Man of Honour
There have been quite a few PSU problems recently, so i compiled this for myself but thought I'd share it. Hope it helps.
(If there is anything I've missed or that needs adding, let me know)
Checking your Power Supply Unit
Your expensive components are reliable on one common source, the power they receive. So it’s important that your power supply is working and functioning as expected.
Safety first! Yeah?
Firstly, if you suspect your PSU is faulty, then never try to repair it. You need specialised equipment to ensure that the PSU is discharged of all its stored electricity. It’s therefore recommended to replace failed PSUs rather than try and fixing them.
What does the PSU actually do?
In basic terms, a PSU regulates and delivers power to the system and its components. It’s responsible for converting incoming AC (Alternating Current) in to three DC (Direct Current) voltage supply lines. These three lines are better known as “rails”.
The three rails supply 12volt, 5volt and 3.3volt to the system and are responsible for providing suitable power requirements for specific components. The 12volt rail, for example, supplies power to the motherboard, graphics card, CD and HDD drives etc. whereas the 5volt and 3.3volt rails supply power to other onboard devices.
Power supplies are often rated by the amount of power output in Watts and these range anything from 250w to a whopping 1100watts (even more for servers). The wattage is calculated by multiplying the supplying voltage by the amperage of the component. So, you have to know what each component draws in amps and the voltage of the line it’s on. For example, a motherboard that takes 5AMPS on a 5Volt line requires 25W. By adding all the components up, you’ll get any idea of how much power you’ll need. So basically, the more components you have in your system the bigger PSU in Watts you need.
Of course, it would be stupid to even consider doing this so thankfully there are PSU calculators around if you’re unsure as to what wattage PSU you need (links below maybe useful). However, the general rule of thumb is to always have more than you need as this means that it won’t be running at full load and therefore increase its life.
PSU Calculators
http://www.extreme.outervision.com/psucalculatorlite.jsp
http://web.aanet.com.au/SnooP/psucalc2.php
PSUs conform to the ATX form factor and their have been many variants of throughout which is something to bear in mind when upgrading components, for example.
The biggest change that was introduced with the ATX PSU was the ability for the computer to be turned on and off via software. This is to say, that the PSU is not directly connected to the case power button but via the motherboard instead. Therefore, power is constantly being provided to the motherboard and most motherboards will show a light to indicate this.
Cables and connectors
The first thing you’ll noticed when pulling the PSU out of its new box or inside the case, is that there are loads of cables and connectors which may seem daunting at first. However, you will need to familiarise yourself which each cable and what they do.
Most of the cables are colour coded so you can identify the current they supply. So, the Yellow is +12v, Red is +5v, and the black is ground.
A typical ATX Power Supply Unit will normally comprise of:
• ATX 20/24 pin Molex Main Power Connector
24 pin was introduced as part of ATX2.0 Feb 2003.
Used to supply power to the motherboard.
• ATX 4 pin peripheral Molex 12V connector
Provides supplementary power for P4 motherboards. If your motherboard has this connector, it’s best to have it connected otherwise you will have stability issues.
• 8 PIN (P8) EPS12V connector (ATX2.2)
Provides supplementary power for motherboards that support dual core processors. If your motherboard has this connector, it’s best to have it connected otherwise you will have stability issues.
• 4 bin berg connector for the floppy drive
Used to supply power to small form units such as a floppy drive.
• 4 pin Molex
Provides both a 5volt and 12volt supply to components such as hard drives, CD/DVD drives, fans etc
• 15 pin Serial ATA connectors (ATX 1.3 in April 2003)
Supplies Serial ATA hard drives with the three different voltages; 3.3v, 5v and 12v. They are easily identified by being a wafer thin power connector which can easily fall out of the drive which is something to bear in mind. It is possible to use 4-Pin Molex adaptors, which drops the 3.3volt supply used by HDD for hot-plugging.
• 6 pin PCI-E connectors (ATX2.2)
A dedicated 12v supply for today’s demanding PCI-E graphics cards. You would normally expect at least two cables to support SLi configuration.
