Citation :
Power problems with AGP cards:
Until recently The 3.3 volts required for the AGP slot was taken from the
power supply's 5 volt line and regulated by the motherboard. The reason for
doing this was that the majority of power was used on the 5v and 12v
supplies and the 3.3v lines (which weren't very current intensive) would be
of a known stability rather than chancing the variable quality of different
brands of PSU. ABIT boards that use this system include LX6 and early
revisions of AH6.
Developments in the abilities of graphics chipsets have led to the
availability of more and more sophisticated display adapters. While this
may be good news in terms of speed, modern graphics chipsets require a lot
of power. A display adapter alone may now require in excess of 6 Amps. By
the time you've taken the 3.3v supplies on the motherboard, memory, CPU and
PCI slots into consideration, you can quite easily be looking at a 15A+ (33
Watt) drain, which is over what a fairly simple line regulator is able to
deliver. It is for this reason that the next stage in the evolution of
motherboard power supplies was to rely on the PSU's 3.3v supply until a
better alternative was found.
Both of the boards mentioned in the first paragraph can be modified to work
with modern AGP chipsets. The modification involves bypassing the
motherboard's regulation and using the 3.3v directly from the PSU.
Once this modification has been done the board stops having a problem, but
this may just shift the problem to the power supply. If the power supply
used is not able to give a stable 3.3v at the current the system will draw
then the PC will continue to crash. This is a more likely scenario with an
older rather than newer PSU. Apart from modified LX6s and AH6s, boards in
this category include BX6 (/r2), BH6, BE6, BP6, VA6, VT6x4, SL6 and SE6.
If your system proves to be incompatible with the PSU then there is
something that you must consider when choosing another PSU. A new PSU will
have a rating (in Watts) descriptive of how much power can be drawn from it,
but just because a PSU is rated at (for example) 300 W does not mean that if
you were not drawing any current anywhere else, you could draw 300 W from
the 3.3v line. Power supplies tend to be sold on an overall rating, i.e.
the manufacturer will take the power that the 12v, 5v, 3.3v, -5v and -12v
lines can each supply and add them together to give a figure for the maximum
power that the PSU could theoretically supply. You therefore need to look a
bit more closely at the power available at each output (some manufacturers
will quote this, others will not). If the maximum power available from the
3.3v line is not enough then the PSU will not drive your graphics card,
regardless of the overall rating of the PSU.
If you do need to upgrade your power supply we would strongly recommend that
you go for one which is ATX 2.03 compliant, which should be able to deliver
more current to the 3.3v output.
The latest stage in mainboard power supply design moves the 3.3v supply back
to being regulated from the 5v lines. The deployment of switching
regulation (or PWM) allows the board to monitor its own 3.3v output and
compensate for a high current drain reducing the 3.3v beyond an acceptable
tolerance. The BIOS' on our latest range of motherboards will even let you
set a voltage higher than the nominal 3.3v level to eliminate any chance of
a power drain affecting the AGP slot. This functionality is available on
BF6, BE6-II, BX133, KA7 (/100) and KT7 (/Raid).
Technical,
ABIT UK.
Also if everyone looks at their BH6 Manual, we have no way to adjust to 4x. This is taking straight out of the manual: "Accelerated Graphics Port connector supports AGP 1x and 2x mode 3.3V devices"
So I think the BH6 does in do need more power to run highend graphic cards. I feel (don't know if this is true or not) sense we can't change the 3.3v for the AGP slot, when the video card needs more power it takes it away from the CPU. So now the CPU voltage is down the AGP slot is also needing more power which causes all these lockups.
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