Any likely reason why a motherboard might be killing PSUs?

This is a bit of a problem - one PSU went down, so I put in another one and, blow me, that went down as well after a few hours' use.

The original one was a 680W Thermaltake PURE, the replacement was a Silenx 400W.

I don't want to go putting in another PSU and risk killing that until I can feel comfortable that this has just been sod's law at work. However, the Silenx 400W has proven itself very unreliable here - this is, I think, the third of three of them to go down (all used in different PCs) - though I blame myself for that, I was warned off them but took no notice!

Motherboard is an ASUS A8V Deluxe; CPU is an AMD Athlon 64 FX-55 with a Gigabyte 3D Cooler; and the graphics card is a Radeon X800 Pro 256MB.

The PC contains 2x SATA HDDs and one PATA DVD burner; plus four 80cm case fans (one of which is one the side panel and was not being used when the second PSU went down).

The PSU I have lined up to go in there is a 400W SilentQ; I think that's powerful enough but would appreciate hearing a team verdict on that, too.

TIA

Bob

Yes, there certainly are ways a motherboard could take a PSU down ..... but mostly, I wouldn't expect them to apply to good condition and well-made PSUs.

For a start, any switch-mode PSU is susceptible to burning out is left with power supplied but no load. It can happen in seconds. But ... if the PCs running, it isn't likely to be that, and besides, any PSU worth having has built-in protection against it anyway and if it detects no load, shuts itself down.

Or, if you have incrementally added lots of gubbins to the machine (extra hard drives, high-end graphics board, power-hungry video (as opposed top graphics) board, RAID board and so on, you could be drawing to much power and over-loading the PSU. It's not unknown for old PSUs to end up with melted leads or connectors from doing this. It doesn't sound like that's the case here, and any half-decent 400w ought to eat the load you mentioned comfortably.

Be aware, though, that not all 400w PSUs are born equal - though it sounds like you're already well-aware of that. :) The 400w on some cheapy supplies is highly speculative, and on some, it's even a peak rating not a continuous load rating. But it doesn't sound like the case here.

Or ... some components deteriorate over time. PSUs get hot, so when you turn on and turn off, components suffer a degree of thermal shock and, over time, break down. And if an old-ish PSU is heavily loaded, and not in good condition, then it could overheat and .... :(

Or, perhaps, if the voltage regulator on the motherboard is faulty, it's maybe drawing more on some lines than it should be.

Or ...... if the PSUs are getting on a bit, how clean are the fan blades? I've had more than one case where dust slows the fan down to the point where it can't cool the PSU which then rather inelegantly goes tits up. But, having cooled down, works again .... for a while. If the fan is visibly slow, or if the noise suggests speed fluctuation, then simply cleaning the dust and crap off the fan blades can resuscitate an PSU.

Trouble is, I can't think of any easy way to test what's going on without risking something getting damaged, unless you've got and are comfortable with using a meter. If you put another PSU onto that mobo, you risk the PSU and if you put another mobo onto one of the blown PSUs, you risk the mobo.

If you do have a decent volt/multimeter, you could connect the first 'blown' PSU to the 'suspect' motherboard, ground the negative probe on the meter to the chassis and test the voltages going to the mobo connector with it plugged into the mobo. You can usually get to the back of the connectors.

Obviously, I'd suggest you disconnect any hardware (hard drives, etc) you don't want to risk first.


Oh, and you do this at your own risk. I'm no expert, but I know enough to know what I'm doing if the gear's in front of me, but describing it in a post isn't easy.


WARNING - do NOT open the PSU up unless you're sure what you're doing. Some connectors will be live while the thing is connected to the mains and even the capacitors had hold a nasty belt.

Saracen,

Thanks very much for the pearls of wisdom.

I will, of course, be giving them due (and very serious) consideration - though would still welcome any further suggestions, tips, ideas about how to avoid killing any more PSUs.

I think I've had a similar thing happen with a cheap case - something to do with the earthing on the motherboard - or perhaps the case wasn't completely square - which may have warped the motherboard. I think it took the motherboard out with it as well. It was a while ago though so my memory is a bit fuzzy.

Have you got a decent case? Could the motherboard mountings be shorting somewhere? Check your motherboard cable connectors for power switch / speaker etc make sure they're all in the right place. I've had speaker wires smoke for some odd reason previously (probably a dodgy PC speaker).

A friend of mine has a similar problem, but I think it's just the motherboard that keeps being killed, he's just had his second motherboard die. Could be PSU related. (but the other way round compared to your problem!)

You could try building the PC barebones (PSU, mobo, cpu, ram, hd etc) out of the case to rule out the case causing a problem. Then try adding extra components one by one to see if it's a specific part.

My suspicion is that you may be overloading the PSU on one of the rails, eg it's 400w, but will only provide 80% of that max ~320w and that's split further still between the rails, eg +12v rail will have 20% of that, +5v 70%, etc so if you've got too much draw on one of the rails then it might go kerput. (figures are just examples and guestimates... but it should give you some of these figures on the actual PSU).

joshwa,

Thanks for the suggestions!

What I think I need to do is take the motherboard out of the case and run it on the bench, to minimise any likelihood of the problem being due to the case or the fitting of the motherboard to the case but, sadly, even doing that still means there's a risk of another PSU being killed.

Any more suggestions for the Save-the-PSU pot?

I've known this to happen in areas with very poor mains electricity quality... some friends of mine moved to deepest darkest rural France and got through 2 PSUs in a week. The first time they had no surge protector, and the second time they did and it still blew. They've now got a UPS unit and all seems to be working fine.

I doubt this applies to you though...

Fraz,

You swine! How did you know I didn't speak good French?

And how dare you tell the world!

;-)

Further comments greatly appreciated!