Today’s PSUs come with cables that are “Moduled”. This is to say, that you can connect only the cables you actually need, rather then having to find somewhere for the cables you don’t. This makes life a little simpler and tidier too.
So how do you know if it’s a failed PSU?
Not all problems are related to a failed or faulty PSU, but it’s best to eliminate the PSU when making your diagnosis.
Symptoms of a failed PSU include:
• No power to the System
• Periodically turns off
• Random re-boots meaning that the PSU is not providing enough power to keep it going.
• Noisy fan or failure. Some motherboards have a PSU fan detector and if the PSU is connected to this, the system will detect a PSU fan failure.
Things to check
1. Surely that’s obvious
It sounds obvious but the first check is to make sure that the PSU is plugged in at the wall and switched on. Don’t laugh, it does happen. Make sure the switch on the back of the PSU is also on. You might want to check fuses as well.
2. Check the motherboard
Most modern motherboards have an LED that indicates that power is reaching the motherboard. Check that this is on. If it’s not on, then check that the 20/24 pin connector is securely in its place on the motherboard. If you have an 8pin EPS12v connector on your motherboard, make sure the 8pin cable is also securely connected. If this doesn’t solve your problems, you need to read on.
3. Fasten everything
Your next step is to check that all your power leads are securely fastened and are where they should be. Check the physical condition of the cables for anything obvious like a broken cable.
4. Can it cut it?
If you’ve been upgrading your system and neglecting the PSU, it could be that the existing PSU isn’t up for the job. Check that PSU is suitable and supplying the required wattage as described earlier. Use the PSU calculator to check this. If this is the case, then you might have to invest in a more powerful PSU.
5. Getting serious
The next thing is to check that the PSU is supplying the correct voltages. Of course, it’s unrealistic to expect your PSU to be supplying spot on voltages as described earlier. They key is to have stable voltages within an allowable tolerance. So, you will have to allow for some deviation of around 5% either side of the expect rails. So for 5volts you need to allow between +4.8volts and +5.3volts and for 12volts between 11.4volts and +12.6volts.
Anything outside this range is certain to be a problem with the power supply.
There are many ways to check the rails:
First option is to use the motherboards sensors which monitor the voltages as well as system temperatures.
The easiest method to access this information is through the system BIOS. Depending on the BIOS installed, there will be a menu displaying the voltages. It’s pretty basic and there are no legends of history, so you’ll have to keep a sharp eye on what going on.
Alternatively, there are plenty of software utilities which can read the same sensor information but instead can process the information in a presentable GUI. Most motherboards, such as the ASUS, come with their own utilities (Asus Probe) for diagnosing system stability and are excellent for showing the history of the rails across a period of time. You’ll soon be able to tell if the PSU is supplying incorrect voltages.
If however, your motherboard manufacturer does not provide such a tool, there are plenty of third party solutions such as Motherboard monitor, Everest, NestSensor etc to name a few. These are all capable of showing the stability of your PSU.
If however, your system is so unstable that you can’t get past POST, let alone into Windows, then it maybe time to resort to more traditional methods of using a multi-meter, which is explained in the next section.
6. Strip down the bare essentials
If you’re down to this step, then everything is working as expected; you’ve checked the cables, the connections, the voltages etc and still the problem hasn’t been determined. It’s looking more likely that it isn’t a PSU problem but you need to completely eliminate it first before looking else where. It’s time to take some dramatic steps.
Firstly, you can take out non critical devices such as sound cards, TV cards, NICs, CD/drives, floppy drive, USB devices, non essential fans etc. If you have more than one physical HDD, then detach these leaving only the boot HDD. Everything you can get away with basically. Then test.
If everything works fine, and works fine for a while under load, then it looks like one of those devices you’ve just removed is the route of your problem.
Add the items back into the system one at a time and test until all items are back. If it becomes unstable on re-instating one particular component, then you may have found your culprit or the PSU isn’t supplying the required wattage but you checked this earlier, didn’t you?
