Sometimes machine won't start? PSU or motherboard?

NeilF · 28 Jan 2007 at 21:58

I have a friend with a PC where sometimes seemingly no matter how many times they press the on button the PC will not start. They then leave it/or disconnect/reconnect the power and there's a chance then it may start (then or later).

At first I thought it may be the power button, but there seems to be some eliment of having to just leave it, or disconnect the power and reconnect again involved.

So I'm guessing either PSU or MB?

My friend swears once, when they press the on button, and it failed to start, the lights did flick on. This is typical for example if you've not got the PC plugged into the mains but the PSU has a charge. What else can also give this behaviour? If something in the PSU is going? If something on the MB is going?

ps: The problem has progressively been getting worse - ie: The machine is harder and harder to start!

Thanks!

artaxerxes · 28 Jan 2007 at 22:00

How old is the Power Supply?

With the info given I would suspect that.

Try it with your power supply.

ghgh · 28 Jan 2007 at 22:00

Yeah it does sound like the power supply causing that problem, only way to test it if you havent got a psu tester or dont want to jump start it (not that I know how to) is to test it on another system and see if that fires up.

Could also be a cold boot problem, a BIOS problem or a motherboard fault IMO.

NeilF · 28 Jan 2007 at 22:03

artaxerxes said:
How old is the Power Supply?

With the info given I would suspect that.

Try it with your power supply.

Probably 4-5 or so years old (and a dirt cheap model)...

NeilF · 28 Jan 2007 at 22:04

ghgh said:
Yeah it does sound like the power supply causing that problem, only way to test it if you havent got a psu tester or dont want to jump start it (not that I know how to) is to test it on another system and see if that fires up.

Could also be a cold boot problem, a BIOS problem or a motherboard fault IMO.

My gut feel is PSU as well... I'm hoping someone can come along with some knowledge and say the symptoms don't sound like a feasible problem with the MB. ie: Therefore almost certainly pointing to the PSU.

artaxerxes · 28 Jan 2007 at 22:05

4-5 years old *cough*

Yeah - sounds like electrolytic decay in the PSU's capacitors. It loses 10-20% of its rated wattage year on year. So a power supply that was more than sufficient then will be borderline now.

ghgh · 28 Jan 2007 at 22:10

Yeah if the PSU is that old and has been powering a system it is very likely to be that, as they do deminish in power over time (at least cheapo psus do) ive seen some generic psus last a few months with overclocked systems and then litterally go pop with a bit spark inside the case.

Almost definitely the PSU but it 'could' be the motherboard, I wouldn't totally rule is out - do you have a differernt PSU you could test on that system - I wouldn't risk testing the suspected dead one on a decent system as it may take a component out if your very unlucky.

NeilF · 29 Jan 2007 at 10:10

artaxerxes said:
4-5 years old *cough*

Yeah - sounds like electrolytic decay in the PSU's capacitors. It loses 10-20% of its rated wattage year on year. So a power supply that was more than sufficient then will be borderline now.

Shhh!!!! My old system (P3-533) will hear you

NeilF · 29 Jan 2007 at 10:15

ghgh said:
Yeah if the PSU is that old and has been powering a system it is very likely to be that, as they do deminish in power over time (at least cheapo psus do) ive seen some generic psus last a few months with overclocked systems and then litterally go pop with a bit spark inside the case.

Almost definitely the PSU but it 'could' be the motherboard, I wouldn't totally rule is out - do you have a differernt PSU you could test on that system - I wouldn't risk testing the suspected dead one on a decent system as it may take a component out if your very unlucky.

But the question is, is this sort of fault possible on a PSU? Hard to get the PC started, but when it goes, it goes fine!

Is there a switch in the PSU to enable (full) power to the MB? If there isn't, and the switch in effect is on the MB to allow full power thru or not, then this is pointing more to the MB surely?

I've got an old Compax/HP mini PSU (250W)... I'll try that on my friends PC and see if it helps... It's a basic P4 machine with one hard drive and CD rom and nothing else, so 250W should be fine...

artaxerxes · 29 Jan 2007 at 11:27

The problem is getting progressively worse and occurs at startup - classic hallmarks of a PSU issue as we have discussed.

Disconnect some devices on the system and see if it boots more easily as the load drops below the Wattage Budget.

Look here and tally up

http://extreme.outervision.com/psucalculator.jsp

Make sure to add 50% for capacitor aging.

If it fails to boot up with the minimum devices then there is now some evidence that it is a motherboard fault.

Try it with your power supply as I said in the second post. If it fails to boot then there is now some compelling evidence for a mobo fault.

As it stands the most likely source of failure is the PSU.

Argue all you want - but do the testing.

NeilF · 29 Jan 2007 at 16:05

OK... Will test with my supply...

Just as long as there is in effect some sort of trip switch in the PSU that can get its knickers in a twist hence accounting for the problem...

As for your link... we're talking about a machine here that has a HD, CDRom and that's about it

artaxerxes · 29 Jan 2007 at 17:22

Don't test it with an ultra modern PSU if it is super old! I know that the Enermax Liberty ATX v2.2 should not be used with a system that has used ISA slots (Pre 1.3 specification).

Good luck!