tooth

Help me to troubleshoot a friend's homebrew system. It is not powering up. No fans, no beep, no HD spin up, nothing. The only sign of life is an LED on the mobo. So how can I tell if the culprit is the power supply or mobo? My suspicion is the power supply, even with a bad mobo, I could at least expect the fans to run. Right? It has been too long since I have worked on computers at the component level, so my troubleshooting skills are a little rusty.

Jinn

Check the PS in another computer if you want to be sure, but I can say almost certainly that its not the PS. If it were, you probably wouldn't be getting the power LED on the motherboard.

I had this same problem last christmas.. new motherboard, new CPU, new RAM.. new case. Plugged it all together.. and..........NOTHING. Turns out the CPU wasn't seated correctly and I had too much Arctic Silver on the heatsink. You'd be getting beeps if the RAM wasn't right or a peripheral wasn't seated, so I'm betting on CPU. Check it out in another MB if you have one laying around with the same socket configuration...

As for the fans.. on new motherboards, you actually need a signal from the motherboard to fully spin up the PS, including powering the fans.

Another thing to try.. check the power pins on the motherboard, you might have the power switch hooked up backwards or on the wrong pins.. try jumping across the poles with a screwdriver and you might get it to fire up.

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"I'm typing on a computer of science, which is being sent by science wires to a little science server where you can access it. I'm not typing on a computer of philosophy or religion or whatever other thing you think can be used to understand the universe because they're a poor substitute in the role of understanding the universe which exists independent from ourselves." - Willravel

Cuatela

If you have no power except a small amount to the motherboard, then it's probably the power supply. I'd recommend borrowing an equivalent power supply that you know works to test it. If the other one does the same thing, then it's the motherboard.

Also, you could google "diagnostic cards". We've got one at the office that you plug in, and it gives a code for the problem it encounters. If it's the power supply, it won't work at all, but if it's the motherboard or something else, it'll tell you.

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Any sarcasm was intentional.

sashime76

MB isn't getting any juice for sure. Do you see one or two connectors on from the power supply to the MB? The 20 pin is the obvious one, there may be a 4 pin that also needs to go on the MB. Connect only PW connector from the front panel to MB, don't hook up Reset, HD LED, etc. Use the manual!!

tooth

I know swapping out known-good parts is the best and simplest way to narrow down the culprit. The problem is, I don't have spare parts. Everything I have at work is Dell, and last I heard, they use a non-standard power supply pin-out. So unless that has changed in the past couple of years, I'm SOL there. Can anyone confirm or deny that?

- Last night, I double and triple checked the power switch on the case. Even checked it with a meter, to be sure that the switch itself actually closed when pressed.

- I only did a visual inspection of the CPU, it looked like it was flush to the socket. I didn't want to muck around with taking it out and putting it back in. I couldn't readily see how to take the heatsink off, and didn't want to force something and risk cracking the damn thing, so I let that be for now.

- I have disconnected almost everything from the motherboeard, to be sure that some rougue component wasn't pulling down the supply. Only thing left connected is CPU, RAM, and video card. I'm thinking, I could even take RAM and video out, and at least something would happen, if all else was OK. And I'm thinking that even with a dead CPU, the fans would at least spin. Right or wrong there?



So what I'm down to is, short of swapping parts, is there anything left for me to do?

wayne21

I just hard the same problem and the led on the mobo was on with nothing coming on!
I went and bought a new power supply connected it led light on and nothing else no fans nothing.
Let me say also I was a little rusty as well.
returned the power supply had them test it / it was bad!!!
bought a other one after they tested it, installed it led light and nothing else???
I broke down and took it to a friend with a shop tested the power supply again it was okay, after a little more minor testing he told me it was the mobo!!!
Got another on just like what was in it installed it and I'm up and running.
The power supply trick me because I thought the fans would run if it was good, but the mobo has to signal them/ be under a load to run.
I would try to find a way to test the power supply(even if you have to take to someone first, then mobo!!!!)
WAYNE 21
Hope this helps.

wayne21

the fans will not run if the mobo is bad and the power supply is good.
even with the bad mobo I got the led light on the mobo and it was bad!!!!!

wombatman

When you say the fans run, does this include any case fans? Also, do any fans connected to 3-pins on the motherboard run? If so, then it's not the power supply. You may wish to try switching out the motherboard if this is the case.

tooth

No, the fans do not run.

wombatman

Then I would think power supply.

Jinn

lol I give up..

Also:

Wrong.. the power supply converts AC to DC and gives the desired wattage.. the MB controls peripherals, on/off, and fans.

__________________
"I'm typing on a computer of science, which is being sent by science wires to a little science server where you can access it. I'm not typing on a computer of philosophy or religion or whatever other thing you think can be used to understand the universe because they're a poor substitute in the role of understanding the universe which exists independent from ourselves." - Willravel

tooth

Don't give up on me!

I know that the mobo "reports back" to the power supply to keep it running. I'm just saying that I thought that it (the mobo) would still do that even without a working CPU, or even RAM. Wouldn't the system stay on, but beep error conditions? Just trying to rule out possible causes.

flat5

I'm not sure, but I think:

you can test the PS by shorting two pins on the PS connector that goes to the motherboard. This should start the PS fan. Sorry, I don't know which two pins on the PS connector you short. Maybe Google for more info.

Then I guess you could check with a meter other pins on the connector for voltage relative to one of the ground pins.

This bypasses the logic function on the MB that would switch these two pins.

Jinn

Do you have another tower anywhere in your house? Four screws later, you could have it plugged it into your motherboard. Still not working? Well then you've likely removed one suspect.

As far as I know, no. Without a Central Processing Unit, the motherboard does just about.. nothing. No beep codes, no fan initialization. The reason I am so curious about the CPU/motherboard in this situation is that I had a very similar problem:

Christmas '04 I got a new motherboard, CPU, case, and RAM. I carefully put the motherboard into the case, covered the CPU in artic silver thermal paste, attached the heat sink, attached the 6 case fans, plugged in the video card and hard drive, put the RAM in -- and hit the power button. Click........ click... click.. all I heard was me clicking the power button over and over hoping for something. Days later, after having tried another power supply, disconnecting the peripherals, checking the RAM.. jumping the power terminals with a screwdriver.... it still didn't work. I pulled the CPU out, cleaned off some of the thermal paste (I put on WAY too much)... carefully reseated it and reattached the heat sink -- and voila... it fired right up.

Also: try searching google for the CPU, motherboard, and CPU and motherboard. There might be a known incompatability, or someone might've had a similar problem.

__________________
"I'm typing on a computer of science, which is being sent by science wires to a little science server where you can access it. I'm not typing on a computer of philosophy or religion or whatever other thing you think can be used to understand the universe because they're a poor substitute in the role of understanding the universe which exists independent from ourselves." - Willravel

Hardknock

Homebrews don't die. They mutiply!!!!

Keep working man. It'll be worth it to get it up and running again. You have lots of good suggestions.

Together we can all send Michael Dell back to college cause he had to get another job.

Gatorade Frost

I'm gonna say BS - I built a computer this summer and the motherboard came in dead - But all the fans worked, and the PSU was good.

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I got in a fight one time with a really big guy, and he said, "I'm going to mop the floor with your face." I said, "You'll be sorry." He said, "Oh, yeah? Why?" I said, "Well, you won't be able to get into the corners very well."
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