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philm · Sep 21, 2006, 05:21 PM

My wife has a MBP and was getting ready to deliver a lecture in my department today. The lecture theatre has a somewhat cobbled together AV system with a new data projector which has perhaps 8 metres of cable between it and the male VGA connector at the front of the room (via a 'splitter' box) to allow the permenent PC in the same room to also connect to the projector.

Interestingly, plugging in the MBP did not allow a successful connection to the projector. However, when I did the same thing with my 12" Powerbook it was OK (confirming that the cabliing was sound) and when we 'broke' into the long cable at the splitter box and connected up with the MBP again, it worked (confirming that the MBP/VGA adapter were OK).

Conclusion: the MBP has a problem with long video cables; if the MBP is not able to detect the projector across a long length of cable it cannot work. I know that this lecture theatre set up has been successfully used by dozens of speakers with various laptops over the years, so it is a MBP problem.

This is a problem which takes me back to the Powerbook 3400 days when you had to install a control strip module to 'force video' from the Mac. I fear that the days of AV technicians saying 'oh, no, not a Mac' might be with us again.

Can anyone share any similar situations?

ibook_steve · Sep 21, 2006, 07:53 PM

I seriously doubt the long cable is the problem. If it was, you'd get lousy looking video, not no video at all. When you plug the MBP past the splitter box, does anything happen? Screen flash? Listing of projector resolutions in the Displays preferences or menu? VGA is VGA so it should work. But I would need to know if the MBP is even detecting the projector.

Steve

philm · Sep 22, 2006, 04:14 AM

Originally Posted by ibook_steve

I seriously doubt the long cable is the problem. If it was, you'd get lousy looking video, not no video at all. When you plug the MBP past the splitter box, does anything happen? Screen flash? Listing of projector resolutions in the Displays preferences or menu? VGA is VGA so it should work. But I would need to know if the MBP is even detecting the projector.

Steve

THanks for this. When connecting, there is a screen flash (which I presume means that something is happening) but there is no list of projector resolutions (only the Color LCD list for the in-built screen) and then projector screen jumps back to its default blue format.

On a related matter, I notice that when I plyg in the VGA adapter to the MBP, the Mac's screen flashes, but there is no secondary list of monitor resolutions. In other words, it does not seems to 'detect' the adapter. This is different to the behaviour of (a) doing the same thing with the TV/S-video adapter in the MBP and (b) using a VGA adapter with the Powerbook 12". This seems a bit odd to me, but reading various web-sites, this might be the correcter behaviour.

Simon · Sep 22, 2006, 04:40 AM

Have you tried attaching the adapter to the VGA cable first and as a last step connecting the adapter to the MBP? Any difference?

Timetheus · Sep 22, 2006, 10:29 AM

I've used mine over a long cable without a problem. It was a similar set up with a 4-way switch and over a similarly long cable, I wonder, then, if it was problem between the projector and the MBP. Although, as philm said, "VGA is VGA" so that doesn't really make sense either.

philm · Sep 22, 2006, 04:17 PM

Originally Posted by Simon

Have you tried attaching the adapter to the VGA cable first and as a last step connecting the adapter to the MBP? Any difference?

I don't think we tried that actually. Am I right that the MBP does not appear to 'detect' the adapter unlike other Mac laptops and unlike the TV/S-video adapter?

ibook_steve · Sep 22, 2006, 08:14 PM

If you don't connect a monitor to it, the VGA adaptor does not do any detection. The TV adaptor tricks the machine into thinking a monitor is attached because TVs do not have any extra signals for sending a detect. Do what Simon says. (hee hee)

Steve

Simon · Sep 23, 2006, 04:15 AM

Originally Posted by ibook_steve

Do what Simon says. (hee hee)

I sooo saw that one coming.

tooki · Sep 23, 2006, 11:10 AM

Originally Posted by Simon

Have you tried attaching the adapter to the VGA cable first and as a last step connecting the adapter to the MBP? Any difference?

