Memtest freezing with hyperthreading

[Jeybit1910]

I'm trying to make sure some DDR3 I have is working properly, so I've been trying to test it with the latest version of Memtest86+ (which I think is V5.01, from about 2013 or 2014). I've been using a Sandy Bridge i3 which is a dual core with hyperthreading, and a Z77 motherboard, which I figure should probably be good up to 1866Mhz RAM speed. The test runs fine on default settings, which I gather only uses a single processor core. However there is a setting at the beginning to 'force hyperthreading' - but if I click this, the system always freezes just under 2 minutes in. I've been able to check with some other RAM and a different CPU (Ivy Bridge i3 with hyperthreading this time), and exactly the same thing seems to happen - everything runs fine on default settings for as long as I like, but as soon as I set it to force hyperthreading (which shows usage of up to 4 logical cores), memtest will freeze after just under 2 minutes - no matter which combination of RAM and CPU.

 

One RAM set is Crucial 1866MHz and the other is Corsair 1600MHz, and I set XMP, and make sure they are running at the correct speeds. Everything else is default settings, the PSU is comfortably over-specced for the setup, and nothing is overheating.

 

I also got hold of Memtest86 (non-plus), version ~4.3, which runs fine at default settings too. I don't think there's an option to force hyperthreading on that version of Memtest.

 

Can anyone suggest what the problem is here?