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Old 08-09-2022, 10:10 AM   #1
WMTaylor3
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Unhappy Multi-dock causes pulsing/flashing on darker screens

Hi all,

I'm new to the forums but my name is William Taylor and I'm the (mostly) happy owner of a Targus Dock 570 and a Targus Dock 190. I say mostly as, as the title suggests, I'm being plagued by an odd flickering of sorts.

Context:
My setup consists of 6 monitors, arranged in a 3-wide by 2-high configuration. All but the bottom middle display are 2560x1440 monitors running at their native resolution, the remaining one is a 4K Samsung monitor running at a non-native 2560x1440 in order to match the others.
The docks are connected to an HP EliteBook via USB-C. The 570 connects directly to the laptop and drives the bottom row of screens, and the middle one on the top row. The 190 is driving the remaining two flanking monitors on the upper row and is daisy-chained from the 570.

The problem:
Primarily on the center monitor, though it occurs to a less noticeable extent (I think due to the brightness and contrast settings on the center monitor making it more evident) there is a distinct pulsing/flickering sensation on darker applications, such as Visual Studio Code in dark theme. It's difficult to describe, the image itself never cuts in and out, but it frequently changes in darkness/black level, almost as if it's trying to decide between two different black level/gamma levels. This can happen to the screen over all, or just in sections of it, i.e. the bottom third of the screen or the left fifth flickering/pulsing between darkness levels. This is made particularly evident when there is activity on another monitor. It's not a 100% reliable way to reproduce the effect but when dragging windows around or opening a new file/folder it seems to cause the center monitor to have a freak out. Playing a video or some kind of motion clip on one of the other monitor also serves as a pretty reliable way to reproduce it.

What I've tried (unsuccessfully):
  • Reconnecting the 190 directly to the laptop via another USB port (issue still occurs).
  • Connecting another laptop to the docking station (issue still occurs, suggesting it's not the laptops fault).
  • Reconnecting the bottom center monitor (where it's most evident) to the dock 190 (issue still occurs, suggesting it isn't just the 570's fault. Besides, the issue also shows up on the screens driven by the 190 even when it is connected to the 570, so I don't think it's either of the docks being faulty).
  • Connecting all 6 monitors to my desktop PC directly (PC has two GTX 1070s), bypassing the dock setup (issue disappears and the screens work perfectly, suggesting the screens themselves aren't faulty.)
  • Changing resolution, refresh rate etc on the monitors, yielded no results so I've put them back to 60Hz each.

What I've tried (almost successfully):
  • Physically disconnecting the secondary dock (the 190) from the setup entirely, leaving only the 570 driving it's 4 displays (issue still occurs when playing back video footage, but it's almost disappeared otherwise. That's good enough for me but I would like the two remaining displays back).
  • The same as above, but disabling the displays in Windows display preferences. Again, leaving only the 570 displays (results in the same outcome as above, essentially fixed but leaving me without two of my displays).

The closest I've come to success is to have the displays driven by the second dock disabled, either by unplugging the second dock physically or by disabling the connected displays in Windows display settings. Doing so causes the issue to almost entirely disappear. Not entirely, but largely, enough to live with at least.
If it were a case of the docks being daisy-chained I could understand, but if that's all it was, I would expect the issue to resolve when connecting both docks directly to separate USB ports on the laptop. (Note I don't think it's a USB controller issue either, as when I connected them both directly, they were on different sides of the laptop, one to a USB-C port and the other to a USB-A 3.x port. I believe they are on separate USB controllers/internal hubs etc.).

Theory:
The issue occurs only when connected to the displays via the docks. Direct connection to the monitors from my desktop is fine, so it isn't the monitors.
The issue occurs across multiple different DisplayLink docks of both the same and different models. So it isn't a case of a faulty unit.
The issue occurs the same across multiple laptops, provided both docks are connected. So it isn't the laptop.
The issue occurs the same whether the docks are daisy chained to the laptop or each with their own direct connection, so it isn't a topology issue.
The issue mostly (though not entirely) disappears when the second docks displays are disconnected, either via hardware or via software, so it isn't something physical like a grounding loop.
...
Thus the only thing I can think of is something in the DisplayLink drivers that have resulted in them not being happy when attempting to run two docks (maybe of different types/DisplayLink chips) off of one laptop. Hence why I'm posting here, you guys are the experts.

Additional notes:
I'm actually on my second Dock 570, the first having been replaced by Targus under warranty for having a faulty power supply, the interesting thing is, this issue has been present on both 570's as well as the 190 so I don't think it's a case of a faulty unit. On that note, Targus support has been AMAZING and I highly recommend them.

System specs:
HP EliteBook 840 G8.
i5-1145G7.
32GB RAM.
Intel Iris Xe graphics.
Windows 10 Pro Version 10.0.19044.
DisplayLink driver version 10.2.7042.0.
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Old 08-10-2022, 06:30 AM   #2
WMTaylor3
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Update to this.
I've attempted (temporarily) swapping the 190 out with a Dell D3100. It's unable to drive the two monitors it is responsible for at 1440p, however even running them at 1080p the flashing/flickering issue still presents.

Interestingly I can reliably reproduce it by opening dark theme VS Code on the bottom center monitor, opening DisplayLink Manager on top of it (as a small window), then selecting one of the displays within DL Manager, selecting the resolution drop down and scrolling up and down the list with my mouse scroll. I don't have to select any of the options, the act of scrolling is enough to trigger it.

Something about the display updating/refreshing seems to cause the problem to appear.

Further testing using the drop-down scroll method listed above has shown the issue still occuring even when both the 190 and the 3100 are disconnected, leaving only the 570. This suggests it may not have anything to do with the multi-dock setup and it could just be a side effect of how DisplayLink is refreshing the display?
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Old 08-12-2022, 11:05 AM   #3
KatarzynaKowalczyk
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Hello,

We would like to take a look at the logfiles and see what our driver reports so if you do not mind please gather those and you can respond to this message with the logfiles attached or send them to our support team directly to: technical-enquiries@synaptics.com

Instructions on how to gather the logfiles are available here.
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