How a Bad DisplayPort Cable Can Ruin Your Day

[Bifurk8]

I like to think I'm pretty knowledgeable when it comes to troubleshooting anything PC-related. I'm sure many, if not most, WSGF members feel the same way. We're PC enthusiasts, after all.

Well, I just wanted to publicly admit that I'm an idiot. For about 2 months I've been struggling with a BSoD error related to atikmpag.sys on my Windows 7, core i7, 2x 5870 Crossfire system. It's been up and running pretty much perfectly for a couple of years. Sure, I've run in to software issues, driver problems, overheating, Eyefinity compatibility, etc. But, that's all been easily resolved once identified. This particular issue was insidious, however. I tried everything!

First, I assumed it was a driver issue. At the time I think the 12.1 Catalyst drivers had just been released. So, I rolled back to 11.10 or so. After a day or two, I had another blue screen. At this point, I'm thinking I've got a heat-related issue, since the problem is intermittent. I keep a pretty clean system, but I removed the CPU fan and graphics cards and cleaned the fans thoroughly. Then, I start to monitor temps and don't notice anything above normal; BSoDs continue anywhere from every couple of days to as often as every couple hours. I tried a different Crossfire bridge without any luck. I figure I've got bad card. So, I pull one of the cards from my system but still keep crashing with a bluescreen related to atikmpag.sys. I tried swapping the cards out. I tried each card in different PCI-E slots alone and together. Finally, I threw in the towel. I'm not savvy enough to attach a debugger to the AMD drivers to figure out exactly what's erroring out so for the first time in over 10 years, I formatted my system partition and reinstalled Windows to try to fix an issue. I'm not proud of resorting to it, as it's pretty much admitting defeat, but I was desperate.

Guess what? BSoDs continue!

Finally, after all of this, I decide on replacing the DisplayPort cable as the last possible point of failure. I should have mentioned that I'm running 1 native DisplayPort and 2 DVI ports. I replaced it with one from Accell off Newegg and it's been over a month without any further BSoDs. I've heard of plenty of issues out there with DisplayPort adapters, but never thought I'd have an issue with a straight DisplayPort cable distributed with a Dell monitor. Back in the BNC and D-sub 15 days, the worst thing a display cable would do is take your monitor outside its recommended specs and cause no signal or a distorted signal. Having a Windows BSoD from a bad display cable was definitely an eye-opener for me.

Expect the unexpected!

*Edit: I'm not running 1 native DisplayPort and 2 HDMI ports. I'm running 1 native DisplayPort and 2 DVI ports. Duh!

[Haldi]

Wtf! Some1 with tecnical background can explain that?

[Gilly]

I think DP is classed more or less as a hot-plug device, similar to USB.

I guess that when you have your 3 screens, the DP must be a proper connection all the time, and then the signal to the 2 DVI screens just gets sent. So I guess that if the signal got lost (or whatever) on its way to the screen, or on its way back, that it could of caused the card to effectivly think the screen was gone, thus breaking the eyefinity group.

Why it wouldn't just jump back to 1 screen and complain about a DP error, I don't know.

I think the secret lies in the fact that you NEED a DP connection on a 5870 to get eyefinity to work, and therefore a break in the chain somewhere caused it to crap out.

Glad you got it fixed though!

[Bifurk8]

Thanks! It's been quite a relief having a stable system back! Oddly enough, this problem occurred when running in both Eyefinity and extended-desktop modes in both 2D and 3D applications. Prior to the bluescreens, I did have occasional problems with the DisplayPort monitor blacking out and coming back up with a Windows dialog saying that the Display Adapter had stopped responding. But, it was never very common and I didn't think much of it at the time. Now, I definitely think I'd gotten a shoddy cable from the start and it just took a couple years to catastrophically fail.

My best guess is that the DisplayPort specifications haven't been very well enforced and manufacturers are making cards/cables/drivers that can't properly handle unexpected failures. That's one reason I went with the Accell cable as a replacement. They've been on the DisplayPort bandwagon for a while and I felt more comfortable ordering from them than a manufacturer without any ties to the DisplayPort spec. So far, it's proven to be a good move. But, who knows? I really just wanted to get my experience out there in case anyone else runs in to the same thing. I certainly didn't find any similar cases while I was struggling with it.

[Zencyde]

Oh my God. I"ve been having this same exact issue and I just narrowed it down to the Displayport cable as well. Already sent in another order of 3 just in time for my 5x1P setup. Glad to see you've figured it out! Was Hell for me, too. I couldn't upgrade past 12.2 and it BSoDed my system so hard that it wouldn't even boot into safe mode with the latest 12.6 drivers. Ugh, piece of crap cables.

[rdqlus]

Hmm, intredasting ....

I debug silicon that implements the DP spec for a living. I'm curious what could be happening here. The only cable problems we've seen at work were some monoprice ones when DP 1.1 first came out. They were wiring the power lines straight through to the monitor which shouldn't be. Those power wires are only for powering an adapter.

