I contacted Asus support who suggested doing a CMOS reset. I disconnected the power from the PSU, pulled out the CMOS battery for a good 15 minutes and held the power button for a minute to completely discharge the system. After placing the CMOS battery back in and plugging in the PSU I was then advised to change the following settings in the BIOS:
- BIOS > Advanced Menu > APM Configuration > ERP Ready: Enabled S4 + S5
- Restore AC Power Loss: Last State
After booting the system was stable. I ran the stress test from the Extreme Tuning Utility, Passmark BurnIn Test (with 100% load on CPU and RAM), and Prime 95's torture test. Albeit I let the tests run for about 15-20 minutes, but the system didn't crash; previously just being idle would just crash/BSOD. During the tests the ASUS AI Suite reported a CPU frequency of about 4.3GHz and the voltage fluctuated between 0.8 and 1.252 with an average CPU temperature of ~65c.
Feeling brave and confident (and perhaps a bit optimistic) I cranked up the CPU ratio to 50 (x100BC) on all cores. Again, I was stable running the same tests for about 15-20 minutes. The voltage was between 1.1225 and 1.341 and average CPU temperature was ~70c (Peak 80c). Again the system was stable.
I've also now enabled XMP for 3733MHz speeds from the memory to go with the 5GHz CPU speed and I'm stable. CPU temperatures are reasonable, ~70c, (peak 82c) during the same stress tests.
So it seems the reset of the CMOS seems to have done the trick. I can only presume the stock BIOS version screwed things up and a later fixed BIOS was unable to detect/rectify the problems in CMOS from a previous version.
The other settings (ERP and Restore AC Power Loss) feel innocuous.
Just wondering if anyone has any further thoughts?
Last edited by PeteJUK; 01-31-2020 at 02:40 PM.