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How to use multimeter to check your voltages and rails!

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fwiw i use a 5 dollar multi meter i got on ebay its pretty accurate
 
Be very careful not to try measuring the rails with the meter set to amps! With the cheap non CAT rated meters, doing so will result in the meter leads instantly melting and possibly giving you a nasty burn. (Been there, done that, still have the scar and that was many years ago when a typical PSU was only 250W.) Go for at least a CAT II meter for PC use, but I highly recommend CAT III or CAT IV if you think you might work on automotive circuits or large UPSes in the future. (Also note that the newer CAT III and CAT IV meters come with probes that only have a little bit of exposed metal to avoid short circuits, which is very useful on anything.)
Just want to add for those who don't know. Do not use any thing but a digital mm. A reg cheapo needle type mm may cook components.
An analog multimeter won't bother power supply rails, though it can (but very unlikely) damage really sensitive circuits. But it would be mostly useless for precision measurements anyways, so I highly recommend a quality digital meter with DSP. ( http://www.refrigeration-engineer.c...200-Why-you-should-not-buy-a-cheap-multimeter )

And for measuring current, you can't beat a Hall effect clamp meter. (Very few conventional multimeters can measure the current a modern GPU draws and they'll introduce too much resistance.) Just clamp the probe around the wires for the rail you want to measure. I recommend the Radio Shack 22-172, which can also be used as a regular multimeter and it has a CAT III rating and a DSP. For $60, you'd be hard pressed to find a better deal. (Those who really need accurate measurements should still go for Agilent, Fluke, or Gossen.)
 
A halfway decent multimeter will have a fuse on the amp measurement setting.
That said, you should indeed have the thing set to measure volts if you're measuring volts.

Even an inductive clamp won't correctly measure GPU wattage, GPUs get a fair bit of their power from the PCIe slot. To do it right you need custom hardware.
Not that this thread is about power draw.
 
And any decent meter would have a CAT rating. (Except, of course, those made before the CAT rating system was invented. In that case, a used meter made by a trusted company like Fluke or HP would still be good. But check to make sure the previous owner didn't just bypass the fuses!) Also beware that the cheap multimeters generally use glass fuses (low breaking capacity) or no fuse at all. If you accidentally connect that meter set to amps across a supply capable of a lot of amps (car battery or even a large PC PSU), the fuse might simply arc through like a welding torch instead of properly blowing. Some higher end Fluke meters would beep if the probe is left in the current jack when set for voltage and the Gossens would even prevent you from turning the knob to voltage unless you first remove the probes.

Good point about the power coming through the PCIe slot, I work at a company that makes server network cards and they use special interposers with built in shunts (shunt directly on the interposer = minimal resistance) and some networkable Agilent multimeters to measure power. But even a high end network card uses very little power compared to even a low end GPU. A modern GPU is going to draw most of its power from the 6 pin or 8 pin connectors.
 
Modern GPUs run the first (and sometimes second as well, and/or memory and/or PLL1 and/or PLL2) phase(s) from PCIe generally speaking. It(the first phase) is the phase that is active at idle, as well as being the most heavily loaded phase during most operations.
GTX480/580s draw enough off the PCIe slot to torch the ATX24P connector if you're OCing heavily and have a couple GPUs. That's what all those supplemental power connectors are for on motherboards.

Having accidentally tested glass fuses on dead shorts across automotive batteries an embarrassingly large number of times (24 year auto mechanic, here. Among other things), I wouldn't worry about that "issue".
 
I have not read all of everything in this thread...are you testing the PS under load?
(test with computer running)

I was recently testing UPS batteries while being watched by someone who does not understand even as little as I know...under no load the batteries tested fine (good voltage) but when put under load they showed less than 1 volt....

I have built 24 VDC/VAC power supply for testing other equipment in the shop...
when set for DC it shows higher voltage with no load than when under load...
 
If you know it won't kill the computer, test it while powering the computer.
If you don't know if it'll go on a killing spree, test it on the bench :D
 
With a sata power cable you can test the 12V, 5V, 3.3V lines
it would be less draw than plugging in a fan. I see your point
about killing something with an unknown Power supply(newtoyou/pull etc?)
 
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