Intro
There are multiple pieces of software that show you the voltages on your 3 main voltage rails that exist on all ATX PSU's (+3.3V, +5V and +12V), such as Speedfan, Everest, BIOS etc., but those are very unreliable and it has been proven in the past, and by not knowing the actual voltages you can put your system in danger, its even worse for those who adjust their rail voltages accoring to software readings.
What now?
You need to have a voltmeter or a multimeter, if you don't have one, buy it, they are pretty cheap.
So you've got a multimeter, you ready to see your real voltages?
You are about to do this while your computer is ON, only do this if you know how to deal with electricity. If rails are shortend, you could damage your PSU and components, this is only a guide so I don't feel responisble if something goes wrong. Proceed with caution.
First you have to set up the multimeter to read the voltages you'll be measuring, there should be a dial on the multimeter, move it to number 20 (like this) in the section represented with this symbol.
Insert the black probe into the COM plug on multimeter, red probe should go in voltage detection plug, DO NOT insert the probe into current detection plug (on cheaper multimeters it usually has a 10A max label).
Turn OFF your computer and locate a free 4 pin molex and a free AUX connector, make sure they are fully accessible for the probes on your multimeter, if they're not, do some cable rearrangement.
Measuring
Time to start. You want to observe these 3 voltages in all states. So you will have to set up the probes before you turn the computer ON, mainly because you want to observe the:
- Post
- Boot
- Windows startup
- System at idle
- System at load
- Shutting down
This way you can see how your PSU acts under different levels of load.
The picture below shows what's the ideal minimum and maximum voltage on PSU rails.
If your PSU falls close to minimum ATX spec or fluctuates alot even within ATX specs, I suggest replacing it, but that's just my opinion.
12V RAIL MEASURING
Find a 4 pin molex connector and insert the red probe into the yellow 12V connector while black goes into any black ground connector.
5V RAIL MEASURING
This is almost the same as measuring the 12V rail, red probe goes to red 5V connector and black probe of course in any black ground connector.
3.3V RAIL MEASURING
For this you need an AUX connector, red probe goes to one of the two orange 3.3V connectors while black probe goes to any of the black ground connectors.
Results
So what did you find out? Is your current PSU better than what it used to say using software? Post your wrong/correct voltages.
I hope this guide has been helpful, please contact me if you find any errors, or if you need more info, I'll edit the post.
PSU Calculator
There are multiple pieces of software that show you the voltages on your 3 main voltage rails that exist on all ATX PSU's (+3.3V, +5V and +12V), such as Speedfan, Everest, BIOS etc., but those are very unreliable and it has been proven in the past, and by not knowing the actual voltages you can put your system in danger, its even worse for those who adjust their rail voltages accoring to software readings.
What now?
You need to have a voltmeter or a multimeter, if you don't have one, buy it, they are pretty cheap.
So you've got a multimeter, you ready to see your real voltages?
You are about to do this while your computer is ON, only do this if you know how to deal with electricity. If rails are shortend, you could damage your PSU and components, this is only a guide so I don't feel responisble if something goes wrong. Proceed with caution.
First you have to set up the multimeter to read the voltages you'll be measuring, there should be a dial on the multimeter, move it to number 20 (like this) in the section represented with this symbol.
Insert the black probe into the COM plug on multimeter, red probe should go in voltage detection plug, DO NOT insert the probe into current detection plug (on cheaper multimeters it usually has a 10A max label).
Turn OFF your computer and locate a free 4 pin molex and a free AUX connector, make sure they are fully accessible for the probes on your multimeter, if they're not, do some cable rearrangement.
Measuring
Time to start. You want to observe these 3 voltages in all states. So you will have to set up the probes before you turn the computer ON, mainly because you want to observe the:
- Post
- Boot
- Windows startup
- System at idle
- System at load
- Shutting down
This way you can see how your PSU acts under different levels of load.
The picture below shows what's the ideal minimum and maximum voltage on PSU rails.
If your PSU falls close to minimum ATX spec or fluctuates alot even within ATX specs, I suggest replacing it, but that's just my opinion.
12V RAIL MEASURING
Find a 4 pin molex connector and insert the red probe into the yellow 12V connector while black goes into any black ground connector.
5V RAIL MEASURING
This is almost the same as measuring the 12V rail, red probe goes to red 5V connector and black probe of course in any black ground connector.
3.3V RAIL MEASURING
For this you need an AUX connector, red probe goes to one of the two orange 3.3V connectors while black probe goes to any of the black ground connectors.
Results
So what did you find out? Is your current PSU better than what it used to say using software? Post your wrong/correct voltages.
I hope this guide has been helpful, please contact me if you find any errors, or if you need more info, I'll edit the post.
PSU Calculator
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