Sign in with
Sign up | Sign in
Your question

4 pin cpu power socket causes pc to not boot

Last response: in Motherboards
Share
July 12, 2008 4:44:36 AM

Hey guys. My pc had shut down a few days ago and I narrowed down the problem today. Everytime I plug in the 4-pin power socket on the motherboard for the cpu, the pc does not boot at all (no fans running etc). When I unplug the cpu 4-pin on the motherboard, everything is fine. The fans run at their at their normal speed (led and gpu). Obviously, there is no post since the cpu is unplugged. Did my cpu 4-pin power socket short circuit? I tried putting an old cpu in (athlon 3000+) but the same problem occurs. Thanks for any help!

My specs are :
Amd Opteron 180
MSI K8N Neo4 platinum motherboard
2gb gskill ddr-400
ati 3870
July 25, 2008 10:51:48 PM

I'm having the same issue, and would like any help available, if anyone out there knows what is the issue here. I attempted to install a second HDD, and when I press the power button the PC would flash on only to turn off for 3 to 4 seconds, and attempt to boot, repeating until I pull the plug. Pulling the 4-pin cpu power cord also fixes it (minus boot obviously) so it seems something is unsat...
July 26, 2008 9:48:02 PM

Just want to throw this out there since no one else mentioned it, I ended up fixing my infinite boot cycle by using the "jumper" pins for the CMOS to reset it. I didn't know of this until some more research after the post above. Somewhere on your board should be a couple pins labeled something to do with "CMOS". Grab a screwdriver (flathead worked nicely for me) and touch the two pins at the same time, effectively shorting out the CMOS and forcing the BIOS to do a reset, it seemed anyway. Afterwards I booted and was given a screen of choices, I went with last known working, and up came BIOS.
Related resources
July 28, 2010 2:53:16 AM

Hi guys. Sorry for the thread resurrection, I've been a week without a computer and I really really wanna get this solved.

I have a similar problem. I have gone through 3 PSUs and decided they are not to blame. Furthermore, I've two working PCI-E cards so I don't think the problem lies there either. Here's the history of what happened...

Day 1. Power button caused the fans to spin for 1 second then die. Incidentally, I took it to a location that was MUCH colder, and after blowing out some air (it wasn't bad, I already did it a week ago) I got it working, nothing was changed. So I took it home and same thing, fans spin for 1 sec and die.

Day 2. Took it back to the cold basement, figured the PSU was to blame (it wasn't sending proper voltage down the rail) so I replaced it with a lower wattage one. It worked fine in the basement. Took it home, booted up once, then had the system reboot. Now when I press power fans spin for 5 seconds and stop, then restart. I also have NO display. I figured GPU might be bad or drawing too much power so I replaced it with a much much weaker one, and still same thing. NO DISPLAY, FANS SPIN 5 SECONDS THEN STOP, REBOOT.

Day 3. Figured the PSU must be bad again. Bought an OCZ 600W (had 550 and 480 before) and still...fans spin for maybe 8 seconds now and then stop, reboot. But again, NO DISPLAY.

Throughout all this: I hear NO POST. I have an ASUS P5Q3 Deluxe Wi-Fi, I believe it has an onboard buzzer (no pinout for computer speakers) so I should be hearing a POST. But no.

So...is it the heat...the mobo...or the cpu? Tomorrow I'm taking apart the CPU, making sure there's nothing breaking contact, and putting it back together. Not gonna use more thermal paste for now.

If that doesn't solve the problem...do I RMA the mobo? What if I get it working again in a cold basement...what does it mean for a computer not to want to boot when it's hot?

Thanks so much, again, sorry for the revival.
August 25, 2010 10:13:22 AM

Had the same problem myself, changed mobo, cpu, psu, still wouldn't turn on when cpu 4 pin power connector was mounted.

Took out mobo, and made sure bottom was insulated and in no way connecting to metal, and tried again, same result.

BUT: now that the mobo was out, i could see that I had had the 4 pin connector plugged in at a 90 degrees angle to what it should have been.

Turned it to correct angle, and mobo will spin up.
But I am afraid I have just killed two cpu's :( 
August 26, 2010 8:10:29 AM

hello guys i have the same problem

if i unplug the 4-pin cpu power, all cpu fan and led are working fine but when i mounted it again it doesnt show any reponse when i press the power button..

if anyone have a solution for this problem.. pls tell me i really need it..

btw.. i already tried changing the PSU,CPU and video card still nothing happen..


thnx
jp26198926
Anonymous
a b V Motherboard
a b à CPUs
August 26, 2010 7:07:05 PM

Unbelievable. I just received a pc that I literally cleaned approx. 2mm dust from the cpu. the fans spin for 1 second - if that - when everything is connected, but when i remove the 4-pin, it powers the rest of the components just fine. did anyone solve their problem yet?
August 26, 2010 8:30:12 PM

Hi Everyone.

I got a new PSU and that did not solve the problem :( 

I RMAd the motherboard and that did not solve the problem :( 

Only after getting a new CPU did the problem get solved... :) 

Now, it could be that the CPU was fine but it was getting hot due to worn out thermal paste or HS or fan. Hence why it worked sometimes in a cold basement.

if you have this problem I'd suggest a new CPU.
August 27, 2010 7:22:53 AM

rykoshet said:
Hi Everyone.

I got a new PSU and that did not solve the problem :( 

I RMAd the motherboard and that did not solve the problem :( 

Only after getting a new CPU did the problem get solved... :) 

Now, it could be that the CPU was fine but it was getting hot due to worn out thermal paste or HS or fan. Hence why it worked sometimes in a cold basement.

if you have this problem I'd suggest a new CPU.



i already tried other cpu sir.. but did not solve my problem..
maybe this is a possible cause of mainboard problem/shortage..
a c 156 V Motherboard
a c 172 à CPUs
August 27, 2010 9:15:49 AM

Sigh. Time for some adult leadership. :) 

If you check the stats for this post, there were almost 1400 "looks" and no real answers. The regulars are avoiding this thread. Most of you violated a couple of forum rules: please don't resurrect dead threads and "one problem per post.

But OK. You all have the same problem. Your systems seem to work without the CPU power plug installed, but die when you plug it in. Right?

What is happening is that the PSU is able to produce enough power to run fans and turn on LED's without the CPU power plug. Nothing else is working. And the illuminated motherboard LED means very little. All it means is that the PSU is plugged into a live wall socket and the PSU is switched on.

Most, but not all, of these problems are caused by using really cheap PSU's that are failing under load.


Work through our standard checklist and troubleshooting thread.
http://www.tomshardware.com/forum/261145-31-read-postin...
I mean work through, not just read over it.

Breadboard - that will eliminate any kind of case problem you might have.
http://www.tomshardware.com/forum/262730-31-breadboardi...

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:
http://www.cwc-group.com/casp.html

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. 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.
http://www.youtube.com/watch?v=5FWXgQSokF4&feature=yout...

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.

If, after working through this, you still need help, you will be better off posting in the Homebuilt Forum.

Good luck.
!