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I'm unable to get my MacBook Pro to connect to my LG monitor via a KVM switch. A direct connection to the monitor works. The KVM does report the correct EDID information (as testing via Linux), but on OSX I can't see the display at all when connected this way.

macOS Sierra 10.12.15 DisplayPort->DVI Adapter (Apple) LG W2443T UNICLASS 4-Port DVI

I've used the command ioreg -lw0 -r -c "IODisplayConnect" to get information about the connected monitors. When connected directly I see both monitors. Via the KVM only one appears.

Is there some way to force the OS to find/use this external second monitor.

The KVM shows a connection to the MacBook (blinking light stops blinking). The keyboard/mouse connection work fine.

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The issue appears to be an incompatibility in the DVI Cable types. I was using a DVI-D dual link cable and swapped it out for a DVI-D Single link one. My monitor is connected to the KVM also with a DVI-D single link.

I presume somehow the MacBook was detecting dual link support, though the KVM does not support it I believe. By switching the cable I guess I forced the entire chain to be recognized as single link only.

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Are able to connect a different display to determine if the issue is with the capability with the Mac to the KVM switch or the display to the KVM switch. At the moment there are too many things it could be

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    Oddly it turns out to be the DVI cable I was using. Switching from a DVI-D Dual Link to a DVI-D Single Link corrects the problem. I don't know if this is because the cable was broken, or something in the chain doesn't actually support dual link. – edA-qa mort-ora-y Jul 17 '17 at 8:59
  • I'd say it was the wrong type of DVI cable. Had a similar issue with an Apple Cinema Display not working with a specific DVI adaptor because of the DVI type – Trent Jul 17 '17 at 9:03
  • Should probably post that as the answer if that worked for you – Trent Jul 18 '17 at 12:29

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