Tech-heads hardware problem in 'ere

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Couple of weeks ago I built a media pc for the living room, it worked fine for a couple of days then just died while watching a tv program on it.

Symptoms, the psu and fans all fire up as soon as mains is switched on, i.e. no need to press power button, but the mother board won't post, no sign of life there at all.

Sent the mobo (asrock matx type) back after much faffing about getting Stak to action the RMA. Yesterday after chasing it up the engineer called back and said yup faulty, we've boot tested a replacement and it's on it's way.

The replacement arrived today, with exactly the same problem as the previous faulty one (it is a different mobo) as soon as I apply power the fans start, but no sign of life from the mobo.

I've checked all the voltages coming out of the psu, even tried a different one with no joy.

Any ideas if something other than the mobo can be causing it? I'll be calling Stak again in the morning to see about returning this one but I want to be sure it's definately the mobo at fault and not another component causing it.
That all said I've stripped the mobo down to cpu only and there's no difference.
 
If you've a working (as you say checked) PSU and it doesnt get as far as the BIOS then its almost certainly 1 of 3 things. The MOBO, the CPU, or an expansion card. Most systems wont come out of reset unless the CPU is live, they need this to start. Then the bios kicks in which does the memory test. If its onboard graphics and you have no expansion card plugged in then you are back to the CPU or MOBO.
 
I'd get post error beeps if the processor was faulty though wouldn't I?
 
Dunno if this is remotely relevant, but I once had a problem where the PC would appear to start booting then shut down again within 10 - 15 seconds.

It turned out that the CPU fan speed sensor wasn't returning anything, and the BIOS was set to shutdown on CPU Fan failure.

I think I reset the BIOS to factory settings (which was to not shut down on failure) and replaced the fan when I knew what the problem was.
 
try disconecting the power switch, and either change the wires from the reset swith to power the pc, or if you are confident just touch the power connectors on the motherboard with something like a screwdriver to see if it boots, (be carefull that you do not short anything else though)
I once had a newly built system that had all sorts of weird errors, changed everything including the cpu and motherboard, after a couple of weeks pulling my hair out, eventually traced it to a faulty power switch on the case, changed the connectors to use the reset switch as a power switch, then everything worked ok.

alwyn
 
I had the same problem's a while back , while i was getting the correct voltage from the psu was not able to provide sufficient wattage, thus created a thermal problem to KO two mother boards before it corrected in time.
 
On the basis that the system will not come on and that the power supply fans should not start until you turn the system on i'm going to say rather confidently that its your psu (and don't want to sound big headed but just backing myself up by letting you know i've been building / repairing pc's for over 11 years)

Hope this helps
 
Thanks sgotwr, this one powers up with the switch disconnected so not that I think. Ryan I've got a 600w psu in my main pc I'll give it a shot tomorrow, can't see why a lack of power would display these symptoms though.
 
harrison1980 said:
On the basis that the system will not come on and that the power supply fans should not start until you turn the system on i'm going to say rather confidently that its your psu (and don't want to sound big headed but just backing myself up by letting you know i've been building / repairing pc's for over 11 years)

Hope this helps
Click to expand...

ok m8, as I said above I've got another one so I'll give it a shot tomorrow.
 
When you test it with your other PSU, do not plug anything else in at all, including HD, CDRom.
Hard disks can cause symptoms like you describe, (favourite I found was plugging in CDRom IDE upside down, no beeps, no post).
I assume that this is an ATX power supply, how did you get it to turn on without the motherboard? If you used the wrong size resistor you could damage the PSU (ATX should only present 5V unless they are turned on by a resistance on two pins).
You do not state what type of processor. Many of the newer Intels require an extra 6/4 pins of 12V connected, this often causes the same symptoms if these are not connected (this can be in addition to, or instead of the 20/24 pin connector). (hmm, possibly not the problem if it worked for 2 days).
Similar problems can be caused if the low/dma area of the memory chip is corrupt. If you have two memory chips, swap their positions.
 
coldpenguin, it powers up when you switch on the mains wether or not the case power switch is connected.

I'm fairly sure now that Harrison and Ryan are right. I just tried the psu in my main pc and it will power up but that's it, it won't boot. Seems I may have two faulty power supplies here :( Good news is the new one came from PCWorld so I can at least take it back and get them to check it.
 
Still strange that fans start without the switch being used though?
 
hhmmm got the power supply exchanged, plugged in the new one and same problem exactly :(
 
Check on the mobo for a jumper that's used to reset cmos. If the jumper is set, the system will not boot. The only apparent operation is the fans. If you have one unset the jumper and try again. Some mobo's ship with it set, got no idea why as it makes it seem like the mobo is DOA
 
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