Which wire short for start the AT SMPS?

Answer 1

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.

This is how a ceramic resistor looks like:

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) .

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:PinNameColorDescription13.3VOrange+3.3 VDC23.3VOrange+3.3 VDC3COMBlackGround45VRed+5 VDC5COMBlackGround65VRed+5 VDC7COMBlackGround8PWR_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 VDC1112VYellow+12 VDC123.3VOrange+3.3 VDC133.3VOrange+3.3 VDC14-12VBlue-12 VDC15COMBlackGround16/PS_ONGreenPower Supply On (active low). Short this pin to GND to switch power supply ON, disconnect from GND to switch OFF.17COMBlackGround18COMBlackGround19COMBlackGround20-5VWhite-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 VDC22+5VRed+5 VDC23+5VRed+5 VDC24COMBlackGround

Data credit : pinouts.ru

Hope this post helps you to test computer SMPS next time you come across such a situation.