7. Swap out
The very last thing you can try to completely eliminate your PSU from the equation, is to swap out the PSU with a known working one. Of course this means having a spare PSU hanging around which is a luxury for most, but if your in the habit of building your own computers, it not such a bad idea to keep one floating around anyway. Very handy.
Conclusion
If the checks above found a problem with the PSU, then it’s most likely you’ll have to replace the PSU, either buy a new one or return to the manufacturer if its still in warrantee but hopefully, your problems will be over.
However, if the check proved that the PSU is working fine then you’ll have to start looking elsewhere but at least you’ve eliminated the power supply unit.
Using Multi-Meters to test your PSU
Firstly, remember that the Yellow cable supplies +12v, the red +5v, and the black is ground.
Don’t forget this.
Multi-meters are a good way of checking:
• AC voltage
• DC Voltage
• Continuity
• Resistance.
They typically consist of:
• Two probes. 1 positive (red) and one negative (black)
• Either an Analogue or digital display
• A switch for type of power test.
Power test for Power output
Turn PC off but leave plug connected.
Take power connector (Molex) and insert black probe into black wire connector.
Insert red probe into red wire connector.
Set multi-meter to 20volts and turn on PC.
Read out should be around +5volts.
Turn off PC and repeat process but this time connecting the red probe into the yellow wire.
Power PC on again and read the read out should give you around +12volts
Allow for some deviation of around 5% either side of the expect rails. So for 5volts you need to allow between +4.8volts and +5.3volts and for 12volts between 11.4volts and +12.6volts.
Anything outside this range is certain to be a problem with the power supply.
Measuring resistance (ohms)
Ensure there is no power supply. Unplug PSU completely.
Set the multi-meter to ohms and touch probes to test.
To test cable for example, place one probe into one cable (say pin 1) and the other into the other end. You should get a signal.
Measuring Voltage
When using a multi-meter, ensure that positive side of the multi-meter connects to the positive side of the target device and the negative side to the negative.
Set the multi-meter to “voltage” and when attached, you get a reading.
Broken cable? Set multi-meter to ohms.
Check battery? Set multi-meter to volts.
By Paul Hudson 21/07/2007
(If there is anything I've missed or that needs adding, let me know)
Checking your Power Supply Unit
Your expensive components are reliable on one common source, the power they receive. So it’s important that your power supply is working and functioning as expected.
Safety first! Yeah?
Firstly, if you suspect your PSU is faulty, then never try to repair it. You need specialised equipment to ensure that the PSU is discharged of all its stored electricity. It’s therefore recommended to replace failed PSUs rather than try and fixing them.
What does the PSU actually do?
In basic terms, a PSU regulates and delivers power to the system and its components. It’s responsible for converting incoming AC (Alternating Current) in to three DC (Direct Current) voltage supply lines. These three lines are better known as “rails”.
The three rails supply 12volt, 5volt and 3.3volt to the system and are responsible for providing suitable power requirements for specific components. The 12volt rail, for example, supplies power to the motherboard, graphics card, CD and HDD drives etc. whereas the 5volt and 3.3volt rails supply power to other onboard devices.
Power supplies are often rated by the amount of power output in Watts and these range anything from 250w to a whopping 1100watts (even more for servers). The wattage is calculated by multiplying the supplying voltage by the amperage of the component. So, you have to know what each component draws in amps and the voltage of the line it’s on. For example, a motherboard that takes 5AMPS on a 5Volt line requires 25W. By adding all the components up, you’ll get any idea of how much power you’ll need. So basically, the more components you have in your system the bigger PSU in Watts you need.
Of course, it would be stupid to even consider doing this so thankfully there are PSU calculators around if you’re unsure as to what wattage PSU you need (links below maybe useful). However, the general rule of thumb is to always have more than you need as this means that it won’t be running at full load and therefore increase its life.
PSU Calculators
http://www.extreme.outervision.com/psucalculatorlite.jsp
http://web.aanet.com.au/SnooP/psucalc2.php
PSUs conform to the ATX form factor and their have been many variants of throughout which is something to bear in mind when upgrading components, for example.
