Is your problem caused by your PSU?

Author Svet on 24 February, 2012 | Print | Bookmark
Welcome to the forum! If you are having a problem, this is probably the best place to come to! But BEFORE you post with your troubles, make sure first you have read the Forum Rules, and the Suggestions to Posting And Getting Better Answers stickies.

Now, the most common problems we see here in the Forums are those relating to your Power Supply Unit (PSU). That metal box with wires coming out of it is far more important than you think. Especially when it comes to upgrading a PC.

You may have had a case which came with a PSU that was fairly cheap, and the board and CPU you had previously may have run with no problems at all. But then the time comes when you want to upgrade that mobo and CPU, and thats when the problems start....

"Hi, I just upgraded to a K7N2 Delta 2 board, but when I power on the system, I cannot run the CPU at its correct FSB!"

"I just put together a system based around KM4M-V board with Athlon XP3000, but the fans spin for a second and then stop..."

"I've replaced my old Geforce 4 MX440 with a Geforce 7600GS, but there are dots and lines all over the screen"

"i installed Windows fine on this KT6 Delta board, but when I try to run any 3D games the system just completely locks up..."

A lot of people at this point have already decided that its MSI's fault, and that they make "rubbish" motherboards. But they have failed to consider the one piece of hardware that often gets overlooked...


The Power Supply Unit. The often overlooked PC hardware

"So what do I need?"
Most modern mobos utilise two power connectors, the standard 20pin ATX connector that all boards need, and an auxiliary 4pin connector known sometimes as JPWR1 or ATX2. This connector provides a seperate 12v supply for the CPU, as most modern CPUs draw heavily on this power line.

If your power supply doesn't have this 4pin connector, then you may as well throw it away now and get a new one.

Secondly, you need to assess the specs of your PSU. There is another sticky here which warns of Q-Tec PSUs not correctly advertising their specs, which goes into more technical detail, but basically there is more to a PSU than the output given in watts, eg 300w, 420w, 550w. A good quality 380w PSU can be much better than a poor 550w one, that is why we ask you for the make of your PSU.

PSUs supply power to your system through several "rails", the most important being the 12v, 5v and 3.3v ones. The current supplied through these rails is measured in amperes (amps), and is usually listed on the sticky label on the side of the PSU, similar to the pictures shown below:

  
Two very different PSUs. The one on left has poor 12v rail and will cause problems. The one on right is much better![/i]

If your board has this 4pin connector, then you need a modern PSU which has an emphasis on the 12v rail, as this supplies most of the power to your CPU, graphics card, hard drive(s) and CD/DVD drives. For a basic SocketA board, such as KM4M-V, 15a should be sufficient, whereas a performance board such as KT880 or K7N2 Delta2 will need 18a or more. AMD64 boards have greater requirements, especially if you are running a dual-core CPU with two graphics cards in SLI; refer to their forums for specific advice.

If your board doesn't have a 4pin connector, such as KT3 or KT4 series, then your PSU should be a slightly older type, where the power balance favours the 3.3v and 5v rails. 12v rail on these boards is used to power motors in drives and fans, etc. As 3.3v and 5v are essentially drawn from the same source in ATX PSUs, you will never get the total output you see listed on the label together, which is why you must also consider the "Max Combined Output" of the 3.3v & 5v rails


"But it worked fine on my old system!"
Older PSUs were designed for older mobos, which mainly drew on the 5v and 3.3v rails to power the CPU and other onboard devices, leaving the 12v rail to power drive motors in HDDs, CD drives and floppy drives. As newer CPUs become more power hungry, the mobos become more reliant on a 12v supply to "feed" the CPU, so older PSUs cannot cope with extra demands.

So technically yes, your PSU may have been well able to cope with your previous hardware configuration, but now you have upgraded, it could simply be that your PSU is not able to supply correct power demands of your new mobo...


"So is my PSU any good?
Unfortunately, there doesn't seem to be any hard set guide to what amps to look for in a PSU to power a certain mobo/CPU combination. You can browse through the forum, and there are many suggestions what to look for.

If you want to ask for help, then please avoid people asking the same questions again, and tell us the specs of your PSU: list the brand, theoutput in watts, and the amp ratings on the 12v, 5v and 3.3v rails. Saying you have a 420w PSU is irrelevant, as there are better quality 360w PSUs, than some cheaper 550w models. We want to see: "My PSU is a Codegen 350w (3.3v/20a, 5v/30a, 12v/12a)", not "My PSU is 500w". If you provide this information, you will get better and faster advice. Just supplying a make and model name and expecting users to search the internet to find your PSU specs is just a wee bit rude, as they are already giving up their time to help you!


How can I test if my PSU is causing the problem?
Try another better PSU. See if you can borrow one off a friend. Maybe you have another computer at home? Either way, there is no point trying a PSU that is the same or weaker than the one you already have.

Also just because a PSU works on another computer, doesn't automatically mean it will be powerful enough for yours. Don't forget, a PSU that works on a PIII system probably won't work on a new Athlon XP system. 

If you do decide you want to buy a new power supply, then do all your homework first. Compare prices and specs, and look for reviews. But don't trust all reviews! Not everyone tests PSUs properly, some will rate PSUs if they have a shiny gold finish and a fancy LED, without even glancing at the performance.

When shopping for PSUs, either online or in a store, are the specs available? if not, then visit the manufacturer's website. You could spend $/£100 on a flashy PSU with six fans and rainbow LED lights (Wink) but it could be worse than yours. A good quality PSU could last you for years, and maybe another couple of upgrades. Don't spend more than you can afford, but don't skimp on the specs at all costs.

If you plan on doing more upgrades, it would pay to invest in a very good high quality PSU, that way you know it will last through your next upgrades. Buying a PSU now that just meets your requirements may cause problems if you upgrade a lot of hardware later, then your new PSU is once again not powerful enough.


"OK, so my PSU is rubbish, what do you recommend?"
I recommend you read through the following threads: 






also browse through some threads, you will see many problems caused by poor PSUs, and many suggestions on what to get!

the following article appeared in Custom PC magazine in November 2004 and is very good reading, plus you can see results of the 12 PSU's they tested:

Custom PC - "I've got the power" - Nov 2004
Custom PC PSU labs test

UPDATE:

CustomPC's 2005 Labs Test, 29 PSUs tested:
http://www.pcpro.co.uk/custompc/labs/26/psus/products.html

(please note a free registration is required after you view a few pages)


Good luck! biggthumbsup

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Category: Retired motherboards

Last updated on 24 February, 2012 with 4211 views