How to Check if a Computer SMPS/PSU is Working or Not

How to
ATX SMPS PSU

The personal computers at your office or  home  are  powered by electronic power supply units called Switched Mode Power supply (SMPS). Commonly known as Power Supply Units (PSU) this hardware converts  the input AC power to output DC  varying  with respect to voltage. Though there are PSUs available in different form factors, ATX is the most commonly available and used one right now.

Being the most vital part of  workstation its important that a PSU work continuously without any hiccups. Have you ever noticed a PC that restarts quite often or a PC that shuts down after a short duration without  you initiating it? Well chances are high that the SMPS/ PSU  is  faulty. The test or confirmation about the status of SMPS is a must before speculating on what might be the possible reason for PC failure. Here is how exactly you can confirm that.

Firstly,  make sure that  the power cord is detached from  PSU and then take out the unit from cabinet. You will notice a 24 pin main connector along with many other 4 pin peripheral cable connectors coming out from the PSU. Here is what you have to do next:

1) Take one among the 4 pin peripheral cable connector and you will observe a yellow, red and two black wires from it. The yellow wire being the 12 volt supply and black the ground, you must connect a 10 ohm /10 watts ceramic load resister across them.

4 pin SMPS peripheral connector

This is how a ceramic resistor looks like:

ceramic resistor

2) Connect the power cord to the PSU now and take the 24 pin main power cable connector to the motherboard. You will notice a green wire and few adjacent black wires. Power the SMPS/PSU now and short the green (pin 16) and black (pin 17) point using a jumper (wire) .

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24 pin SMPS power cable connector

If the PSU fan rotates you can 8o % confirm that the unit is functioning well. There are still chances that the PSU can be faulty which can be tested by checking the output volts at the pins. If the fan does not rotate then you must replace ( or repair ) the unit before trying to power your PC again.

Pin description of the 24 pin power cable connector is given below:

PinNameColorDescription
13.3VOrange+3.3 VDC
23.3VOrange+3.3 VDC
3COMBlackGround
45VRed+5 VDC
5COMBlackGround
65VRed+5 VDC
7COMBlackGround
8PWR_OKGrayPower Ok is a status signal generated by the power supply to notify the computer that the DC operating voltages are within the ranges required for proper computer operation (+5 VDC when power is Ok)
95VSBPurple+5 VDC Standby Voltage (max 10mA)
1012VYellow+12 VDC
1112VYellow+12 VDC
123.3VOrange+3.3 VDC
133.3VOrange+3.3 VDC
14-12VBlue-12 VDC
15COMBlackGround
16/PS_ONGreenPower Supply On (active low). Short this pin to GND to switch power supply ON, disconnect from GND to switch OFF.
17COMBlackGround
18COMBlackGround
19COMBlackGround
20-5VWhite-5 VDC  (this is optional on newer ATX-2 supplies, it is for use with older AT class expansion cards and can be omitted on newer units)
21+5VRed+5 VDC
22+5VRed+5 VDC
23+5VRed+5 VDC
24COMBlackGround

Data credit  : pinouts.ru

Hope this post helps you to test  computer SMPS next time you come across such a situation. Share your thoughts and do share if you liked.


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