I've had a thread going here on TH about this topic the last several days, and I I'd like to share the broad conclusions with the rest of the community. Long story short, as the thread title says, I think I stumbled onto a design problem with Asus's P8 boards, specifically the P8Z77-V Pro and the P8Z77-V/Thunderbolt Pro.
Take a look at the cluster of components behind the secondary PCIE 2.0/3.0 slot. If any piece of conductive material (like a GPU I/O bracket, for example) touches those components, you will short out your on-board audio chip and potentially more than that. It doesn't matter if the system is shut down, nor does it matter how long the conductive material was in contact with the components. If anything conductive so much as grazes those parts you can kiss your on-board audio goodbye for good.
I stumbled upon this when I was trying to install a second GPU into that slot. I had the system powered down completely at the time. Getting the secondary GPU into the slot was somewhat of a chore due to the ever-decreasing amount of motherboard real estate as my build was coming together. This lead to more than one instance where the insertion didn't go flawlessly. As I was trying to slide the I/O bracket in place, I managed to brush the components mounted to the PCB just millimeters away from the second PCIE slot. This immediately sent a disturbing "POP" through the speakers. Not good.
After the GPU installation, I booted into Windows, did a series of GPU benchmarks with both cards, and was ready to call it a night when I noticed my computer no longer played audio. Not only was it no longer playing audio, it didn't even seem to register that it ever had the capability to play audio. The Windows Sound/Playback dialog showed the "Speakers" option as completely grayed out, and the system would not correctly recognize that anything was being plugged into/out-of the audio ports. I re-flashed the BIOS and reinstalled the drivers but nothing helped. At this point I had no idea what was wrong, so I RMA'd the board and tried again the next day.
In my ignorance, I repeated the same installation process as before thinking the problem was probably a faulty component on the previous board or some freak electrostatic discharge event. Much to my chagrin, as the GPU's mounting bracket grazed the same group of components on the way to its proper mounting position behind the board - again, millimeters away from the place the I/O bracket is actually supposed to go, maybe less - I heard to same loud "POP" cascade through the speakers. Sure enough, booting into Windows confirmed that my audio was now gone on this board too.
At this point I had no idea what was going on. Maybe my secondary graphics card was somehow faulty, maybe it was incompatible with the board in some way. Then I decided to repeat the installation process to see if I could discover anything interesting. That's when I noticed the consistent pop and crackle produced when the GPU bracket touched the aforementioned cluster of components. Just for good measure (and FOR SCIENCE!), I poked them several times with the GPU bracket, which produced an absolute cacophony of noise. I figured the board was RMA material anyway, best to confirm the situation so I could report back to all you fine people on the interwebs.
Woooo boy! Confirm the situation it did!
Windows started with an absolutely hellacious screeching noise that then throttled back to a constant rumble as the PC idled. Not that it could do much more than idle, though, because dialog boxes were popping up constantly saying that just about every audio port on the board was activated/dis-activated simultaneously. Quite the show.
I've since purchased an Asus Sabtertooth Z77 which features the Thermal Armor. This is handy because it completely covers most of the components on the board. Guess what, the secondary GPU was installed without issue.
Now, before the hardware Nazis come out of the woodwork giving me the " IT'S YOUR FAULT FOR INSTALLING HARDWARE WITHOUT COMPLETELY UNPLUGGING AND DISCHARGING THE SYSTEM FIRST, DUMB@$$", I'd just like to say that: 1) This is my 4th build, I've never done that in the past, and I've never had this problem before. 2) Like it or not, people regularly don't fully disconnect their system from ac power before swapping hardware. Usually "off" means "off"3) I'm not aware of such precautions being stated explicitly in the owners manual. 4) I swapped secondary GPUs on my old x58 system in a similar fashion many times, all without incident. I even spoke to Asus tech support (after a 2 HOUR WAIT!) and the support agent didn't even think to ask if the board was still plugged in during install. He asked me if I forced it in, if I damaged any components in the process, then stated it was likely an unfortunate ESD event.
Here's my counter-argument: If an experienced computer geek like me can mess this up - TWICE -, pity the poor n00b putting together his or her (but let's face it, probably his) first SLI rig. I say, as a manufacturer, if you have a design involving components that will cause irreparable damage to the board if shorted - even while the system is powered down - and these components MUST be placed mere millimeters away from each other, and they MUST be placed in a location that will likely be trafficked by large, awkward, unwieldy, conductive pieces of computer hardware...you know what, PUT A FRIGGIN PLASTIC CAP OVER THEM. Spring the .025 cents per board and save a lot of people a lot of potential problems.
So, Asus P8 series motherboard owners, be super careful. Sorry about the book.