Trying to understand PSU rails

The ATX spec says ±5% of the voltage, so it *should* be between +4.75V and +5.25V - MBM gets a bit sensor-confused so double-check by rebooting and seeing the health status in the BIOS to be sure. I think you can re-configure MBM to see the correct sensor if some are flim-flammed. Check the vcore and mem voltages as well and see if they jive w/ MBM. Sometimes your mobo manufacturer's health monitor is more accurate, so it may be worth to install it as well - if for nothing else to compare to MBM...

The ATX spec actually says +/- 10%, but I agree with and use the 5% rule.

MBM was a good tool - when it was still being updated. It is no longer updated and can give innacurate readings - especially for modern mobos. I don't think his system would remain stable with a 5V rail that far out of spec, therefore I believe that he is getting bad readings.

I agree that a mobo provided utility is good for monitoring inside windows. Some of the most accurate readings will actually come from the BIOS, but they can be misleading. If you're in the BIOS checking voltages, then you are more than likely not stressing the system and under stress is where you want the PSU to remain stable. Do this to check out your system voltages.

1. Check your voltages in the BIOS.
2. Use whatever hardware monitoring utility your mobo mfr provides to check voltages when in windows. Log voltages at close intervals and run a stress test to see voltages while the system is meeting heavy demands. You want to see steady voltages supplied to the rig - large spikes up or down = bad.