Quite right. The connection order is essential for auto-detection. (Though if you do connect in the wrong order, you can select "Detect Displays" on the Mac afterwards.)

I agree that it's unlikely that the cable length is the problem. Either something in the setup process isn't right, or the switchbox isn't passing through the DDC2 control signals, preventing the Mac from correctly identifying the display mode.

tooki

philm · Sep 23, 2006, 12:23 PM

Originally Posted by tooki

Quite right. The connection order is essential for auto-detection. (Though if you do connect in the wrong order, you can select "Detect Displays" on the Mac afterwards.)

I agree that it's unlikely that the cable length is the problem. Either something in the setup process isn't right, or the switchbox isn't passing through the DDC2 control signals, preventing the Mac from correctly identifying the display mode.

tooki

As I outlined in my original post, all works fine with my 12" Powerbook but not with the MBP, yet the MBP works with other projector set-ups. Although the cable length seems an unlikely explanation, it's all I am left with! Perhaps this thread will assist people who may have similar problems in the future.

Rodyeast · Nov 1, 2006, 02:00 AM

I had the very unfortunate experience of not being able to get my brand new MBP to work for a presentation that I was making today. My 2.33 MHz duo didn't work. A non-Intel MBP worked fine. I am desperate for advise as to how to fix this problem as I am leaving for a two week speaking tour on Thursday evening and I want to take my new machine.

This is highly frustrating as my previous PowerBook always worked and I was a total braggart about Mac's and LCD projectors!

By the way, detect displays did nothing except get a brief fuzzy signal that disappeared quickly.

ibook_steve · Nov 1, 2006, 02:46 AM

What resolution were you trying to use with the projector? Did you try multiple resolutions?

Steve

P.S. There's no such thing as a non-Intel MBP.

Simon · Nov 1, 2006, 07:19 AM

Originally Posted by Rodyeast

By the way, detect displays did nothing except get a brief fuzzy signal that disappeared quickly.

• Remove all dongles, cables, etc.
• Select detect displays
• Attach the VGA cable to the dongle
• Make sure the projector is on
• Attach the dongle to the DVI port
• Select detect displays

Has never failed me. Not on a PB, not on a MB, not on a MBP.

Rodyeast · Nov 1, 2006, 02:50 PM

Originally Posted by Simon

• Remove all dongles, cables, etc.
• Select detect displays
• Attach the VGA cable to the dongle
• Make sure the projector is on
• Attach the dongle to the DVI port
• Select detect displays

Has never failed me. Not on a PB, not on a MB, not on a MBP.

Do detect displays twice?

Thanks and I'll let you know what happens.

By the way, this morning, I very successfully connected to the LCD projector here at work. I was able to futz with the with the display settings and I put in 1024 x 768, 75 Hz. Does that sound like a good "general" setting for it to remember?

Rodyeast · Nov 1, 2006, 03:13 PM

Originally Posted by ibook_steve

What resolution were you trying to use with the projector? Did you try multiple resolutions?

Steve

P.S. There's no such thing as a non-Intel MBP.

I tried 1024 x 768 and 800 x 600 - no luck. See my response to Simon for more info.

Sorry about the non-Intel comment. I guess I meant the most recent PowerBook before the MBPs. It did look very similar.

Frugle · Nov 1, 2006, 03:19 PM

I've never had a problem connecting my my MBP to a 25 foot run, it has to be the way they are talking. Your sure you have your MBP to run as either a secondary display or a clone right? your running <1024x768? and like they said above, <75hz?

It sounds like it is seeing it, but not assigning it as a display.

Simon · Nov 1, 2006, 03:20 PM

Originally Posted by Rodyeast

Do detect displays twice?

No, not in general. I just suggested doing so in your case to get you to a fresh slate. You might have chosen the wrong order to connect stuff. Steps 1 and 2 are not necessary every time, it was just a recovery precaution.

LfGrdMike · Nov 1, 2006, 03:31 PM

You could also try to delete your displays plist file and run Onyx to delete caches. Its amazing the number of times clearing the caches has solved goofy problems.

Its worth a shot.