Update 12/30/2020: Asus has opened a new webpage that you can use to see if your motherboard is impacted by the failures. You can find the webpage here.
Last week widespread reports of melting MOSFETs on Asus' Z690 Hero motherboards emerged across various social media platforms, with pictures of motherboards that met a fiery fate spurring a bit of investigation from the enthusiast community. We followed up with Asus to learn more, and the company acknowledged the issues to Tom's Hardware and provided a full statement on the underlying causes (below). The company is also beginning a recall/replacement program for impacted users, but that will take some time to come into effect. If you have a Z690 Hero, be sure to read our outline below that tells you a few ways to determine if your board is impacted — if it is, you should stop using it right away.
Interestingly, YouTuber Buildzoid's theory of the root cause was correct (more on that after the statement). It all boils down to a capacitor that Asus inadvertently installed backward. Here's Asus' statement:
"To our valued ASUS Customers, ASUS is committed to producing the highest quality products and we take every incident report from our valued customers very seriously. We have recently received incident reports regarding the ROG Maximus Z690 Hero motherboard. In our ongoing investigation, we have preliminarily identified a potential reversed memory capacitor issue in the production process from one of the production lines that may cause debug error code 53, no post, or motherboard components damage. The issue potentially affects units manufactured in 2021 with the part number 90MB18E0-MVAAY0 and serial number starting with MA, MB, or MC.
You can identify your part number by referring to the product packaging:
As of December 28, 2021, there have been a few incidents reported in North America. Going forward, we are continuing our thorough inspection with our suppliers and customers to identify all possible affected ROG Maximus Z690 Hero motherboards in the market and will be working with relevant government agencies on a replacement program. Thank you so much to everyone for your patience and support while we are working through the replacement program.
If you have any questions or concerns please feel free to contact ASUS customer service. Best regards, The ASUS Team."
After widespread reports of the issue washed over various enthusiast forums and Reddit, YouTube Buildzoid performed his own analysis, which you can see in the video below.
In short, all of the impacted motherboards had one commonality: two burned-out MOSFETs that are responsible for providing 5V power to a number of components on the motherboard, including the power delivery subsystem for the DDR5 modules.
Buildzoid correctly surmised that the issue didn't stem from the MOSFETs, but rather the capacitor right next to them. Comparing pictures of the impacted motherboards to fully-functioning boards reveals the capacitor is installed backward, thus reversing polarity and leading to the MOSFET failures.
If you own an Asus Z690 Hero and aren't aware of the batch number, you need to check the capacitor that you see circled in the image above (it is between the DIMM slots and Q-Code reader). If the "150" is aligned upside down, it is best to stop using the motherboard and contact Asus customer support.
It's encouraging to see Asus step up and acknowledge the issues quickly and take steps to begin a replacement program immediately. We're told that Asus is working with the Consumer Product Safety Commission (CSPC) to label the replacement program as an official recall, at which time users can begin the replacement process. We'll update you as more details become available.