G5 Quad and dual 30?/23? monitor setup: It was a defective video card

Posted by Pierre Igot in: Macintosh
January 29th, 2006 • 3:04 pm

A couple of weeks ago, I wrote about weird visual artefacts I was seeing in certain situations in a certain area of the screen on my secondary monitor, an older 23″ ADC Apple Cinema Display connected to the second DVI port on my G5’s stock NVIDIA GeForce 6600 video card, with the power supplied to the ADC monitor by an Apple ADC-to-DVI adapter.

I am happy to report that the problem has now been solved. I first called Apple about the problem in early January, and they told me that I would have to take my equipment to an Apple Authorized Repair shop. Apple gave me a case number to give to the repair shop so that they could look up in the case information in the database.

For me in southwest Nova Scotia, the closest authorized repair shops are in the provincial capital Halifax, and this means a 600-km round trip. I first phoned the repair shop and explained the situation. I also explained that I suspected a defective video card, and was perfectly comfortable with replacing it myself, if that could be arranged. I really didn’t fancy having to bring all my equipment, including the G5 Quad, the 30″ display, and the 23″ display to Halifax.

The repair shop guy told me that he could not look up the case information. I told him that Apple had told me that he should be able to. So he said he would try and investigate the matter and get back to me.

I waited for a couple of days and decided to call Apple again, at the very least to tell them that there appeared to be some communication issues between them and their authorized repair shops. I also explained again that I would really appreciate it if we could come up with a solution that did not involve having to move all this equipment.

Much to my surprise, later on that same day (around 10 pm my time, actually), I got another call, from an Apple engineer this time. He was very friendly and offered to take me through a few steps to better circumscribe the problem. The first step involved unplugging the 30″ display altogether. The problem was still there on the 23″ display, so that helped us determine that the problem was not due to the combined load of the 30″ display and the 23″ display on the same card—a combination that is, after all, officially supported by Apple for this particular machine. Even though it is the maximum for the GeForce 6600 (if you want to use two 30″ displays, you have to get a more powerful GeForce card as an option), it is a configuration that this particular video card is expected to be able to handle.

The next step was to plug the 23″ display on the other DVI port, i.e. the more powerful one normally used to drive the 30″ display. The problem was gone. This helped us confirm that the problem was not with the display itself (which I knew, since I had been using this display with my G4 with no problems) or with the ADC-to-DVI adapter, but likely with the video card itself, and more specifically with the second DVI port on that card.

At that point, the engineer’s only solution was to invite me to go to the “local” authorized repair shop. So I got back in touch with them, and this time they knew more about the case (so obviously they must have been given access to it), and decided to set up an appointment. The tests with the engineer had helped us determine that I didn’t have to bring the 30″ display along, which was a big relief. But I still had to bring both the G5 and the 23″ display, in part because it was an older ADC display and they didn’t have that particular kind of display handy, and we needed to be sure we’d be able to reproduce the problem reliably.

In order to minimize travel requirements, the repair shop person also offered to pre-order a replacement video card from Apple, so that they would have one in stock when I got there and would be able to swap the video card and see if it made any difference right away. (I didn’t fancy having to travel all the way there just to show them the problem, and then have to go back again once they got the replacement card.) It turns out that they can order replacement parts from Apple and then ship them back to Apple within a given time frame in case the part in question is not the problem.

The part took longer to arrive than initially expected, but it all worked out in the end, and they had the card in stock last Wednesday, so I went there on Friday.

Because of my fairly bad experiences in the past with the other authorized Apple reseller/repair shop in Halifax, I had tried hard to locate another repair shop in the province, and it turned out that there was one other authorized repair shop on the campus of the province’s largest university, Dalhousie University, in downtown Halifax. (I had heard about them, but had never really investigated the issue, because I thought the shop might be exclusively for university students.) The reseller/repair shop is called PCPC and, based on my experience with this particular problem, they are a much better alternative for Mac users in the province. They obviously cater to the fairly large local student population, but they are open to anyone in the province who needs help with Apple hardware. They also have fairly reasonable hourly rates for out-of-warranty problems.

I got there on Friday afternoon at 1:30 pm, brought my equipment in, and sat down in the waiting room while my equipment went in the back for tests. After about 10 minutes, they called me in, telling me that they couldn’t reproduce the problem. I was only half surprised, because I doubted that all the required pieces of information had been communicated to the right person. So I went in, and saw that they had plugged the display into the wrong DVI port, i.e. the one that worked fine. We plugged the display into the “right” DVI port, and sure enough, the problem was there and I was able to show it to them. They were quite surprised and confirmed that they had never really seen anything like it before. (If a video card is bad, you expect no signal at all, not a good signal with just a few artefacts, changing depending on the contents of the screen.)

They got the replacement video card out, made sure it was the right model, and made the swap. They started the G5. I opened a few windows and tried to replicate the problem—and it was gone! No matter how hard I tried, I could no longer make the visual artefacts appear in this area of the screen with Safari windows, as I usually could with the other card.

We decided that the problem was solved, and less than an hour after my arrival, I was back in my car with my G5 and my display all in perfect working order. There was no paper work, no exchange of money (I am still under warranty, of course), and the overall service was excellent. Everyone was friendly and helpful, and nobody ever questioned, at any point, my ability to determine that there was indeed a problem—even though it was a fairly unusual one.

We still don’t know exactly what was wrong, but it was obviously something on that particular video card. Maybe defective video RAM? Who knows? The problem is out of my hands now. It is up to the local repair shop and Apple to decide whether this matter is worth investigating any further. It could be a one-off problem, or it could be a problem with a batch of cards that has not generated more reports because it only occurs when the video card is used with a particular combination of displays. Obviously people using their G5 with another kind of display setup won’t see the problem and might never know that they have a defective video card.

One thing is for sure, however. While I would have preferred not having any such problems in the first place, my experience with Apple and with the local repair shop was excellent, and I will most definitely recommend this shop to my local Mac tech support customers for hardware problems that I cannot solve myself from now on. And if it’s the worst problem I ever have with this G5 Quad, then I won’t be complaining.

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