I considered posting this in the a/v forum but strictly it's not a vide (media) issue.

I have some classrooms here that have a Symposium display on them. It's an external display, with touchscreen, hooked to a video switcher. It can source video from an overhead or the computer, and send it to the projector. It also has a touchscreen interface via usb for the computer.

The new symposiums came in last fall, and the PC tech has been griefed a bit by them. Now it's my turn. I got repeated calls from rome where the display and projector were black. Power-cycling the symposium and display and playing with the display settings on the computer randomly would eventually suddenly fix the issue.

After some troubleshooting, I determined that the symposium requires 50hz (not 60, yes, we're in the usa...) to work. In most cases it auto detects correctly, but sometimes it fails when switching users at the login window.

I'd prefer to set up a little software agent on the computers to kick it back to 50hz if it gets set to 60 somehow, but I haven't been able to find a solution. The "cscreen" terminal app will get and set scan rate, but doesn't fully support additional external displays. (when mirroring from an iMac, it shows the scan rate is 0hz, the rate for the iMac, and doesn't show the 2nd display) I found the plist with the settings but it's got the scan rate buried under several dicts and arrays and is a huge pain to edit (and would not be effective without a logout) I also spent time exploring applescript, but it appears that there's no way to directly manipulate screen settings. (which is why cscreen was made, I think we can safely call this significant oversight on Apple's part) You can manipulate the system pref fairly easily, but I need something to run in the background.

Can anyone think of an option I missed? Or am I missing how to correctly use cscreen?


I work for the Department of Redundancy Department