RIP: Asus responds to its flaming motherboard

Asus has responded with a detailed report as to why its M3A-H/HDMI went up in flames and smoke. After publishing the first episode following the freshening smell of burnt electronics festered in our labs, Asus was keen to take the board back to Taiwan for further testing and let us know how it got on.


Here's its conclusion, with Asus' words and pictures (all we have done is tidy the English a little):
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Customer feedback to the damaged M3A-H/HDMI was a burnt out MOSFET.

Detailed information on the cause is in the statement below.

Backstory: The board was running fine with an FX62 for 9 months, then they dropped in a 9600 Phenom B2, without removing the motherboard or changing any other hardware and it firstly killed the Enermax PSU, they then replaced the PSU and the motherboard ignited within about 10 seconds.

Analysis:
1．Check the impedance of MOSFET Rgs. The test result is below. The normal Rgs is around 8K OHM and there is just VDD_NB high side MOSFET damage.

　 Phase 1 phase2 phase3 phase4 phase VDD_NB
High side Rgs (OHM) 8.16K 8.28K 8.2K 8.07K 12.7
Low side Rgs (OHM) 8.22K 8.25K 8.25K 8.16K 8.15K

2. Then we removed the VDD_NB high side MOSFET and re-check the impedance of PCB Rgs. The result is 8.05K OHM. This tells us that just MOSFET is damaged and the Driver function is OK.

3. Next we changed the MOSFET with good one and turn on the system. Then we checked the MOSFET gate waveform. According to the waveform all the function of VRM is still good.

CH1:VDD_NB High side gate
CH2:VDD_NB Low side gate
CH3:VDD_NB Phase node

VID=1V DC Load 0A




VID=1V DC Load 20A

Conclusion:
There is just VDD_NB high side MOSFET damage and it maybe caused by an abornal voltage or current spike. To determine the root cause we need the failed MOSFETanalysis report to help us find out. We have passed the failed part to vendor to do analysis so after receive the report we will update you again.