Before I progress I'd just like to say I am an IT consultant with over 12 years of PC building experience and amongst other things assisted Microsoft with troubleshooting WDM driver issues affecting Conexant TV tuner cards when Windows 98 came out. I am not a newbie, so please feel free to be over-technical.
I am currently tinkering with an MS-7046 motherboard with latest BIOS, and XP with latest Intel chipset drivers (and all others up to date).
If I boot the system up in DOS, Linux or XP (in safe mode) the CPU fan stays on at full speed and temperatures are fine. If, however, I boot into XP then as the startup screen appears the CPU fan slows down to a near-silent 788rpm (lord knows why that's the speed but this is what SpeedFan tells me and I've yet to find anything else that suggests it's not) and it stays in this "quiet" mode until I shut the machine down.
As long as the CPU is near-enough idle this is not a problem; the temperature of the processor (Intel Pentium 550) stays somewhere between 45 and 51 degrees C; perfectly adequate when playing movies, word-processing and the like.
If I put the CPU under >50% load though, the temperature gradually goes higher till the system panics and shuts down as the CPU exceeds 75 degrees. And the fan doggedly stays running "quiet" (ie slow) even though it's perfectly capable of speeding up under load.
I downloaded several fan monitoring tools (MBM and Speedfan for example) and all of them are reporting the temperatures the same, and I have even had some success with modifying the CPU fan to come on if the CPU load goes up - so clearly the functionality is there to do it. With these tools I can get the CPU fans to rev up if the temperature goes over 60, but they only do so for about a minute - something else seems to interfere with the process and slows the fan down again.
I do not have these third party utilities on the machine, and try something overly clever like playing Civilization 4, give or take half an hour my PC will throw a wobbler and shut down because the fan just won't speed up like it should.
MSI decided in their infinite wisdom to completely disable *all* the CPU temperature monitoring and control settings in the BIOS and render them invisible, but I manually enabled the "emergency shutdown temperature" option at 75 degrees using Modbin, and by some sheer fluke this actually works even though that setting is still not visible in the BIOS. This is how I know that if I leave Windows to manage the fan, only a keen bit of bios hacking is saving my CPU from reaching seriously high temperature.
I have replaced the HSF with a fairly decent cooler, and used Arctic Silver 5 for both the HSF and Northbridge coolers; these are not at fault.
I can only conclude that this is a Microsoft issue. So, questions:
1. Assuming it'll work would switching XP and the BIOS to non-ACPI mode ensure the fan runs at a sensible speed?
2. If so, would I be able to slow the fan down manually?
3. Any other ideas?