In this case, I'm guessing the ATI driver is crapping out when something goes wrong on the Aux pair or that the hot-plug detect wire is faulty.

[Haldi]

so sending you that defective cable might help ? Maybe we can convince Zencyde or Bifurk do to that for future references...

[Bifurk8]

Hi rdqulus,

I don't have any need for my original displayport cable that seemed to be the cause of my issues. Of course, I'm betting that you're right about the cable itself not being the only culprit. I'd say it's likely a combination of something out of spec with the cable, the graphics card design, drivers, and/or monitor. But, if you'd like to fiddle with the cable and live in the US, I'd be happy to get it to you. PM me if you're interested in checking it out.

[Zencyde]

Ah, late here. But I'll also ship of my cable if you'd like. No use for it now.

[Downtown1]

I'm with rdqlus on there, I haven't done DP but I have done drivers for other differential buses on embedded systems... the BSODs were caused by buggy drivers that don't handle faulty physical connections. To be fair though this is the first time I can think of that I've heard of cables on a desktop PC causing BSODs. Usually stuff just silently fails.

[Zencyde]

Yeah. It threw me off completely to find that the cable was causing the issue. Especially after it worked fine for so long. It reminds me of that time that I was having trouble getting Windows XP on a friend's machine, and it turned out that the DVD drive had an issue. It would install sometimes just fine, but BSoD on first reboot. Sometimes it would BSoD during the installation. Windows 2000 would install and boot just fine. So, I figured the DVD drive didn't have any issues, as I could get other operating systems to install, including Ubuntu. It took the better half of a year before finally figuring out it was the drive that had an issue. Gutted one from another system to do the install and it was fine after that. Ugh.. Windows...

[Defcoms]

Long one lurker first time poster...

With that out of the way.

Bad DP cables have been giving me issues for months now. I figured out the why though.

If you read the VESA Displayport standard it states.
Here on page 147

3.2.2 DP_PWR Wire

A standard DisplayPort cable must have no wire for the DP_PWR pin.
Only captive cables supplied with cable powered Branch Devices or cables permanently attached to Sink
Devices are permitted to have the wire for DP_PWR. These captive/attached cables must have a standard
DisplayPort plug connector (as specified in Section 4.2.1) on one end only. The other end must either be
permanently attached or have a custom connector.

If you look at the pin out for a DP cable.

Pin out

External connector (source-side) on PCB
Pin 1 ML_Lane 0 (p) Lane 0 (positive)
Pin 2 GND Ground
Pin 3 ML_Lane 0 (n) Lane 0 (negative)
Pin 4 ML_Lane 1 (p) Lane 1 (positive)
Pin 5 GND Ground
Pin 6 ML_Lane 1 (n) Lane 1 (negative)
Pin 7 ML_Lane 2 (p) Lane 2 (positive)
Pin 8 GND Ground
Pin 9 ML_Lane 2 (n) Lane 2 (negative)
Pin 10 ML_Lane 3 (p) Lane 3 (positive)
Pin 11 GND Ground
Pin 12 ML_Lane 3 (n) Lane 3 (negative)
Pin 13 CONFIG1 connected to Ground1)
Pin 14 CONFIG2 connected to Ground1)
Pin 15 AUX CH (p) Auxiliary Channel (positive)
Pin 16 GND Ground
Pin 17 AUX CH (n) Auxiliary Channel (negative)
Pin 18 Hot Plug Hot Plug Detect
Pin 19 Return Return for Power
Pin 20 DP_PWR Power for connector (3.3 V 500 mA)

On a standard Displayport cable being used to hook up monitor to video card.
Pin 20 DP_PWR Power should not be connected. It is back feeding 3.3v back into the video card causing all kinds of issues. A lot of company are pushing out products that are not following the correct VESA Displayport Standards.

I tested this by removing my video card and connecting Displayport cables. These are Monster Digital Life cable.




Measured here from negative lead on meter to screw on back of card.



And Reading 3.3v on video card. (MSI 7970 reference card)



Just some info a thought I would share. I am still lookig for some good cables. I am open to suggestions.

[Haldi]

On a standard Displayport cable being used to hook up monitor to video card.
Pin 20 DP_PWR Power should not be connected. It is back feeding 3.3v back into the video card causing all kinds of issues. A lot of company are pushing out products that are not following the correct VESA Displayport Standards.

Ehm, the Monitors gives 3.3V BACK into the GPU?

Isn't the GPU supposed to give 3.3V Out to any adapter you might plug in ?

Verry interesting find! Thx a lot! Gotta test that with my two miniDP->DP cables!

P.S Any means to contact AMD and ask if they have any idea what this 3.3V input might cause?

