Tom wrote:
> Hi,
>
> I have a P4C800-E Deluxe motherboard and plan to upgrade the GFX card to
> a AGP HD3850, currently I have a AIW 9800 Pro installed. Currently the
> case has a Antec True430 power supply and I'm concerned whether it will
> be big enough to handle the new GFX card. The True430 has a max +12
> rating of 20 amps. The power supply calculators that I've used thus far
> indicate that the power requirements for the entire system to be 400
> watts with a 80 percent load. This includes selecting the HD3850.
>
> I've also read conflicting information about the -5 volt line on the
> P4C800-E Deluxe motherboard's 20-pin connector. Supposedly this will
> determine whether a modern power supply can even be considered. I've
> looked through the owners manual and could not find any information
> other then the -5 volt line is listed, but not if it's required.
>
> Can the P4C800-E Deluxe motherboard use a modern power supply? And if
> so, which one would you recommend?
>
> I would be most interested if someone is already using a P4C800-E Deluxe
> with a HD3850 GFX card. Perhaps you can share your experience?
>
> Thank you.
>
12V @ 5.90A CPU P4 2.8 Northwood
0.43A fan
0.77A regular 9800Pro Aux connector (3DMark)
0.6 A hard drive
Total 7.7 A
3.3 @ 13.75A Powers the memory and chipset
5V @ 0.56A Very little 5V motherboard load
5.5 A regular 9800Pro Aux connector (3DMark)
1.0 A Hard drive
1.5 A CDROM with no media present
Total 8.56A
5VSB @ ?? Not measured. Will substitute boilerplate ~1A
-12V @ ?? Not measured. Probably powers the GD75232 RS232 chip.
-5V @ ?? Not measured, and not an easy way to tell if the
board depends on this or not. My PSU does have a -5V output.
Total power estimated based on my P4C800-E system is
3.3*13.75 + 5*8.56 + 12*7.7 + 5VSB*1 = 45.375+42.80+92.4+5 = 185.6W
The HD 3850 measurements are here. The AGP version would add to this,
a few watts for Rialto bridge.
http://www.xbitlabs.com/articles/vid...0_5.html#sect0
A ballpark figure is 12V @ 5A, so your total system power hasn't gone up
that much (part of the 9800Pro loading is bundled into the 3.3v motherboard
rail), but more of the load would be on +12V. Somewhere around 12A
total load on the +12V, with the new card present. Now your +5V
rail is quite unloaded, and could be down to a couple amps.
http://www.xbitlabs.com/images/video...power_full.png
So it would appear you're still safe (under the 20A).
*******
This assumes your power supply is healthy. I opened up my
True 480 the other day, to discover bad caps on the output
rail side. The primary was in good shape
(because otherwise, it would blow up).
The brown deposits are just like the picture here.
http://upload.wikimedia.org/wikipedi...4/PSU_Caps.jpg
I didn't touch anything in there, just had a look before removing
the supply for good. I heard arcing sounds coming through the
computer speakers, so the bad caps wouldn't have lasted much
longer. I also has the machine reboot, when returning from sleep
one day, which means the supply wasn't stable at first power
up.
I don't know of a reason why that motherboard would use -5V.
A tiny, tiny amount of current would flow, because the -5V
is connected to the hardware monitor chip. But whether they
tied -5V into any of their opamp circuits, is an unknown.
If it did turn out to be a problem, it can be fixed for a
couple bucks. You can buy a 7905 three terminal regulator,
a couple bypass caps, and solder that right to
the motherboard. The 7905 could accept the -12V from
your new supply, and then make a regulated -5V from it.
By soldering it to the motherboard, you avoid the need
to add a pin to the Mini-Fit main power connector (on
the power supply side).
http://www.fairchildsemi.com/pf/LM/LM7905.html
The circuit to use is Figure 6 on page 12. "Input" would
be the -12V pin on the main power connector. "Output" would
be the -5V pin on the main power connector. And the
circuit could only be left in place, if a power supply
*without* -5V on it was being used. If you put a supply
*with* -5V on it, the circuit should be removed (or rather,
the connection to -5V should be broken). Placing a small
switch in the -5V path, would be another feature you could
add. The TO-220 package would not need a heatsink on it,
if the -5V isn't drawing any power. If you tried to
draw 1 amp from the 7905, without a heatsink, it would
rapidly overheat and shut off its output. So my
assumption here, is there is no significant load.
http://www.fairchildsemi.com/ds/LM/LM7905.pdf
I use a similar 7812 based regulator here, to run fans or a small
12V video camera from, and that regulator is bolted to
a small 2"x2"x1" heatsink. It runs from an unregulated
transformer based DC wall wart (about 17VDC).
Paul
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