What readings to look for in a volt meter?

[Peaks]

I posted in the overclocking section of this forum about my system randomly rebooting because I initial thought it was a problem with my overclock (Q6600 with a B3 stepping, poor overclocker).

I was advised to run prime95 stress tests again to ensure my oc was still stable and to run memTest. I was also advised to use a volt meter to see what power my PSU was drawing as apparently random rebooting is a characteristic of a failing PSU?

I have run prime95 (about 12 hours) which passed, I have run memTest on both DIMMs (7 passes each) which passed. I have a volt meter but I am not sure what readings I should be looking for, could anyone help me with this?

I am runnign vista Ultimate 64-bit, rest of my stats are in my sig.

 

[aziraphale]

Forget the thing about measuring the power your voltmeter draws. It's important that the voltages on the other side are looking alright. (And anyway; if you don't know how to handle a voltmeter just forget about measuring around on the high voltage side of your PSU; You or your voltmeter will regret it)
You can measure the 12 and 5 volt (yellow and red against black) rails while your PSU is running...

 

[jsc]

If you have a multimeter, you can check all the outputs from the back of the main power plug - carefully, carefully.

Yellow wires should be 12 volts, red 5 volts, orange 3.3 volts, blue wire -12 volts, purple wire is the 5 volt standby (always on). The gray wire is really important. It sends a control signal called something like "PowerOK" from the PSU to the motherboard. It should go from 0 volts to about 5 volts within a half second of pressing the case power switch. If you do not have this signal, your computer will not boot. The tolerances should be +/- 5%. If not, the PSU is bad.

 

[Peaks]

ok thanks for the explanation. I have a power and energy monitor that reads watts, volts, amps, Hz etc is this what you mean by a multimeter?

So how do i check these? Do I unplug from the PC and just leave the rail I am checking plugged in?

 

[Paperdoc]

The meter you describe sounds like it can do the job - all you need to use is the Volts function, set to the appropriate range. jsc gave you all the colors and expected voltages, but did not mention that the common reference point is the black wires that are "0 volts". So on the voltmeter you connect the "common" or "-" lead to that black wire (there are several, all the same), and use the "+" lead to connect to the other colors. EXCEPTION: if you have a modern meter it may handle negative voltages easily and just show you a "-" sign on the digital display. But for meters without this feature, to measure the -12v (blue) one you must reverse the connections: meter Common or "-" goes to the blue wire, meter "+" goes to black.

jsc said to access all these at the back (exposed) side of the large main power supply connector on the mobo. The connector body is designed with plastic that prevents easily touching the metal contacts inside, so you need some long thin probe tips to reach in. Your existing metal probe tips may be good enough. Just be very sure that you don't let the probe tips touch anything else besides the particular contact point you want - shorts for even a fraction of a second could damage you PSU! For what you are doing you may well want to make a semi-permanent connection so you can watch the meter over a time period while carrying out "normal" work. So you will need a way to stick the probe contacts in and leave them there, and make sure they do not move - falling down from gravity and vibration can also cause a short circuit! For this, I suggest you shut off your system, remove the cover and make secure connections to the two wires (say, red and black), then re-start. You may or may not want to semi-replace the case cover during the test.

My meter's probe tips are not really thin so making a "permanent" stable hands-free connection like this is not possible directly. I use some extension wires with alligator clips on the ends. For each extension wire, one clip goes on the probe tip, and in the other I place a standard straight pin used for sewing etc. It's long, thin and sharp - easy to work into a tight space in the back of a power connector. With care you can establish good contact and a mechanically stable arrangement that prevents accidental shorts.