Solved: Dell E-Port port replicator DVI support

This is the third in a series of posts on hard-to-find information about the Dell Precision M4800 laptop. The topic is about DVI support for the Dell E-Port and E-Port Plus port replicators.

For some brief context, I upgraded from a 1680x1050 monitor (Dell E228WFP) to a 2560x1440 monitor (Benq BL3200PT), and was having trouble using the new monitor at native resolution. Using two laptops (Dell Precision M4800 and Dell Latitude 6520) with two port replicators (E-Port T308D, A03 revision; E-Port Plus 12TFY, A01 revision), I could achieve native resolution when connected via DisplayPort, but not via DVI.

Ultimately, from talking with Dell and Benq technical support, we determined that the issue was that the Dell E-Port and E-Port Plus port replicators only support single-link DVI. My evidence for this is as follows:

• The Dell Knowledge Base article LCD display and multiple LCD display frequently asked questions (FAQs) (http://www.dell.com/support/Article/us/en/19/QNA43649/EN) states the following:

"E-Port docks have Dual Link DVI connectors to allow all DVI cable types but are wired for Single link DVI resolution, and cannot be used for DVI connections requiring Dual Link DVI resolutions above 1920 x 1200."​

Note the difference between the shape of the DVI connector on the E-Port units, which has holes for dual-link cables, and the wiring on those connectors, which is only single-link.​

• From testing all four combinations of the two Dell laptops with two Dell port replicators cited above, I was unable to achieve a stable (*see below) connection to the display at 2560x1440 resolution using a DVI dual-link cable. When using the same cable to connect the same monitor to my desktop computer (using either of two different video cards), I could use the display's full native resolution.

• The Dell product pages for similar E-Port and E-Port Plus models to the ones that I tested state that the DVI port(s) is single-link. For example, check the Tech Specs tab on the page for the GNPHP model (http://accessories.dell.com/sna/productdetail.aspx?c=us&l=en&s=bsd&cs=04&sku=331-6304):

"2 x display / video - DVI-Digital - 18 pin digital DVI (Single-Link)"​

This all seems fairly obvious in retrospect. In case anyone digs into this in detail in the future, there are some other things you should know.

• Dell has many... versions?... of the E-Port and E-Port Plus port replicators, each with a different part number
  • I was not able to find product pages (for sales or support) for either of the units that I have, which is why I contacted Dell technical support for confirmation about their capabilities
  • For the port replicators with product pages, each lists the specific computer models that it does support. I can't say this authoritatively, but from working with my own systems and from reading other posts on various forums, it appears that any computer that can connect to an E-Port style dock can connect to any E-Port style dock, even if it's not specifically listed as supported.

• When connected to the BL3200PT monitor using DVI from either of the port replicators, my Windows 7 laptops detect the monitor as either supporting 1920x1080 or 1280x720 natively (both of which are incorrect). On both machines / port replicators, I've been able to force them to run at 2560x1440 using the DVI ports on the port replicators by fiddling with the NVIDIA Control Panel application (Display > Change resolution > Customize). The results have been unstable, though, yielding either screen artifacts, flickering screen, or blank screen, seemingly intermittently. Sometimes I can get a day or two's worth of use at full resolution over DVI, but it ultimately fails.

• Using the E-Port DisplayPort connector instead of DVI works normally at full resolution. Unfortunately:
  • Windows 7 seems to think that I've physically disconnected my monitor every time I turn the power off. This is apparently a well-known problem with Windows and DisplayPort (I'm still looking into the details, with the help of Benq technical support). The problem does not occur when connecting the same computer to the same monitor over DVI.
    
  • I happen to have a very nice DVI KVM switch that I'd like to keep using; the equivalent DisplayPort version of this switch is over $600 USD

Lastly, any of the above is subject to change in the future. Hopefully Dell will make a version of the E-Port / E-Port Plus that can keep up with modern, professional DVI monitors (I've added a suggestion to their "ideas" website to add such support).

In the meantime, I'm contemplating purchasing an active DisplayPort-to-DVI dual-link adapter (also expensive; >$100 for the highest rated ones), or just continuing to press a series of buttons on my KVM switch and monitor each time I want to switch between computers. If anyone has a better suggestion, I'd appreciate your feedback.