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Possible PS issue....?


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#1
brettt777

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I am about to upgrade my Dell XPS 710 with a QX6700 Extreme CPU, a couple more GBs of DDR2 and an 8800 GTX (I can get all of that for about $250 so it's worth it to me). The reason all this started was because the original 8600GTS went south, at least that's what it appeared to do. Now, I have been a technician of one sort or another for over thirty years so I am sure I could figure this out on my own but I thought I would ask on here to save myself the trouble. The 8600 GTS had issues, so I replaced it with the only thing I had available; the Radeon X300 out of my daughters old desktop. Nowhere near suitable for any kind of gaming but at least it gives me a picture, works fine, system runs all day long. The 8600 of course, had to have a power connector plugged in to operate, the 8800 GTX also needs this (possibly two), the X300 does not. If there were some kind of power supply issue that caused the 8600 to fail, it would cause problems with the rest of the system, would it not? What voltages are on the video card power connector besides +/- 12 and 5 vdc? All of those are used elsewhere in the PC, correct? I don't want to invest in some components to upgrade this thing if there might be a PS problem.
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#2
Digerati

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Well, as a long time technician, I always want to confirm I am supplying good, clean, stable power myself. So you really need to verify you have a good supply with sufficient power.

The 8800 GTX certainly has a greater power demand than the 8600. You did not state specifics but note this 8800 GTX recommends, as a minimum, a 450W supply with 28A on the +12V rail.

Note that a graphics card can easily be the most power hungry device in your computer. The PCIe connector has +12V and +3.3V and both are used elsewhere. But depending on how it is distributed and isolated has an impact on how it affects different components in the computer.

Here is my canned text on testing PSUs:

To properly and conclusively test a power supply unit (PSU), it must be tested under various realistic "loads" then analyzed for excessive ripple and other anomalies. This is done by a qualified technician using an oscilloscope or power analyzer - sophisticated (and expensive) electronic test equipment requiring special training to operate, and a basic knowledge of electronics theory to understand the results. Therefore, conclusively testing a power supply is done in properly equipped electronic repair facilities.

Fortunately, there are other options that are almost as good. I keep a PSU Tester in my tool bag when I am "in the field" and don't have a good spare power supply to swap in. While not a certain test, they are better than nothing. The advantage of this model is that it has an LCD readout of the voltage. With an actual voltage readout, you have a better chance of detecting a "failing" PSU, or one barely within specified ATX Form Factor Standard tolerances. Lesser models use LEDs to indicate the voltage is just within some "range". These are less informative, considerably cheaper, but still useful for detecting PSUs that have already "failed". Newegg has several testers to choose from. All these testers contain a "dummy load" to fool the PSU into thinking it is connected to a motherboard, and therefore allows the PSU to power on, if able, without being attached to a motherboard - great for testing fans, but again, it is not a true load or suitable for conclusive testing.

Note the required voltage tolerance ranges:

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Swapping in a known good supply is a tried and true method of troubleshooting used for years, even by pros. If you have access to a suitably sized, spare power supply, carefully remove the suspect supply and replace it with the known good one, and see if the problem goes away.

I do not recommend using a multimeter to test power supplies. To do it properly, that is, under a realistic load, the voltages on all the pins must be measured while the PSU is attached to the motherboard and the computer powered on. This requires poking (with some considerable force) two hard and sharp, highly conductive meter probes into the main power connector, deep in the heart of the computer. One tiny slip can destroy the motherboard, and everything plugged into it. It is not worth the risk considering most multimeters, like plug-in testers, do not measure, or reveal any unwanted and potentially disruptive AC components to the DC voltages.

Note the ATX Form Factor standard does not "require" specific color coding for power supply connector wiring. It has recommendations but manufacturers often do not follow them. Sadly, many testing guides or tutorials will refer to wire color only and that can lead to improper testing.

The voltages can be checked in the BIOS Setup Menus of most motherboards but they do not reveal ripple or other anomalies either. And of course, booting into the BIOS Setup Menu requires a working PSU.

As always, before working in the interior of the computer case, take necessary ESD precautions to ensure static buildup in your body does not discharge through and destroy any sensitive devices. Unplug from the wall and touch bare metal of the case before reaching in. And remember, anything that plugs into the wall can kill. Do not open the power supply's case unless you are a qualified electronics technician. There are NO user-serviceable parts inside a power supply. If you do not have a tester or a suitable spare to swap in, take the PSU to a qualified technician for testing.

For more information on testing PSUs, see this excellent article by Gabriel Torres, Why 99% of Power Supply Reviews are Wrong.


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#3
brettt777

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My PS is 750 watts. According to the eXtreme Outer Vision power supply calculator, what I need for my system with the upgraded CPU and GPU is just over 600 watts so I should be fine. I have some test equipment that I can use to monitor power under load. I may plug the 8600 back in just to see if there is something happening with a high demand GPU plugged in. Obviously the X300 doesn't put near as much of a load on the power supply.
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