Singers Monitors Driving Me Mad

[Karanight]

Odd one here. I do a venue that's just had a refurb and since I've rebuilt my system there I've had problems with the monitor I use as the KJ and one of the monitors I use for the singers.
I use a Mac Mini and it has two outputs for the monitors. One is HDMI and I think the other is called a mini DVI.
I use a converter that has a VGA input and a VGA output and also a phono output which means I can feed one of the TV's in the venue using the phono as well as a computer monitor via the VGA
When I set everything up it works fine, I use the HDMI the feed the KJ's monitor and the mini DVI the feed the singers screens, all the monitors show what they should show but when I turn the computer off and then on again the computer monitor doesn't show anything whilst the TV does. I've found the only way the get the computer monitors to work again is to swap the leads about on the Mac Mini so I have the HDMI now feeding the singers monitors and the mini DVI feeds the KJ's monitor, I still get no signal so I swap the leads back and only then does it work.
This happens every time I turn the system on, has anyone any ideas whats going on

[dave]

try just doing "detect displays" (displays pref panel)

[Karanight]

Tried that and got no result. I've not seen anything like this before and it's driving me nuts

[dave]

sorry dude, sounds strange. i guess i'd have to be there to help diagnose it.

[DeusExMachina]

Okay, much of this makes no sense, so you are going to have to clarify.
First AFAIK, no Mac Mini had both HDMI and DVI, so you probably have a mid-2010 Mac Mini with HDMI and miniDiplayPort.
From that, it is impossible that you can "swap the leads about on the Mac Mini", as one port is HDMI, and the other is mDP. So I am guessing that you mean "swap the VGA cables between the adaptors".
Your description of which signal is surviving the restart is unclear, but I assume that it is the mDP signal.
The first thing to do is to restart with JUST the primary monitor powered on. This should result in the kJ screen correctly displaying, and then power on the other monitor.
If that is not successful, you may be helped by resetting PRAM. Restart, and hold in the ⌘ ⌥ P and R keys IMMEDIATELY, BEFORE the gray screen or system POST chime.
Keep holding the keys.
The screen will go black again, and you will hear the POST chime a second time.
Release the keys and continue booting.

[dave]

also, "Detect Displays" is now invisible in Mavericks. Hold the option/alt key to see it.

[Karanight]

It was the VGA leads that I swapped.
The problem seems to have been related to KVM switch that was in use at the venue. I've since removed the KVM switch and put another monitor in and everythings working OK now. The reason the KVM switch was there is the venue has their own system for playing music during the week and they simply switched to their computer

[DeusExMachina]

The intervening KVM prevents the Mac from seeing the monitor switch, because it is reporting to the Mac that IT is connected, so the Mac never sees the change.

[dave]