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Some Asus Z690 Hero Motherboards Have Melting MOSFETs, Theory Proposed

Asus Z690 Hero With Blown Up MOSFETs
(Image credit: Asus - ROG Forums)

YouTuber Buildzoid from Actually Hardcore Overclocking believes he has figured out the root cause behind a recent spate of Asus Z690 Hero motherboard failures. If true, the issue is related to a single capacitor on the mainboard being installed backward at the factory. 

Reports of the Z690 Hero failures began around 10 days ago when @TheMaxXHD, @Duhjahno took to Reddit and the ROG forums to complain about their Z690 motherboards no longer booting. Other users also shared images of their motherboards, revealing a commonality between the failures: two burned-up MOSFETs near the Q-code reader and DIMM slots.

However, from what we're able to discern, not all Z690 Hero motherboards suffer from the issues. YouTuber JayzTwoCents notes he has used his Z690 Hero extensively for testing purposes and it has worked perfectly fine with no failures.

Buildzoidhas a theory as to why some Z690 Hero motherboards are dying and others are not: Pictures of the impacted Hero boards have two burned-out MOSFETs in between the Q code reader and DIMM slots to the very top right of the motherboard.

Those MOSFETs are responsible for providing 5V power to a number of components on the motherboard, including the power delivery system for the DDR5 modules. This is interesting because users that have the board failures report that the Q-Code reader spits out the number 53 when boot up fails. Code 50-53 for the Asus Z690 Hero indicates that memory initialization has failed. Presumably, this is the only reason why the board fails to boot.

From this info, one can conclude that the MOSFETs are dying because Asus either got a bad batch or because they are cheaply made components. However, Buildzoid believes the issue is not related to the MOSFETs, but rather the capacitor right next to the MOSFETs that assists them.

Z690 Hero With Burned Up MOSFETs

(Image credit: Reddit)

If you look closely at the image above, you can see the capacitor appears to have been installed backward. Of course, the backward text is a big giveaway, but Buildzoid notes that you can see the polarity stripe on the capacitor as well, which ultimately dictates if the capacitor is backward or not.

Having this specific capacitor backward on the Z690 Hero is bad — this capacitor is polarized, meaning it has a negative and positive connection. When backward, the capacitor causes the MOSFETs to get extremely hot, and could very well cause them to melt. 

For now, this is a working theory from Buildzoid and shouldn't be taken as fact. He says there's a chance Asus has another revision of the Z690 Hero where the capacitor is meant to be backward, but his educated guess seems plausible. Ultimately, the evidence for Buildzoid's theory is convincing because the image of every single dead Z690 Hero online appears to have this capacitor backward.

We'll have to wait for an official statement from Asus to see if Buildzoid's theory is ultimately correct. We've reached out to Asus and will update when we learn more. 

  • InvalidError
    Definitely looks like people in the supply chain failed to note or notice that capacitors on some reels were the other way around.

    In principle, this should have been caught by the pick-and-place machines' visual inspection. Parts markings and orientation verification have been around for a very long time.
    Reply
  • Alvar "Miles" Udell
    If not caught by automated means, it should have been caught by QC. The ironic thing is that ASUS is marketing an AI quality control inspector to prevent manufacturing errors like this without the need for human based QC.

    IoT Integrator | Powering the business behind the Internet of Things (theiotintegrator.com)

    ASUS Keeps an AI on Quality Control in Smart Manufacturing
    Automating quality control on production lines improves defect detection and ensures continuous operations. A customized automated optical defect detector leads one hardware vendor to build a software development kit to help system integrators improve their clients’ manufacturing processes.
    Reply
  • NightHawkRMX
    I am growing more and more confident that ACTUAL QC does not exist anymore for computer parts. Things like this make me more and more confident. The Acer monitors that explode promptly after being plugged in are another example. Shows they never even plugged them in at the factory.

    You can't just do a visual inspection of a PCB to see if something works or is even safe to operate.
    Reply
  • InvalidError
    NightHawkRMX said:
    You can't just do a visual inspection of a PCB to see if something works or is even safe to operate.
    Well, a backwards polarized capacitor can "work" for hours before blowing up depending on how high the reverse bias voltage is vs rating, chemistry, construction, etc. and wouldn't be caught by something like post-assembly bed-of-nails testing that only lasts a few minutes.
    Reply
  • Oaklanoc
    Mine is also backwards like the drawing, so far no issues though.......
    Reply
  • InvalidError
    Oaklanoc said:
    Mine is also backwards like the drawing, so far no issues though.......
    Point an IR thermometer at it if you have one. Backwards polarized capacitors usually get pretty hot pretty quick. SMD capacitors installed the right way around should be about the same temperature as the board around them since the bulk of whatever little heat they generate gets sunk into the board.

    If the capacitor's temperature is significantly hotter than everything else around it, then failure is only a matter of time.
    Reply
  • Alvar "Miles" Udell
    Oaklanoc said:
    Mine is also backwards like the drawing, so far no issues though.......

    If your motherboard serial number matches those in the recall you better send it back. Even if it is properly installed with proper polarity and just labeled backwards, it's technically illegal to resell it as it's a recalled product, plus there is no reason to chance it.

    Yes it's a pain in the butt to change a motherboard out and especially to be without a computer for a while if they won't cross ship, but there's no reason to take a chance on it, plus you can use the excuse to change cases or upgrade your cooler. To quote ASUS:

    The issue potentially affects units manufactured in 2021 with the part number 90MB18E0-MVAAY0 and serial number starting with MA, MB, or MC.
    Reply