Using large monitors with a dual-link DVI-D Power Mac video card

[gsteemso]

I have two Power Mac G5s, one of which is a Late 2005 dual-core model and as such has a video card that will do 2560x1440. I also recently acquired a new monitor with a native resolution of 2560x1440. Unfortunately, the new monitor has HDMI (well, and DisplayPort) inputs, as new monitors often do, while the primary display outputs on each of my G5s are dual-link DVI.

It turns out that the cheap little DVI-HDMI adapters you can get usually only convert single-link DVI, or if they do dual-link, there's some sort of technical issue that stops them from getting past 1920x1200. What that issue is, I have no idea. (I think it might be related to the signalling speed – DVI has a fixed signalling speed that cannot convey more than X amount of data per second per link, while newer HDMI standards allow faster signalling, which I suspect would be the modern go-to solution for what are now considered mid-range resolutions like the 2560x1440 I'm attempting, because it would be simpler than wrangling dual data channels.)

In any case, I bought an adapter on Amazon that claimed it could adapt dual-link DVI at resolutions up to 2560x1440, but it didn't succeed in doing so for my setup. In the faint hope it was merely defective, I have returned it for exchange, but I am not optimistic. A friend tells me that the very early dual-link DVI stuff tended to not interoperate well (or at all) between vendors, so there pretty much has to be some nuances to the technology that not everyone implemented quite the same way. I hope someone out there knows enough about what Apple and its vendors did in this regard to tell me how to get around the problem.

The whole reason I got a new monitor was because old monitors produce far too much heat, so doing something like acquiring a 30" Cinema Display would not really solve my problem even though it should technically work; and even if I had the budget to try a different new monitor after buying the first one, I'd be genuinely shocked if anyone made a modern monitor with Power Mac compatibility specifically in mind. Working with what I have is probably my only option, so I basically _need_ to identify some sort of active-adapter solution.

So, yeah, that's pretty much it. Has anyone else out there had any luck driving a non-Apple monitor past 1920x1200 from a Power Mac G5?

 

[joevt]

What adapter did you get? It was probably not Dual Link.
What Dual Link DVI supporting GPU are you using?

I use this one with my Quad G5's Nvidia GeForce 7800 GT:
https://gefen.com/product/dual-link-dvi-to-mini-dp-converter/
It can do 4K30, 1440p60, and 2560x1600 60Hz. etc. I suppose anything up to 330 MHz pixel clock.

HDMI is always Single Link (the Dual Link HDMI connector was never used by anything?).

HDMI 1.0 and Single Link DVI is max 165 MHz.

HDMI 1.4 is 340 MHz.

HDMI 2.0 is 600 MHz.

HDMI 2.1 adds Fixed Rate Link modes that are not the normal 3 lane TMDS modes used by earlier HDMI and DVI.

 

[gsteemso]

It was this one on Amazon, which I agree does not look like anything very capable but was explicitly advertised as being dual-link up to 2560x1440: https://a.co/d/7wCyHFZ

The graphics card is a GeForce 6600 16-lane PCIe card. It has one DVI port that can do up to 2560x1440 and a second that can do up to 1920x1200 (I believe, not 100% sure if the second port does 1200 or merely 1080 vertically). System Profiler lists it as having 256 MiB of VRAM.

I will look into that Gefen adapter – just knowing that someone actually got something to work for this purpose is worth a lot. Thanks!

 

[joevt]

It was this one on Amazon, which I agree does not look like anything very capable but was explicitly advertised as being dual-link up to 2560x1440: https://a.co/d/7wCyHFZ

Well, the connector is Dual Link. But probably none of the Dual Link pins are connected to anything. Also, there doesn't look like there's enough room or power for the chips required to convert Dual Link to Single Link.

I don't think I've ever seen a Dual Link to Single Link adapter that doesn't just disconnect the Dual Link pins. You have to do Dual Link to DisplayPort (using Gefen or similar adapter). then DisplayPort to HDMI. Chaining adapters like that doesn't always work. So it's best to have a display that accepts DisplayPort.

 

[gsteemso]

Good gravy, they want $300 for that thing! There HAS to be something out there that costs less than the whole blasted computer did. Oh well, you've still given me more keywords to search on. I do note that the adapter I bought claimed to do what it claimed to do using HDMI 1.3 rather than 1.4, so that might be the problem – it may be physically impossible for both claims to be true, in which case I will have to report them for false advertising. Investigations continue.

 

[gsteemso]

I note that the Gefen product is explicitly stated to only support Apple's Mini DisplayPort monitors. Did you get it to work with third-party gear?

 

[joevt]

I do note that the adapter I bought claimed to do what it claimed to do using HDMI 1.3 rather than 1.4

Not a significant difference.

Good gravy, they want $300 for that thing! There HAS to be something out there that costs less than the whole blasted computer did.

That's how you know it's not a passive HDMI to DVI adapter like the one you bought.
Atlona AT-DP400 is an alternative. Don't know if it's for sale anywhere. ebay?