[Defcoms]

I am unsure what kind of effect the 3.3v has had on the card/cards. I am getting system freezes though while playing sniper elite v2 still even after getting some compliant cables. Using the non compliant cable I was getting image frozen and buzzing/sound were only cycling power will reset my system on a lot more games. I am unsure if this is a driver issue with running eyefinity and trifire 7970 or if the cards are damaged. I am going to wait for the next official driver from AMD to see if this issue is fixed if not then I am going to RMA the cards one by one.

The cables I found to be compliant are Belkin Displayport Male to Displayport Male. I did away with using the Mini-DP to DP cables and am using the Mini-DP to DP female dongle that was included with my MSI reference 7970's.

Here is a link to the compliant cables. Hope they help someone out.
http://www.amazon.com/gp/aw/cr/B0017U61M8/ref=aw_d_cr_electronics

The cables I found to be non compliant were startech.com Mini-DP to DP I got from amazon.
Monster Digital Life Mini-DP to DP cable.
I tested 2 cables from both manufactures.
I am running one DVI and 2 displayport connections for 3x1 eyefinity.
Using 2x ASUS VE278Q, 1x ASUS VK278Q monitors.

As for you question isn't the card suppose to supply 3.3v. I don't think that is the case if you read the spec only place 3.3v is pin 20 and that is not suppose to be used connecting monitor to video card. It is only suppose to be used for powered branch devices or cables permanently attached to sink
devices.

[Haldi]

Well yeah -.- a lot of people using Crossfire get unwanted Freezes ingame when playing for a long time (me included)




So if the Card does not output any voltage via miniDP, how do these "Active miniDP->DVI" adapter work which have no USB powered? does the DVI cable from the Monitor comes with energy?

[Defcoms]

I have not used any adapters but if you are talking about the ones AMD announced that are active and don't need USB power here is some info..

eyefinity requires an "active" cable, because the conversion from DP to DVI or HDMI requires additional power if you want to use larger resolutions. Most active cables had a separate usb plug that needed to be plugged into your pc for the cable to work. The new AMD adapters have a new decoder chip that doesn't require as much power, so no additional usb plug is necessary:

"Internally the new cable uses a single piece of silicon with a DispalyPort decode and a TMDS for the DVI output. This greatly reduces the power requirement (hence the reason no additional power is needed) and should also eliminate the flicker issue that is prominent with the powered Dual-Link adapters."

So I am reading this as the adapter gets enough power from the DP signal that it does not require additional power.

[Haldi]

List of official supported DP cabels.
http://www.displayport.org/products-dat ... ufacturer=

Recently VESA has experienced quite a few complaints regarding troublesome DisplayPort operation that ended up being caused by improperly made DisplayPort cables. These “bad” DisplayPort cables are generally limited to non-DisplayPort certified cables, or off-brand cables. To further investigate this trend in the DisplayPort cable market, VESA purchased a number of non-certified, off-brand cables and found that an alarmingly high number of these were configured improperly and would likely not support all system configurations. None of these cables would have passed the DisplayPort certification test, moreover some of these cables could potentially damage a PC, laptop, or monitor. We have not seen problems with the cables supplied by major computer brands, or major computer accessory brands, nor have we seen any problems with any of the cables that have been DisplayPort certified.

We expect to be adding more certified cables to our published list in the future and will continue to encourage DisplayPort product certification. To achieve the best of DisplayPort’s capabilities, we highly recommend using DisplayPort certified cables, or those from major brand names. Please continue to send us any questions or reports of bad cables that you may be experiencing.

– Craig Wiley, Chairman, VESA

http://www.displayport.org/cables/how-t ... a-bad-one/

so they do know about that problem!

[Jumpman]

Sorry for bumping old thread, but this may be a problem I'm having too. I get these lines/static when using DP on my GPU, but when I use HDMI, the lines disappear. I have used the same DP port and cable before, but after a BSOD these lines started happening. Is it because of a bad DP cable? I was just using the DP cable that came with my monitor.

[dfwallace48]

New member and first post here

I'm thinking a bad DisplayPort cable could be my issue...

Since Nov of 2013, I've had 3 Galaxy nVidia 780 cards fail ( don't have a great track record based on many forum posts), or so I thought. The last one failed last weekend, and that's when I started to think that it was my power supply. (Corsair HX850). I finally brought my comp to a local tech guy. Just called, and they said they ran a full diagnostic and the computer is working fine... What the f***.

I do remember that the DisplayPort cable is quite hard to insert and remove from the port on the video card....

What do you folks think?

My system...
*Asus P8P67 Deluxe MB w/ latest bios
*Intel i7-2600k (never OC'd)
*Galaxy nVidia 780 (never OC'd)
*8 GB Corsair Vengeance
*Xonar Essence ST sound card (internal)
*Intel x25 SSD
*Corsair HX850 PS
Eizo FG2421 monitor
*Win 7 pro 64bit OS