Possible chassis fan issues

[TheStigsChineseCousin]

Parts list: https://pcpartpicker.com/list/pnrxtg

 

Today power flickered on/off a couple times, and my computer power cycled (yes, I know, a UPS is on my shopping list). After performing a normal shutdown and power on, I noticed something I'd never seen before, when I booted into Windows my rear case fan ramped down to 0 and stopped for a few seconds, then started back up again, and repeated this every 20-30 seconds. The front case fans stopped spinning entirely. CPU cooler fans on NH-D15 heatsink behaved normally.

 

Motherboard is an Asus Z370-F Gaming, BIOS version 0612, 3/1/2018. Rear fan is plugged in to Cha_fan2 header, front fans are on a splitter plugged in to M.2_fan header.

 

Steps I've taken to troubleshoot:

1. Full shut down and restart
2. Different PWM fan (used an extra NF-A14 I have), issue persisted
3. Stock 3 pin case fan, issue persisted
4. Different cables, issue persisted
5. Different fan headers on the motherboard, issue persisted
6. Switched from PWM to DC in BIOS, upon Windows boot, front fans stayed spinning normally at 60% as specified in the fan curve, rear fan stopped entirely.

In BIOS, the fans behave normally, no random stopping/starting, and they respond normally to any fan curve changes I set. The issues start upon booting into Windows. I am at a complete loss here, did the power cycle cause something on the motherboard to go wonky, or is this a Windows issue? Windows updated to 1803 a few days ago, but the fan issues just started today. Should I update BIOS? I've avoided this so far since I've always understood that if it's working or unless I need the functionality/bug fix of a specific update, I should leave it alone.

 

UPDATE EDIT: I've heard back from Asus, they advised to update BIOS. Before I do that though, I was reminded that Asus AI Suite does allow fan control from within Windows, so I will be installing that as well to see if issues can be resolved. Will update with findings later

 

[TheStigsChineseCousin]

RESOLVED: Installed AI Suite and set fan curves with that, let it sit in Windows for about 20 minutes and everything is functioning normally. If issues reappear first step will be resetting/updating BIOS, since this has led me to believe it was a BIOS bug.