The biggest change that was introduced with the ATX PSU was the ability for the computer to be turned on and off via software. This is to say, that the PSU is not directly connected to the case power button but via the motherboard instead. Therefore, power is constantly being provided to the motherboard and most motherboards will show a light to indicate this.
Cables and connectors
The first thing you’ll noticed when pulling the PSU out of its new box or inside the case, is that there are loads of cables and connectors which may seem daunting at first. However, you will need to familiarise yourself which each cable and what they do.
Most of the cables are colour coded so you can identify the current they supply. So, the Yellow is +12v, Red is +5v, and the black is ground.
A typical ATX Power Supply Unit will normally comprise of:
• ATX 20/24 pin Molex Main Power Connector
24 pin was introduced as part of ATX2.0 Feb 2003.
Used to supply power to the motherboard.
• ATX 4 pin peripheral Molex 12V connector
Provides supplementary power for P4 motherboards. If your motherboard has this connector, it’s best to have it connected otherwise you will have stability issues.
• 8 PIN (P8) EPS12V connector (ATX2.2)
Provides supplementary power for motherboards that support dual core processors. If your motherboard has this connector, it’s best to have it connected otherwise you will have stability issues.
• 4 bin berg connector for the floppy drive
Used to supply power to small form units such as a floppy drive.
• 4 pin Molex
Provides both a 5volt and 12volt supply to components such as hard drives, CD/DVD drives, fans etc
• 15 pin Serial ATA connectors (ATX 1.3 in April 2003)
Supplies Serial ATA hard drives with the three different voltages; 3.3v, 5v and 12v. They are easily identified by being a wafer thin power connector which can easily fall out of the drive which is something to bear in mind. It is possible to use 4-Pin Molex adaptors, which drops the 3.3volt supply used by HDD for hot-plugging.
• 6 pin PCI-E connectors (ATX2.2)
A dedicated 12v supply for today’s demanding PCI-E graphics cards. You would normally expect at least two cables to support SLi configuration.
Today’s PSUs come with cables that are “Moduled”. This is to say, that you can connect only the cables you actually need, rather then having to find somewhere for the cables you don’t. This makes life a little simpler and tidier too.
So how do you know if it’s a failed PSU?
Not all problems are related to a failed or faulty PSU, but it’s best to eliminate the PSU when making your diagnosis.
Symptoms of a failed PSU include:
• No power to the System
• Periodically turns off
• Random re-boots meaning that the PSU is not providing enough power to keep it going.
• Noisy fan or failure. Some motherboards have a PSU fan detector and if the PSU is connected to this, the system will detect a PSU fan failure.
Things to check
1. Surely that’s obvious
It sounds obvious but the first check is to make sure that the PSU is plugged in at the wall and switched on. Don’t laugh, it does happen. Make sure the switch on the back of the PSU is also on. You might want to check fuses as well.
2. Check the motherboard
Most modern motherboards have an LED that indicates that power is reaching the motherboard. Check that this is on. If it’s not on, then check that the 20/24 pin connector is securely in its place on the motherboard. If you have an 8pin EPS12v connector on your motherboard, make sure the 8pin cable is also securely connected. If this doesn’t solve your problems, you need to read on.
3. Fasten everything
Your next step is to check that all your power leads are securely fastened and are where they should be. Check the physical condition of the cables for anything obvious like a broken cable.
4. Can it cut it?
If you’ve been upgrading your system and neglecting the PSU, it could be that the existing PSU isn’t up for the job. Check that PSU is suitable and supplying the required wattage as described earlier. Use the PSU calculator to check this. If this is the case, then you might have to invest in a more powerful PSU.
5. Getting serious
The next thing is to check that the PSU is supplying the correct voltages. Of course, it’s unrealistic to expect your PSU to be supplying spot on voltages as described earlier. They key is to have stable voltages within an allowable tolerance. So, you will have to allow for some deviation of around 5% either side of the expect rails. So for 5volts you need to allow between +4.8volts and +5.3volts and for 12volts between 11.4volts and +12.6volts.
