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Power Supply And Video Card Poblems

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  • Graphics Cards
  • Power Supplies
  • Graphics
  • Product
Last response: in Graphics & Displays
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December 4, 2008 10:15:29 AM

I have recently gotten a new video card, an ati 3850 agp, and my old 250w power supply could not handle the load. So I purchased a 500w ozc ps, however after I installed it my computer would not boot past the POST screen. It would not even power a very basic configuration of the motherboard, video card and hard drive. So I sent it back and ordered a Cooler Master 500w power supply and it did the same thing, so I am starting to think it is not the power supplys. My motherboard is from 2002 and the rest of my computer is older as well, is there compatabilty issues between old parts and a new ps? If so which power supply is recommended for my system?

120 gb AtA hard drive
1.5 gb DDR ram
Pentium 4 northwood 2.8 ghz.
Ati HD 3850 agp
2 dvd drives

More about : power supply video card poblems

a b U Graphics card
December 4, 2008 11:03:13 AM

I don't think you will have a compatibility issue with that PSU as power is power. As long as the connections fit it should be fine. I don't mean to be insulting but did you remember to connect the 4pin power to your CPU as you have a Pentium 4? If you have then unplug everything from your mobo and re-connect it all again. Failing that reset you BIOS by removing the CMOS battery for 20mins, or using the jumper setting. Let us know how you get on. Good luck.
a b U Graphics card
December 4, 2008 11:05:29 AM

Forgot to ask but have you tried putting your old video card in just to elimate a video card issue?
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a b U Graphics card
December 4, 2008 11:25:02 AM

The older PCs powered their chips by connecting them directly to voltage rails provided by the PSU. But the newer PCs started putting DC/DC converters onto the motherboard which took a voltage provided by the PSU and efficiently converted it into the lower voltage needed by the chips. Many of the early DC/DC converters converted 5 volts into the lower voltage. Presumably this was because the power supplies of the time delivered most of their power on 5 volts. But converting 12 volts instead of 5 volts makes the wiring much simpler because a higher voltage delivers the same amount of power by using a smaller current. Smaller current lets you use less wires and connectors to deliver the same power. Power distribution is much easier at higher voltages. The highest voltage provided by a PC PSU is 12 volts so that became the most common input voltage used by the biggest DC/DC converters. A modern CPU has its own converter on the motherboard which converts 12 volts to whatever voltage the CPU requires. Modern video cards also have their own converters on the card which convert 12 volts into the desired voltages. The CPU and video card tend to be the biggest consumers of power, when fully loaded, so a modern PSU has to provide most of its power at 12 volts. So in the old days you had a bunch of chips directly connected to 3.3 or 5 volts and that's where a PSU provided most of its wattage. But in a new computer the PSU provides most of its power at 12 volts and then various DC/DC converters throughout the computer convert it to whatever voltage is needed by that particular set of chips. The table below is a more modern 480 watt PSU. The maximum power available on 3.3 and 5 volts has increased a little but the bulk of the expanded wattage is provided on the 12 volt rail.

http://www.playtool.com/pages/psurailhistory/rails.html

Try to match or exceed the rails of the old power supply.
December 10, 2008 6:52:20 PM

Thanks for the help guys
Unfortunatley I have managed to fry my hard drive and motherboard, but the power supply works fine in my brothers computer so he let me use his. But now Im searching for motherboards. Does the LGA 775 support my P4, it says it does but im not sure. any recommendations for a good hard drive?

http://www.newegg.com/Product/Product.aspx?Item=N82E168...
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