Thursday, August 03, 2006

ATX PSU Diagnose

By leorick  |  8/03/2006 07:35:00 PM 11 comments

About ATX Power Supply

ATX Power Supply converts the wall (AC) to the direct current (DC) needed by the PC. The power supply looks like a metal box with fan. Typical computer power supply generates the voltages needed by the computer motherboard accessories. [Read more...]

Before Everything

Disconnect all socket from your main board, HDD, CD/DVD drive, Floppy drive and etc so that we can isolate which part is not working.

Step 1 - Check Wall AC power

To check this, you may try to plug in any electrical appliances to the wall socket to verify that the 240V exist such as lamp, table fan or etc. If it is working, that mean the power from the wall socket is ok. You may also check the voltage with multimeter if you have one.

Step 2 - Power Socket Fuse

If you are using power socket with fuse, you may try to check this first. The method is to plug the other end to other appliances such as your printer (turn on to verify), monitor (turn on and look for LED indicator) or rice cooker (My rice cooker using the same type of socket). Same thing, if it is ok, we know up to the power cord is also ok.

Step 3 - Voltage Selector

Not all power supply have this switch. My place using 240VAC. So if it accidentally set to 110VAC the power supply maybe burn out. No more further troubleshooting. But at place with 110VAC, maybe it will not burn out when it accidentally set to 240VAC. It will in the low voltage condition and may not start I presume. Select the correct voltage according to power provider rating.

Step 4 - 5V+ Standby Voltage


The first point that have voltage upon plug in the AC power is the standby voltage.[refer figure above] 5VSB constantly provides 5V power to the connector at pin 9. Check this voltage using volt meter to make sure that 5V exist (while the AC is turn on).

Step 5 - Simulate Power On

Now is the interesting part. To turn on your ATX power supply without mother board, the way is to make contact between pin 14 and ground pin(3,5,7,13,15,16,17). Meaning you can turn it on by connecting pin 14 with the only green wire connecting to it to other ground pin that is the pin with black wire. To verify that the power supply is working, the ventilation fan should be working split second after you connect pin 14 to ground. Paper clip would be the best choice.

Step 6 - Check All Output

Now you can check all voltage output from the power supply. You need a voltmeter in order to do that.

Pin Name   Color Description
1 3.3V   Orange +3.3 VDC
2 3.3V   Orange +3.3 VDC
3 COM   Black Ground
4 5V   Red +5 VDC
5 COM   Black Ground
6 5V   Red +5 VDC
7 COM   Black Ground
8 PWR_OK   Gray Power Ok (+5V & +3.3V is ok)
9 5VSB   Purple +5 VDC Standby Voltage (max 10mA)
10 12V   Yellow +12 VDC
11 3.3V   Orange +3.3 VDC
12 -12V   Blue -12 VDC
13 COM   Black Ground
14 /PS_ON   Green Power Supply On (active low)
15 COM   Black Ground
16 COM   Black Ground
17 COM   Black Ground
18 -5V   White -5 VDC
19 5V   Red +5 VDC
20 5V   Red +5 VDC

Good Luck


Kevin said...


Al said...

Pretty cool! I actually did a case mod that allows me to get at the power from the PC that sits by my lab bench:

Anonymous said...

Ive done this before & found that i need to load the +5V before the psu will work normally. If not either it didnt fire up or the voltages were low. I used a 6v motorcycle headlamp.

I made 3.3 V adapter using your instruction. Here is the link:


Kool, I've done it and my question follows,....
I read about other articles related to 'Power up atx psu without motherboard', and from this link:

he mentiond: "Make sure you don’t leave the power supply running without a load, because it will overheat and smoke will start to rise. You should be very careful while working with an atx power supply because there are high voltages and currents going trough that thing, and you don’t want to get yourself hurt. So don’t underestimate electricity, because it can kill you."

Do I have to add a lod to the atx psu, if yes where?


leorick said...

If you want to measure the voltage accuracy;


If it doesn't turn on and you know the PSU is okay;

The answer is yes, but I never came across good condition PSU that won't turn on when I connect the green pin to the black pin before.

How to load it? You may load it with a bulb, cooled power resistor or etc
Read here for more information

Hi Leorick,

What I meant was if I short the green line to Ground that would switch on the ATX psu, can I leave it on like this without any load?


Yes, but maybe for a short while, 2,3 minutes.

what I enjoyed most was the blog that put amperes table not imagine how much needed to complete my paper in college!

Any normal load on the power supply will work, im not a fan of loading with a led light, not enough current really, just plud a old hard disk into one of the power plugs

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