FreeBSD 6.1 problems on AMD64 Athlon 3800 - crashes from day1

[rondzierwa at comcast.net]

I read your email on the amd64 list, and have some experience that may help.

I have been upgrading my athlon boxes to amd64 by just changing motherboard, 
cpu and memory.  I have found, however, that many power supplies that work just
fine in other environments fail miserably when powering an amd64 machine under
both FreeBSD and Windoze.

After talking with several tech support people from both tyan and dfi, i did
some research. i found that most of the power supplies that i had been 
using did not meet the +12V requirements of the new cpu's i was trying 
to use.  This wasn't something i could measure using a volt meter, or 
even the onboard health monitoring hardware.  It appears to be some 
sort of transient "sag" in the +12V that is related to system loading.  High
performance video cards increase the load, and temperature seems to 
aggravate the problem as well.   

It was reccomended to me that the power supply should have more than 
one +12V regulator (or "rail"), and each one should be capable of supplying 
20 amps or more.  This specification is independent of the raw wattage 
value.  One power supply i was trying to use was rated at 550 watts, and it
 worked fine everywhere i used it, but it only had a single +12V regulator 
and that was only capable of 15 amps.  The amd64 rig would boot and 
install just fine, but when it was put under load (I was doing video editing, 
but its about as demanding on the system as a large compile), it would 
consistently lockup or simply reboot.   After trying several swaps (memory, 
disc, graphics card), i replaced the power supply with one that had dual 
25 amp +12V rails, and the system has run fine ever since.

I'm not saying this will solve all your problems, but its a simple thing to check.
Most power supplies have the amp ratings for each voltage on the label stuck
to the side of the unit.  If not, the manufacturer's website should have the 
information.  If you can't find the information anywhere, you probably got a
generic commodity power supply that most certainly is not up to spec and
should be replaced. 

good luck, 
ron.