how to use a multimeter?

[IvanI]

Hello!

I just bought a multimeter for the purpose of testing my power supply (I got a new GFX card, and I want to see how the PSU is handling it...)
But... I don't know how to use a multimeter to measure voltages and amperes in my computer (CPU, GFX, PSU, etc..)
is there some guide here on the forum or on the net or if someone can write something about it here?

Have mecy,

- mulimeter n00b

 

[Hades16x]

Are you asking how to use the device or where to touch the prongs to, to give you a reading?

I'm under the assumption that most places that test power handling measure it at the wall. The only place I could think on a graphic card is to touch the metal wires carrying the power from the external power plug to the PCB. You can touch the + line (red) to the ground line (black) and it MAY give you a reading.

I'm also assuming GFX cards that have external power plugs ALSO use power from the motherboard, can anyone verify? PCI-e is what 75watt? and a 6 pin is 150w or something?

Like I said most people test wattage at wall. They test wattage of system sans extra hardware, and you get a value, then they add new hardware in such as a graphics card and it reports a new, higher value. Subtract the take the absolute value of the difference and that is the amount of power that the new hardware consumes.

 

[Technophobe]

Only test AC power (from the wall) if you know what your doing (by the sounds of it you don't). Don't mess with AC.

Testing internal PC voltages is pretty safe for you but not for the PC if you slip and short pins out. Usually multimeter probes have very long exposed metal probes on the end, these give lots of opportunity to short things out. If you just push the probes into the areas where the wires go into the connectors, your fairly safe.

If your measuring voltages on points on the motherboard etc. my advice is to use insulation tape to tape up all but the very point of the metal probes.

Make sure you have the meter set for reading voltage, not current. Start by setting the meter for a much higher voltage range than what you expect and then swicth down to a lower one.

As the last poster said, black is usually the negative side.

Testing current is a totally different story and you need to either have a special meter that can sense current by a clamp around the wire (usually expensive) or by breaking the connection between the wire / connector and device and putting the meter in-line with the wire. This can get very messy. Again, unless you are confident and really need to, don't go there either.

 

[Uberbob102000]

Only test AC power (from the wall) if you know what your doing (by the sounds of it you don't). Don't mess with AC.

Testing internal PC voltages is pretty safe for you but not for the PC if you slip and short pins out. Usually multimeter probes have very long exposed metal probes on the end, these give lots of opportunity to short things out. If you just push the probes into the areas where the wires go into the connectors, your fairly safe.

If your measuring voltages on points on the motherboard etc. my advice is to use insulation tape to tape up all but the very point of the metal probes.

Make sure you have the meter set for reading voltage, not current. Start by setting the meter for a much higher voltage range than what you expect and then swicth down to a lower one.

As the last poster said, black is usually the negative side.

Testing current is a totally different story and you need to either have a special meter that can sense current by a clamp around the wire (usually expensive) or by breaking the connection between the wire / connector and device and putting the meter in-line with the wire. This can get very messy. Again, unless you are confident and really need to, don't go there either.

QFT! So some n00bies know what they are doing.

 

[Brain_ReCall]

Can you mention what model you have? That will give us an idea of its capabilities. Like Technophobe mentioned, measuring current is not recommended, even if it allows that much current. Average handhelds usually have two current terminals, something low like 100mA, and a higher one, like 1A or 10A. They're usually fused, so if you try too much current on it it won't explode or burst into flames (exaggeration on that last bit ).

If your multimeter has separate probes with several sockets for them, the black one will always go in the black socket, usually labeled "Common." There are usually two or three other sockets. One will be for Voltage/Resistance, the others for some amount of Current. For now, just put the red probe in the Voltage/Resistance socket.

For standard 12V/5V, use the 4-pin molex connectors. Jam the black probe into the hole for one of the ground wires (black). Set the multimeter to a DC voltage setting higher than your trying to read. For example, if you want to read the 12V (yellow), and your multimeter reads 2.5V, 10V, and 20V, set it to 20V. If you try the lower ones it'll probably say "OL" standing for overload. It won't hurt it, unless its something really excessive that you shouldn't be poking at. If it reads a negative number, you probably got the probes backwards. Jam the red probe into the hole for the yellow wire for 12V, red for 5V.

Reading the other voltage rails (3.3V, 5Vsb, -12V, etc) and the SATA connectors are much more difficult and not suggested.

Here's what a quick Google search pulled up: http://www.overclockers.com/tips1248/