireless CarPlay dongle (which cost a ridiculous amount and is still so broken it isn't funny), having this level of service for a cheaper device goes to show that great service is possible and doesn't cost the earth. In all of my years working in IT and all of my experiences both inside and outside of work, this sits in the top 5 for best received.

Future

Right now the dongle is working great and its stable after hours of testing. It will continue to be used for the foreseeable, and hopefully once HDMI2.1 is more widely adopted (and someone creates a converter chipset for it) I hope Plugable will make a dongle to achieve 4k@120Hz with HDR (for newer GPUs that support it). They are also on my preferred vendor list for other tech as it gets released :-)