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Home-built Computer Not Working

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Simon

Mon Aug 28 2006, 05:27AM

Registered Member #32 Joined: Sat Feb 04 2006, 08:58AM
Location: Australia
Posts: 549

This isn't too much of a surprise but I need to diagnose the problem.

My parents wanted a better computer so I ordered the parts, they arrived, I spent several hours putting them together and when I turned on the power it didn't work.

The power switch has no effect. The power supply does seem to work - I unplugged it and shorted the green power-on wire to gnd and that turned it on (I didn't check the voltages).

It's a 400W PSU but in case that wasn't enough I unplugged everything that wasn't necessary so now there is just a PSU, a CPU (2.6GHz Celeron) and some RAM (512MB DDR) on a motherboard. It still doesn't work but I noticed that when I applied any mains power there is a quiet, rhythmic clicking noise that speeds up as it dies away when the mains power is disconnected. That reminds me of the buzzing other PSUs I've had make when shorted. I'm not 100% sure the sound comes from PSU since I have to stick my head in the case to hear anything.

To me it looks like a dead motherboard but I know a lot of users here have more experience with this than me so I thought I'd ask for opinions.

Any help would be greatly appreciated.

Bjørn

Mon Aug 28 2006, 06:23AM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

To test the PSU you need to put a load on the 12V line and maybe on the 5V line to make it regulate properly. 5-20W, something like that. I have had the clicking a few times when the load has been too low. Usually when there is a short the PSU shuts down permanently until it is turned off and on again.

The quality of computer parts have been declining rapidly the last few years.

Avalanche

Mon Aug 28 2006, 11:14AM

Registered Member #103 Joined: Thu Feb 09 2006, 08:16PM
Location: Derby, UK
Posts: 845

This might sound stupid but are you sure the case switch is connected to the correct header on the mainboard? That's the first obvious thing, secondly I would check for a faulty switch. A few weeks ago one of my old systems refused to power on, and it was just the cheapo switch failing to work. Try shorting the switch header with a jumper.

...

Mon Aug 28 2006, 01:25PM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

The clicking sound does sound like a shorted mobo (like you probably dropped a screw under it or something) try shorting the power wire while it is connected to the mobo and see if it works. Triple check that the switch is in the right place and that it works. If that doesn't work completely strip the mobo of everything but put a voltmeter on the 12v line and power it up (with the case switch first then jumping the wires) and see if you get 12v. If still nothing then pull off the mobo to check for shorts.

The 400w psu is plenty, I have a p4 2.5ghz, gforce4, and 4 hard drives (a 40gb 7200 barracuda, a 100gb caviar, and 2 200gb 7200rpm barracudas) running off a 250w psu

Do you have another psu and mobo you could try... I know that not everyone has spare computers laying around but it would be helpful if you did

Electroholic

Mon Aug 28 2006, 04:56PM

Registered Member #191 Joined: Fri Feb 17 2006, 02:01AM
Location: Esbjerg Denmark
Posts: 720

first thing to check would be power to mobo.
teh 20pin atx or 24pin Eatx power.

AND i notice no one said anything about
teh 4pin Aux 12V power(since P4/about 3 years ago)

there might even be male molax on the mobo/graphix

if you are sure everythign is pluged in right, adn its still not working. rip everything out gently.

because some time if you screw the mobo too tight onto the case, you can short it.

so try build teh system on an insulated surface.

adn dont use a jumper to short the power sw pins,
instead, touch/short them with a screw driver.

edit:

oh and the clicking sound is normal,
lots of psu does that when power is removed.

Simon

Wed Aug 30 2006, 04:38AM

Registered Member #32 Joined: Sat Feb 04 2006, 08:58AM
Location: Australia
Posts: 549

BjÃ¸rn BÃ¦verfjord wrote ...

I have had the clicking a few times when the load has been too low. Usually when there is a short the PSU shuts down permanently until it is turned off and on again.

The quality of computer parts have been declining rapidly the last few years.

The clicking occurs when the PSU is simply plugged into live mains, connected to the mb. It's as if the 5V standby line is being shorted or something, if it is a problem. I'll try adding a load to the test. Thinking about it, that's a good idea.

As to the switch, that was my first thought. I checked the connections but I don't know why I didn't think of manually shorting it. I guess I'd been working a long time and was sick of it.

I was also careful about keeping screws off the board but I'll double check.

More later.

Steve Conner

Wed Aug 30 2006, 10:17AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

My work computer died one day with the same problem. The PSU just sat clicking endlessly and the power switch did nothing. Turned out to be a dead motherboard.

Nik

Wed Aug 30 2006, 06:13PM

Registered Member #53 Joined: Thu Feb 09 2006, 04:31AM
Location: Ontario, Canada
Posts: 638

Does any one here know why a PSU clicks when it's shorted out?

Marko

Wed Aug 30 2006, 08:11PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

It probably turns on andd off as the overcurrent circuit trips. Main HF transformer makes a click when it is started.

Buck converter on motherboard usually dies with mosfets shorted causing the SMPS to do this ^

I used to run many ATX SMPS's without any dummy load and they always worked fine 'on air', no regulation problems or anything..

Steve Conner

Wed Aug 30 2006, 10:26PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Like Firkragg says (and he's probably right, those MOSFETs lead a hard life cranking out ~70A with no heatsinks) it's the overcurrent protection. The PS tries to fire up, and if it detects overcurrent, it aborts and then tries to start again after about a second. And so on. The SMPS weenie technical term for it is "Hiccup mode". Not all SMPS do it, some just limit their output current like old-fashioned linear PSs, and sometimes when you hit this limit the PS makes a nasty squawking or frying sound. I once modified a SMPS to have a "proper" constant current output without any comedy sound effects, for charging batteries.

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