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System wont turn on. PSU issue?

Last response: in Systems
October 31, 2010 9:35:45 AM


I have just rebuilt my PC.

Gigabyte ga-890fxa-ud5
phenon 1090T 6 core
4gb of RAM
windows 7
ati 5850 1gb gddr5
Coolermaster Hyper TX Cpu cooler

I did have a 600 watt PSU running my old rig, but showed signs of failing (graphic glitches) due to the lack off leads (it installed Windows 7 fine) and the new GPU. So I bought a Antec 750W truepower ATX, on Saturday (yesterday), to run it. Updated windows, installed antivirus and was running smoothly (installing Fallout 3 ) when suddenly the computer turn off (like a power cut). When I pressed the power button nothing happened.

So i took my case off and unplugged the power cord, waited and hooked it back up. The mobo lights come on but when I hit the power button nothing happens, except the GPU fans and internal fans spin once.

I took it the whole system apart, checked for an signs of short circuiting. Tried again, it fired up heard the successful system boot 'beep' and the computer powered down again and the same thing is happening. Mobo lights on, fans spin for a sec (after I remove/replace the power cord).

I left it for a few hours and tried again. I tried with the holding the power button down, it booted and switched off as it should. I pressed it again, started to boot, heard the single short 'beep' and then it powered down again like before. LED on mobo stayed on as usual. Tried again and then same thing happens, fans spin once and then stop.

I took this a good and bad sign. The good was the boot 'beep' suggesting my mobo and components are not fried, the bad my PSU is dead...

Am i right?

a c 122 B Homebuilt system
October 31, 2010 10:54:40 AM


Work through our standard checklist and troubleshooting thread:
I mean work through, not just read over it. We spent a lot of time on this. It should find most of the problems.

If not, continue.

I have tested the following beeps patterns on Gigabyte, eVGA, and ECS motherboards. Other BIOS' may be different.

Breadboard - that will help isolate any kind of case problem you might have.

Breadboard with just motherboard, CPU & HSF, case speaker, and PSU. You do have a case speaker installed, right? If not, you really, really need one. If your case or motherboard didn't come with a system speaker, you can buy one here:

You can turn on the PC by momentarily shorting the two pins that the case power switch goes to. You should hear a series of long, single beeps indicating memory problems. Silence indicates a problem with (in most likely order) the PSU, motherboard, or CPU.

Remember, at this time, you do not have a graphics card installed so the load on your PSU will be reduced.

If no beeps:
At this point, you can sort of check the PSU. Try to borrow a known good PSU of around 550 - 600 watts. That will power just about any system with a single GPU. If you cannot do that, use a DMM to measure the voltages. Measure between the colored wires and either chassis ground or the black wires. Yellow wires should be 12 volts. Red wires: +5 volts, orange wires: +3.3 volts, blue wire : -12 volts, violet wire: 5 volts always on. Tolerances are +/- 5% except for the -12 volts which is +/- 10%.

The gray wire is really important. It should go from 0 to +5 volts when you turn the PSU on with the case switch. CPU needs this signal to boot.

You can turn on the PSU by completely disconnecting the PSU and using a paperclip or jumper wire to short the green wire to one of the neighboring black wires.

This checks the PSU under no load conditions, so it is not completely reliable. But if it can not pass this, it is dead. Then repeat the checks with the PSU plugged into the computer to put a load on the PSU.

If the system beeps:
If it looks like the PSU is good, install a memory stick. Boot. Beep pattern should change to one long and several short beeps indicating a missing graphics card. Silence or long single beeps indicate a problem with the memory.

Insert the video card and connect any necessary PCIe power connectors. Boot. At this point, the system should POST successfully (a single short beep). Notice that you do not need keyboard, mouse, monitor, or drives to successfully POST.

Now start connecting the rest of the devices starting with the monitor, then keyboard and mouse, then the rest of the devices, testing after each step. It's possible that you can pass the POST with a defective video card. The POST routines can only check the video interface. It cannot check the internal parts of the video card.
October 31, 2010 11:06:08 AM

I have been touble shooting.. I gave the breadboarding a go. using the power switch on the mobo

CPU and HSF only. beeps say no memory / power error (held power down to turn off)
CPU and HSF and 2GB ram stick.. Long beep and 3 short = no GPU (help power switch down to turn off)
CPU, HSF, RAM and GPU = Power fails, PS fan half spins. LED stay on MOBO. Power stops itself

I think is my GPU so I take it out.

CPU, HSF and RAM = PSU half spins and stops
CPU and HSF = PSU half spins and stops.

Can I take my CPU out. noticed some thermal paste on the mobo itself below the HSF. Will that trigger a power failure?
Related resources
October 31, 2010 11:12:48 AM

Okay, i leave it a few minutes, take out power cord reinsert-

CPU and HSF = continous beeps = no RAM (powered down with power switch)/ power error (think they were short beeps)
CPU, HSF and a stick of 2GB ram = 1 long beep, 2 short = no GPU (this time I let it run and it powered down again)
CPU, HSF and RAM= i try turning it on and the PSU fan half spins and stops.
October 31, 2010 12:00:14 PM

Okay, I didnt want to do the paper clip test on the PSU as the unit is only a day old and was worried id void my warranty.. but I took the plunge.

It powered on with a case fan... and just when I was thinking it must be either my GPU or CPU the PSU shut down... like it was doing in my case.

Cheers guys... this forum is great!
a c 103 B Homebuilt system
October 31, 2010 12:12:51 PM

It happens with units even from top manufacturers.