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This is a interesting one. I use a KVM switch on my Mac Pro and Cinema Display. While the display is on another computer, the Mac switches to a different resolution (not seeing a monitor). I know it does while switching back to the Mac as my screen windows have changed places, to the lower half of my screen while the resolution is back to normal.

Does anybody know how to prevent this from happening. I've searched for "fixed screen resolution" etc. I've tried SwitchXres and Stay to no avail. (These apps do not work if there is no screen.)

It would be great if I could set the screen resolution to only one setting (the max) and that there are no other alternatives where the Mac could choose from.

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What model KVM? – Stu Wilson Mar 28 '12 at 20:03
It is a Starview SV231DPUA from My Windows 7 PC has no problems with this switch. – user20981 Mar 31 '12 at 10:47
The manufacturer's tech support got back to me last week, and I completely forgot about it. They say the KVM does not return any signal at all. However since the same Tech Support person told me my computer went into standby when I switched to a different one with a KVM, I'll take that with a pinch of salt. – Stu Wilson May 16 '12 at 18:16

This is in all probability down to the KVM providing a fake monitor signal to OS X whilst the monitor is not "connected" to the OS X box; providing the KVM model would confirm this.

Generally, KVM fall into three monitor modes, usually these are priced low to high:

  • No signal - where the non active connections receive no indication that a monitor is connected
  • Fake - where the KVM provides a signal to the host that indicates a monitor is connected
  • Pass through - where the KVM emulates or attempts to provide through another fashion, the signal of the monitor to all hosts

EDIT: I did test adding a monitor to a Mac Mini and the resolution it first went in on was low, even after setting up the resolution, disconnecting the monitor (power off at the wall and back on) only sometimes caused the resolution to default back to a very basic one.

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It's been a while,

I got rid of the KVM switch, I now remote control the other computer and don't have the problem anymore. The KVM switch has hit the road!

Thanks for helping to confirm this problem. I do not see any solution to this problem.


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