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How do I test a PSU with a volt meter?

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December 27, 2010 12:47:07 AM

Can anyone provide pinout guides for ATX 20 & 24 pin? I'm don't know the ATX versions but what I'm looking for is a guide to which wires carry which voltage.

Thanks!
The Ozz!

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a c 275 ) Power supply
December 27, 2010 12:51:50 AM

http://en.wikipedia.org/wiki/Atx#Power_supply
Yellow = +12V
Red = +5V
Green = Power_On
Purple = +5VSB
Orange = +3.3V
Blue = -12V
Black = Ground

You can either probe a molex, or back probe the main atx connector, if you want to test the PSU with no load you can do it as shown in this video, but readings will likely be fairly different once its under full load.
http://www.youtube.com/watch?v=5FWXgQSokF4
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December 27, 2010 1:07:04 AM

I assume for it to be under a load it would have to be on. Right? Can I leave out the the Green and Purple? I don't know what they mean.
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a c 275 ) Power supply
December 27, 2010 1:10:27 AM

By under load i mean hooked up to the motherboard with the system powered up and running an intensive task. The purple powers your motherboard components when the system isnt on so that one isnt too important, the green one, when shorted to ground, tell the PSU to start up, as shown in that video.

The only 3 you need to test are yellow to black, red to black, and orange to black, i would test them with your system on and idling, and with your system at full load.
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December 27, 2010 1:36:03 AM

hunter315 said:
By under load i mean hooked up to the motherboard with the system powered up and running an intensive task. The purple powers your motherboard components when the system isnt on so that one isnt too important, the green one, when shorted to ground, tell the PSU to start up, as shown in that video.

The only 3 you need to test are yellow to black, red to black, and orange to black, i would test them with your system on and idling, and with your system at full load.


That's kinda what I thought but just needed a confirmation. I tend to doubt myself more than I should. The problem I'm having is a non-booting system going to BSOD before the OS starts to load, assuming. In my research of troubleshooting, the PSU is the first and most likely piece to go which can cause BSOD's etc. I will run a Memtest86+ v4.10 to check the RAM and go from there. I'm just in the preliminary phases of this situation and don't know more than that.

Thanks for your help. Much appreciated, friend!

The Ozz
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a c 144 ) Power supply
December 27, 2010 2:48:20 PM

Measure between the colored wires and either chassis ground or the black wires. Yellow wires should be 12 volts. Red wires: +5 volts, orange wires: +3.3 volts, blue wire : -12 volts, violet wire: 5 volts always on. Tolerances are +/- 5% except for the -12 volts which is +/- 10%.

The gray wire is really important. It should go from 0 to +5 volts when you turn the PSU on with the case switch. CPU needs this signal to boot.
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a b ) Power supply
December 27, 2010 3:18:32 PM

If you can boot to BIOS and not get a BSOD and or the system stays powered up long enough to check voltagesI would forgo the paperclip to power on the system. Also verify temps in Bios if you can (verifies the HSF is properly working.

Have you looked at Health page in bios. Look at voltages and temps (for temps leave system at health page for approx 10 min). If these are good then I would procede to memtest from bootable disk and voltage readings using the DVM.

For the +12 and +5 voltage readings, as indicated in other posts, check at Molex connector. For voltage checks at the 20/24 pin connector and the 4/8 ATX connector (when mated)I use a straight pin (With care) as the probes for the DVM.
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a b ) Power supply
December 27, 2010 11:37:02 PM

My comment was based on being able to power-up, in which case he does not need to short the two wires. He indicated that the system would power on, but was getting a BSOD prior to loading the operating system - Reason I asked if he could get into BIOS. If the system will stay powered on while in Bios the voltage at the molex will be present.
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December 28, 2010 1:17:59 AM

RetiredChief said:
My comment was based on being able to power-up, in which case he does not need to short the two wires. He indicated that the system would power on, but was getting a BSOD prior to loading the operating system - Reason I asked if he could get into BIOS. If the system will stay powered on while in Bios the voltage at the molex will be present.


You are correct. There were voltages present at all the connectors and they appear to be within the tolerances. I'm fixing to Memtest86+ 410 it for a pass and see what we get. Then I plan to use the Ultimate Boot CD to test the HDD and board, if it'll let me. From what I understand there's a slew of useful tools. If they come up clean then I guess its time for a reinstall.

Thanks
The Ozz
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a b ) Power supply
December 28, 2010 1:48:29 AM

You run Prime-95 and measure voltage with CPU stress to 100%

You run furmark and measure voltage with GPU stress to max

These are one of possible conditions to measure PSU voltages and loaded conditions.

The other option is run high performance games to stress the CPU and GPY then measure the voltages.
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a b ) Power supply
December 28, 2010 3:22:54 AM

Did temps also indicate ok.

The most common cause, if voltages and temps are OK are the memory and a problem with the HDD. You didn't indicate if you were trying to Load win 7, or an earilier version of Windows (vista or XP). Win 7 has a very good at loading the drivers needed for newer MB (Only have had to use the old "F6" load for an SSD with the intel AHCI driver. If it's vista or XP you may need to load a driver during instal.

Once everything is up and running, download CPUID HWMonitor and prime 95. Prime 95 is better for detecting memory problems than memtest (MY oppion). Monitor voltages and temps while running it (You should get close to max temps within about 10->15 min. This primarily loads the +12V. Furmark is great for checking GPU and provides a heavier load on the +12 V depending on the Graphics card installed (What leon2006 indicated in his post.
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December 28, 2010 12:36:16 PM

RetiredChief said:
Did temps also indicate ok.

The most common cause, if voltages and temps are OK are the memory and a problem with the HDD. You didn't indicate if you were trying to Load win 7, or an earilier version of Windows (vista or XP). Win 7 has a very good at loading the drivers needed for newer MB (Only have had to use the old "F6" load for an SSD with the intel AHCI driver. If it's vista or XP you may need to load a driver during instal.

Once everything is up and running, download CPUID HWMonitor and prime 95. Prime 95 is better for detecting memory problems than memtest (MY oppion). Monitor voltages and temps while running it (You should get close to max temps within about 10->15 min. This primarily loads the +12V. Furmark is great for checking GPU and provides a heavier load on the +12 V depending on the Graphics card installed (What leon2006 indicated in his post.


I'm sorry. It's a Compaq with XP, an AthlonXP 3000+ and 512RAM (It's not my main PC, FYI). With such a restricted BIOS it told me only the CPU temp which was 53C, normal for such a tiny heat sink, assuming. I ran a dskchk /r, it did find and fix some errors. Now, I plan to clone the disk or at least the recovery partition, since the bad sectors have been reallocated, then try a fixmbr cause the fixboot didn't help and since there were other partitions from the manufacture I didn't want to chance corrupting them all without a clone.

BTW, It's not BSOD'n anymore, it's stuck in a loop rebooting at the XP loading screen.

Thanks guys!
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January 6, 2011 11:21:09 PM

Best answer selected by ozzman24.
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a b ) Power supply
January 7, 2011 6:02:30 AM

This topic has been closed by Maziar
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