Anything outside this range is certain to be a problem with the power supply.
There are many ways to check the rails:
First option is to use the motherboards sensors which monitor the voltages as well as system temperatures.
The easiest method to access this information is through the system BIOS. Depending on the BIOS installed, there will be a menu displaying the voltages. It’s pretty basic and there are no legends of history, so you’ll have to keep a sharp eye on what going on.
Alternatively, there are plenty of software utilities which can read the same sensor information but instead can process the information in a presentable GUI. Most motherboards, such as the ASUS, come with their own utilities (Asus Probe) for diagnosing system stability and are excellent for showing the history of the rails across a period of time. You’ll soon be able to tell if the PSU is supplying incorrect voltages.
If however, your motherboard manufacturer does not provide such a tool, there are plenty of third party solutions such as Motherboard monitor, Everest, NestSensor etc to name a few. These are all capable of showing the stability of your PSU.
If however, your system is so unstable that you can’t get past POST, let alone into Windows, then it maybe time to resort to more traditional methods of using a multi-meter, which is explained in the next section.
6. Strip down the bare essentials
If you’re down to this step, then everything is working as expected; you’ve checked the cables, the connections, the voltages etc and still the problem hasn’t been determined. It’s looking more likely that it isn’t a PSU problem but you need to completely eliminate it first before looking else where. It’s time to take some dramatic steps.
Firstly, you can take out non critical devices such as sound cards, TV cards, NICs, CD/drives, floppy drive, USB devices, non essential fans etc. If you have more than one physical HDD, then detach these leaving only the boot HDD. Everything you can get away with basically. Then test.
If everything works fine, and works fine for a while under load, then it looks like one of those devices you’ve just removed is the route of your problem.
Add the items back into the system one at a time and test until all items are back. If it becomes unstable on re-instating one particular component, then you may have found your culprit or the PSU isn’t supplying the required wattage but you checked this earlier, didn’t you?
7. Swap out
The very last thing you can try to completely eliminate your PSU from the equation, is to swap out the PSU with a known working one. Of course this means having a spare PSU hanging around which is a luxury for most, but if your in the habit of building your own computers, it not such a bad idea to keep one floating around anyway. Very handy.
Conclusion
If the checks above found a problem with the PSU, then it’s most likely you’ll have to replace the PSU, either buy a new one or return to the manufacturer if its still in warrantee but hopefully, your problems will be over.
However, if the check proved that the PSU is working fine then you’ll have to start looking elsewhere but at least you’ve eliminated the power supply unit.
Using Multi-Meters to test your PSU
Firstly, remember that the Yellow cable supplies +12v, the red +5v, and the black is ground.
Don’t forget this.
Multi-meters are a good way of checking:
• AC voltage
• DC Voltage
• Continuity
• Resistance.
They typically consist of:
• Two probes. 1 positive (red) and one negative (black)
• Either an Analogue or digital display
• A switch for type of power test.
Power test for Power output
Turn PC off but leave plug connected.
Take power connector (Molex) and insert black probe into black wire connector.
Insert red probe into red wire connector.
Set multi-meter to 20volts and turn on PC.
Read out should be around +5volts.
Turn off PC and repeat process but this time connecting the red probe into the yellow wire.
Power PC on again and read the read out should give you around +12volts
Allow for some deviation of around 5% either side of the expect rails. So for 5volts you need to allow between +4.8volts and +5.3volts and for 12volts between 11.4volts and +12.6volts.
Anything outside this range is certain to be a problem with the power supply.
Measuring resistance (ohms)
Ensure there is no power supply. Unplug PSU completely.
Set the multi-meter to ohms and touch probes to test.
To test cable for example, place one probe into one cable (say pin 1) and the other into the other end. You should get a signal.
Measuring Voltage
When using a multi-meter, ensure that positive side of the multi-meter connects to the positive side of the target device and the negative side to the negative.
Set the multi-meter to “voltage” and when attached, you get a reading.
Broken cable? Set multi-meter to ohms.
Check battery? Set multi-meter to volts.
By Paul Hudson 21/07/2007