I note that the Gefen product is explicitly stated to only support Apple's Mini DisplayPort monitors. Did you get it to work with third-party gear?

It's DisplayPort. Shouldn't matter. I don't have Apple DisplayPort displays. It works with all my DisplayPort displays.

 

[quicksilver]

I've been picking up Atlona AT-DP400s (for the 27" Cinema Display) and AT-DP200s (for the 24" Cinema Display) as they turn up cheap on eBay. Cinema Displays are frequently on Facebook Marketplace around me, marked as anything from Apple monitors to Thunderbolt Displays to broken iMacs. I paid under $30 for the last AT-DP400 I bought.

They're no 4K-5K display, but I don't think you can find a better built 2560x1440 monitor potentially priced under $150 with the DL-DVI to mini displayport adapter.

I haven't experimented with the Atlona adapters and any non-Macs yet, but I have a HP Elitebook laptop plugged into a USB-C docking station with two Displayport connections. Two 27" Cinema Displays are connected via these adapters from Amazon.

Some of Extron's older products seem like they could work well for connecting newer monitors to old DVI or even VGA and other analog outputs. There website has lots of details on legacy products. They can still be very expensive on eBay. One trick to get something cheap is to find an item you want with no power supply at a good price. Then find another item that's not popular and is selling cheap but includes the power supply. Almost all of their products use the same one.

 

[gsteemso]

I've been picking up Atlona AT-DP400s (for the 27" Cinema Display) and AT-DP200s (for the 24" Cinema Display) as they turn up cheap on eBay. Cinema Displays are frequently on Facebook Marketplace around me, marked as anything from Apple monitors to Thunderbolt Displays to broken iMacs. I paid under $30 for the last AT-DP400 I bought.

I found an AT-DP400 for that price! I also found one that from the photos was actually a mislabelled AT-DP200 (the difference being that those are single-link only), so buyer beware.

They're no 4K-5K display, but I don't think you can find a better built 2560x1440 monitor potentially priced under $150 with the DL-DVI to mini displayport adapter.

Probably true, but as I understand it they are not LED backlit and thus produce too much heat for my use case. Very good option for those who don't have that issue though.

I haven't experimented with the Atlona adapters and any non-Macs yet, but I have a HP Elitebook laptop plugged into a USB-C docking station with two Displayport connections. Two 27" Cinema Displays are connected via these adapters from Amazon.

DisplayPort in general sounds like it is better managed by the industry in terms of not having as many interoperability issues.

Some of Extron's older products […] One trick to get something cheap is to find an item you want with no power supply at a good price. Then find another item that's not popular and is selling cheap but includes the power supply. Almost all of their products use the same one.

A good trick indeed! I’ll bear that in mind.

 

[gsteemso]

I did indeed acquire an Atlona AT-DP400 for a good price. Alas, I got a black screen when I tried it, with each of two monitors. The seller was very good about it and refunded my money before I even asked, but I've had to order a second one. This one's supposedly new in box, so I shall see what happens when it arrives.

The monitors were both from the same manufacturer, so I hold out the faint hope that it's a timing issue or something and the first unit might actually work if I had a better monitor, but the chances probably aren't great. Has anyone got any knowledge of how well DisplayPort monitors generally handle a variety of refresh rates? Maybe the monitor is cheap enough that it only understands a small set of rates? I don't know what I don't know _about_.

 

[joevt]

Did you have a second display connected so that you can see the Displays preferences panel for the display that was black?
Or use screen sharing?
Then see what display options are available?
Or use SwitchResX to view more options?

Connect the monitor via HDMI adapter to modern Mac and extract the EDID.
Connect the Atlona with the monitor to a modern Mac using HDMI (or Dual Link DVI have you have a GPU) and extract the EDID.
Use edid-decode to decode the EDIDs and then compare them.

My AllRez app can be used on any Mac OS X version to extract display info. Though you might need to recompile it. Use the 10.6 project for 10.6 and earlier versions of macOS.
https://github.com/joevt/AllRez
Run it for each display connection, zip the results and we can compare.

 

[gsteemso]

Well. I hadn’t even thought of trying about three quarters of those, so thank you for that nudge out of my mental box, so to speak. :¬) The actual state of affairs is even stranger than I thought… it turns out that the first Atlona adapter does in fact work correctly, so honesty has compelled me to contact the seller to ask how to reverse the refund they sent me. The cause of my difficulties turns out to have been some weirdness going on between the video card and the monitor, whereby the former absolutely refuses to emit maximum-resolution video unless its secondary port is connected to a monitor; not only that, the secondary display connection _must_ be established first. This holds true even on reboots, which – since I only have (room for) one monitor – means I must switch inputs to the secondary display feed until booting has resolved into a clear picture of the desktop, and only then may I switch back to the primary feed… which does indeed work perfectly at the full 2560x1440 resolution of the monitor. (The video card can do an entire 2560 x 1600, but I have yet to locate ANY reasonably current monitor of that native resolution, let alone one with the correct physical dimensions that is within my budget.)

