Betalogue

I had a pretty interesting troubleshooting experience yesterday. My wife has been using my old 2006 Mac Pro in her store, with my old 23” Apple Cinema Display.

Now this is a display that I bought a long time ago, back in 2002 to be exact. Back then it was quite expensive (over $5,000 CDN before tax), but it was one of the best displays around, and certainly a great deal better than the monstrous Trinitron CRT monitor that I was using before then. There were significant worries about “dead pixels” in LCD displays back then, but my display was perfect in that regard. I used it for several years as my main monitor, until I replaced it with a 30” display. Then further down the road I got a second 30” display and the original 23” display was used as a backup monitor for a second computer I was using from time to time.

And that, in a nutshell, is how the display ended up being used in my wife’s store. It’s over 10 years old now, but it still has a very good picture. It might not match more recent models in terms of brightness, but for its current use it is excellent, and provides a decent amount of screen real estate (1920×1200). It still requires an ADC-to-DVI adapter, of course, but that adapter also seems to be working fine.

The one thing about this display, however, is that for a long time it has been having problems with its USB ports in the back. I can’t remember exactly when the problems started, but even if it was still when the display was under warranty, I never bothered to get it fixed, because it could be fairly easily worked around (simply by using different USB ports and a hub). The USB ports didn’t fail entirely, but they were definitely flaky.

In my wife’s store office, the USB ports in the back of the display are the most convenient connections for her keyboard and mouse, so that’s what she’s been using. It had been working OK for a year. At least there were no obvious problems with the keyboard or mouse. She did, however, have some weird problems when getting back to the machine in the morning, with the Mac Pro not waking up from sleep properly. I told her to use the Mac Pro’s power button and that worked OK as a workaround, so I didn’t investigate things any further.

Then yesterday, when she reopened the store for the Christmas after having been closed for a couple of months, and she tried to turn the Mac Pro on, all she got was a grey screen. She got the startup chime, but after the screen turned grey, nothing would happen. Several attempted restarts failed to make a difference. Unplugging the computer and plugging it back in didn’t help either. I tried swapping the two internal hard drives. I tried plugging the keyboard and mouse directly into the computer. I tried holding the Option key down during restart. Nothing worked. I even tried command-option-P-R to reset the PRAM, in case it was a weird power-related issue. I never got the multiple chimes. Just the initial chime and the grey screen, with no disk activity.

I then proceeded to take the machine home, plugged it in, and it started properly right away. Even without having it connected to a display, I could hear the hard drive churning. This suggested to me that it might be a problem with the power supply at the store. So I went back to the store with a different power bar and a different power cable. I tried starting the computer at the store before connecting it to the display, and again it started properly right away, with the hard drive churning. I plugged the display in after the Mac Pro had already started, and everything was in order. Then I tried to restart and I got the grey screen again.

Finally, I put 2 and 2 together and figured that it might be a problem with my good old 23” Apple Cinema Display. And sure enough, after a few more restarts for testing purposes, I was able to narrow it down to the USB connection from the display to the Mac Pro. If I just plugged in the DVI cable (from the ADC-to-DVI adapter) and nothing else, everything worked fine. If I also plugged the USB cable coming from the ADC-to-DVI adapter into one of the Mac Pro’s USB ports, then upon restarting the machine I would get the grey screen.

It also finally dawned on me that this same USB connection might have been the cause of the problems (with the Mac Pro not waking up from sleep properly) that my wife had been having for the past year. The grey screen problem was new, but might be part of the same cluster of USB-related issues.

Since the USB connection still worked properly (for a mouse and keyboard anyway) if the USB cable from the display was connected to the Mac Pro after restart, I just told her that, whenever she needed to restart the machine, she should unplug the USB connection temporarily, and then plug it back in. I also changed the power-saving settings so that only the display would go to sleep, leaving the Mac Pro itself running (but with the hard drives going to sleep when unused).

Eventually, it will make more sense to get a USB extension cord and plug the keyboard and mouse directly into the Mac Pro and forget about the display’s USB connection altogether. It still works fine as a display, and with such a fine-quality screen still working very well after 11 years, I think I can say that I got my money’s worth.

But it was definitely a weird issue that a USB connection would cause the Mac Pro to fail to start up properly altogether, even though that same USB connection still works properly (apparently anyway) if it’s only connected once the Mac Pro is already up and running. It was, as usual, quite satisfying to be able to fairly quickly pinpoint the problem with this level of accuracy and find a reliable workaround that does not require the purchase of any new equipment (for now). And, as my wife said, what would she have done if I hadn’t been around and I hadn’t been able to bring my general level of expertise and my fairly intimate knowledge of this particular 23” Apple Cinema Display? (I didn’t tell her that, if I wasn’t around, she probably wouldn’t be using such a computer with such a display in the first place.)

All that being said, there’s definitely something weird about a USB connection being able to interfere with the ability of a machine to start up. It reminds me of that problem I had a few years ago with a MacBook failing to start up because of a defective hard drive. Even though the MacBook’s CD/DVD drive was still working fine, it was impossible to get the MacBook to start from a system DVD until I physically disconnected the internal hard drive from the motherboard — just like it was impossible, here, to get the Mac Pro to start until I physically disconnected the USB connection from the display.

Is there something about Intel processors that explains those weird startup issues? That MacBook should have been able to boot from a system DVD even when its internal hard drive was failing. And similarly, that Mac Pro should have been able to boot from its internal hard drive even when it was connected via USB to a display with defective USB ports.

Of course, I suppose it’s also possible that the real problem is with the DVI-to-ADC adapter and not with the display itself. But since I cannot use the latter without the former, I guess I’ll never know. That proprietary ADC thing was a major (yet typical) mistake on Apple’s part. It is good that I am still able to use a display with such a proprietary and obsolete connection after all these years, but the problem might never have happened if Apple had fully embraced DVI from the get-go.

This entry was posted by Pierre Igot on Saturday, November 30th, 2013 at 3:48 pm and is filed under Macintosh. You can follow any responses to this entry through the RSS 2.0 feed. Responses are currently closed, but you can trackback from your own site.