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-   -   Power Supply failure or Motherboard failure? (

neilthereildeil 06-04-2008 12:33 AM

Power Supply failure or Motherboard failure?
hello. there was a very large thunderstorm very close to my house a few days ago, and a lot of electronics in my house stopped working. among them was my linux desktop, even though it was behind a surge protector :( when i hit the power button, i see the power LED on my case light up and SOME of the fans inside my case start spinning. I dont see anything on the screen, and i dont hear any beeps from the computer's internal speaker. after about 20 seconds, the whole computer shuts off and nothing else happens. do you think this is a PSU problem(maybe the computer isnt getting enough voltage, so it partially starts(LEDs light up etc, but the full computer cannot boot, so it shuts off) or do you think its a motherboard problem or do you think this is a problem with sm other hardware? FYI, my PSU is from Enermax, and my Motherboard is Asus P5b-e. thanks in advance.

pinniped 06-04-2008 12:59 AM

Ouch. Near strikes are fatal to electronics. A surge protector is only useful if it is properly earthed (and properly designed). I had a Belkin model go up in smoke but the attached stuff was still working (more luck than anything; typically a fried suppressor = fried computer etc). Anyway, rather than take chances, another Belkin went in. :) Better $300 lost than $6000.

There is a pretty good chance that the PSU blew some components and protected the MoBo; the only way to test is to open the case and check the voltages at the test points when the PSU is initially powered up. If you don't know what I'm talking about, the best thing to do is get a replacement PSU. If the MoBo still won't boot or at least beep, then it's screwed (and if the MoBo's screwed, the old PSU is guaranteed to be screwed).

neilthereildeil 06-04-2008 07:27 PM

which contact points would i check the PSU voltages at? I dont think ill see a high voltage because the PSU wont be under any load. we only see a high voltage when the PSU is under high load, right. the PSU doesnt CONTINUALLY draw 550 Watts. i think when they saw 550 Watts, they mean peak power output. also, how would i test the motherboard to make sure it still works?

pinniped 06-09-2008 04:47 PM

For a start, you can check the +12,+5v on those 4-pin power connectors (the ones for the HD etc). For other test points you need to look at the MoBo itself; if you're lucky the manual will even tell you a bit about the test points.

Since you mention that the fans turn on then off again, that suggests that the power supply is switching off because the minimum load current is not being sensed on the 5v line. A 15W 1ohm resistor from 0v to the 5v terminal on the power connectors should be enough to ensure that the power supply stays on, provided the 5v portion of the supply is actually working.

Just to complicate things, not all power supplies are the same and some may have a section which is devoted to providing power to the CPU; in such a case, if you can't locate the test points, you need to test voltages by poking a probe into the back of the main power connectors. For an AT type power supply, you can search the internet for the pin numbers and what voltages to expect on each. (Some are control and signal lines though, not voltage sources.)

By the way, you have to have pretty good hands and handle a voltmeter well before playing with a computer and it's power supply; one slip can produce some impressive sparks and smoke. Sometimes you need a special probe to get into some places.

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