The monitor is itself somewhat worthy of note, if for unfortunate reasons – an Asrock "Phantom Gaming" PG27QFT1B, it is the flakiest PoS I have had the misfortune to buy in years (beaten out only by a KVM switch I bought last month that destroyed one of the video cards it was connected to). The on-screen controls absolutely refuse to appear unless the picture is stable and, preferably, active, which is a real problem when the menu you want is the one for switching to a stable input source. (I had to disable the feature that automatically switches to a newly active video input, because it was ping-ponging "I'm active!" / "I'm asleep!" status back and forth to one of my computers, such that neither would stabilize long enough to break the loop.) Further, it seems to have an intermittent "I'm here" presence-detect signal, as it will frequently go black for a few seconds with no obvious cause (I'm pretty sure it’s the video card stopping sending the picture rather than the monitor failing to display it, but it’s still something I never had to worry about with my old monitor).

Interestingly, said monitor does indeed also appear to have a hilariously restricted set of resolutions and refresh rates it can accept. It’s pretty permissive at lower resolutions, but at the high end there are only a handful of settings it will respond to. Lesson learned, maybe? Next monitor, I guess I will have to do some really exhaustive research on this stuff. Some of it doesn’t seem to be widely advertised, to put it mildly.

I can at least be fairly confident of its flexibility at low resolutions. I recently acquired a surprisingly affordable VGA-to-HDMI converter in order to put a Quadra 840av display onto the same monitor as all the others, and it works like a champ! 10/10, five stars, would recommend. The manufacturer is some obscure outfit I'd never heard of called Foinnex, and the model is just called "VGA to HDMI Adapter" rather than a definite part number or similar code – the "adapter" part is all that distinguishes it from their other products – but they do good work.

So, this turned into a lengthy hardware review, with mixed results. But I _got_ a result! It’s a very inconvenient result that doesn’t always work, but I can use the thing! w00t, etc. Hopefully some part of this waffling will be useful to those who come after.

 

[gsteemso]

Further discoveries relating to the weird, intermittent black screen: It only happens if there is more than a certain average percentage of bright pixels on screen. I've got Terminal.app set to green-on-black, so it almost never happens with that in front (the exception being if the "visible bell" feature momentarily flashes the whole screen white at the wrong moment). Conversely, my text editor or a web page that's got a white background will blink off every few seconds like clockwork. I think this is an even weirder problem than the video card that only works properly if both ports are active! At least I can be about 60-70% sure it's the aforementioned PoS monitor at fault... futzing around with its internal brightness settings seems to work.

tld,dr: Don't buy the model of monitor I've got.

 

[gsteemso]

I have now tried Mini-DisplayPort-to-HDMI adapters from two different manufacturers, to a complete lack of success. Conversation with tech support from the first company implies their product, which apparently uses off-the-shelf conversion chips, likely puts out a different refresh frequency than the monitor can understand – as I mentioned, it seems disgracefully limited in what formats it will accept at full resolution. Le sigh. I guess I’m just going to be stuck switching the monitor’s input source by hand every time I switch to or from that KVM position.

 

[gsteemso]

I have acquired a (nominally) much better monitor, and also had a few tries with SwitchResX. Alas, my efforts ended in failure, but I now know that (a) the monitor is not more than a small part of the problem, and (b) no matter what I do in SwitchResX, the picture never makes it through a miniDP-to-HDMI conversion.

I have also learned that the intermittently blank display problem is caused by the video card briefly overheating when given too bright of a picture to display. Something similar but less extreme happens to the other G5 when both its monitors are trying to show actively changing imagery over large areas.

Long story short, I’m still stumped, but maybe this exerience will illuminate similar issues somebody else is having. You never know.

 

[joevt]

the picture never makes it through a miniDP-to-HDMI conversion.

Remind me, what Mac, OS, GPU, miniDP-to-HDMI adapter, cables, and display are you using?

Power Macs don't have DisplayPort so a miniDP to HDMI conversion isn't useful.

 

[gsteemso]

It’s an Atlona DP-400 dual-link-DVI to mini DisplayPort converter, hanging off of a Dual Core PMG5. I learned about an hour after making that last post that the reason I’ve not been having success with the mDP-to-HDMI conversions is probably that the adapters I’ve been using are not active. Despite looking almost identical on the outside, apparently passive adapters only work with DisplayPort++, which I’m going to go out on a limb and hypothesize that the Atlona does not have... y’know, what with it being older than that standard and all. I’ve got an active adapter, which I verified supports my resolution and refresh rate (by asking the flaky AI bot on their website, so 100% not going to be wrong *wince*), on order for arrival in a few days. AND THEN WE’LL SEE WHO’S TOO STUBBORN TO SHOW A PICTURE, oh yes we will... *mutter*grumble*

...I may have gotten just a tad wound up about this.

 

[CC_333]

...I may have gotten just a tad wound up about this.

You're not the first, and you won't be the last....

c