new motherboard fan still starts for a second

[lizzieborden]

Hi all -

About a month ago the screen on my computer went black. I rebooted and no hdd's could be detected. Wanted to reflash bios to see if that helped but when I restarted the pc the power supply died (I had it tested). Replaced the power supply and booted the computer. It started up once and then never again. The fan came on for a second then dies. So I purchased a new motherboard and put the old cpu in the new motherboard (Asus P4S8X-MX). Same thing fan comes on for a second then dies. Took the ps to a computer place and had it tested. It's fine. So I bought a new cpu and put it in the new motherboard. Same thing... fan comes on for a second then dies... Please help???? Very frustrating.

 

[electronicsfreak]

I think your new moterhbaord and old one probally got grounded to the case. I think the motherboard is bad again. Might want to be sure there not grounding to the case. Also wear an anti static bracelet or hold one hand on case to avoid static shocks. I learned that lesson the hard way lol.

 

[franklin97355]

Take the whole computer to the computer place and let them find the problem. It's hard to find a problem when you only give them one part at a time.

 

[lizzieborden]

I took the old board, the old cpu and the new ps put it on a static bag shorted out the power and low and behold it works. What now? I don't know anything about grounding the case??

 

[lizzieborden]

Sorry franklin97355. I'm a 15 year network admin and certified tech. My ego won't let me pay to have someone fix my equiptment. I'd rather rely on tek-tips.

 

[electronicsfreak]

Ok what I meant by grounding to the case is this. When putting a motherboard in sometimes part of the board makes a connection to the case and shorts it out hence the term grounding to the case. This will cause a motherboard to either fry, not work right or a million on problems. Its easy to do for sometimes one little piece of a part has a lead just a millimeter long enough to touch the metal of the case. So be sure nothing is shorting out anywhere on the case. If it worked when it wasnt in the case then im 98 percent sure it was shorting out somewhere on the case. If you can use some plastic spacers that keep the board off the metal case.

 

[lizzieborden]

Thanks electonicsfreak. I'll try it later on and let you know how it works. Could I use rubber washers under the board instead?

 

[edfair]

The motherboard is intended to be grounded at several places. The mounting holes where grounding is intended have solder pads to make contact with brass standoffs. Those mounting holes that don't have solder pads are intended for nylon standoffs.
Screwheads on the screws connecting to the brass standoffs can be large enough to cover traces running nearby. So you use screws with heads large enough to hold the board but small enough that they don't short things.

The usual problem is extra brass standoffs, but not always. Floppy power connector off by one contact will cause the same problem. Best to get the M/B running with nothing else connected, then start adding things on.

Ed Fair
Give the wrong symptoms, get the wrong solutions.

 

[paparazi]

lizzieborden
The original and I'm guessing, cheap generic power supply, has likely spiked and permanently damaged either the hard drive, CDRom device or addon card, basically damaging circuitry and causing one or more to short to ground.
As a result when you connect you new PSU you just get a split second of power and nothing else.

I'm suprised others didn't imediately point to this common result of a PSU burn out.

Try to see if it will post without hard drives, CDroms or any addon cards connected, just new PSU, graphics if seperate, CPU with fan and one stick of ram.

Sometimes you can even see a burn "pit mark" on the hard drives PCB chipset.
Martin


We like members to GIVE and not just TAKE.
Participate and help others.

 

[lizzieborden]

Paparazi -

The original power supply was definitely not cheap. The replacement is though... Why would the psu, and fan work out of the case? I even get beeps out of the case but not in the case. Same scenerio, nothing attached but the psu, mobo, tried it with and without the cpu?????

 

[paparazi]

So you are saying the system boots when all components are connected outside the case?
So you have connected HDD's, CDroms etc etc outside and it goes to windows?

My guess it the you have one to many mounting posts, these brass standoff's should only be fitted in the places that align to the brite solder rings on the motherboard, nowhere else.

Are you also using the extra power connectors on the motherboard 12V, just check.

Martin

We like members to GIVE and not just TAKE.
Participate and help others.

 

[edfair]

I've run across one where the I/O plate grounding strap for the top of the USB ports was bent down enough that it went into the USB connector.
Grounding problems, as you are apparently having, can take some effort to locate. It can be extra standoffs, but you should be able to tell from the top of the board, too. The top should have solder rings where screws should go. And make sure you have the same number of screws as standoffs.
There are also cases that have embossed mounting points instead of standoffs. These are particularly prone to creating problems as the embossed structure is larger in diameter than the brass posts.

Ed Fair
Give the wrong symptoms, get the wrong solutions.

 

[paparazi]

Yes indeed edfair, but to make this mistake over and over when it's so obvious to see? hmmmmmmmmmmmmmmmmmmmmmmmmmmmmm
Maybe lol.
I've also seen case's where there have been one or more permanently riveted posts IN THE WRONG PLACE, I've had to resort to brital means of removal!
Martin


We like members to GIVE and not just TAKE.
Participate and help others.

 

[edfair]

Moto tools are not brutal!!! Noisy and messy, though. :<)
Besides, two thicknesses of electrical tape will cover a multitude of extra standoffs.

I think we are pretty well agreed that something is grounding out.

 

[paparazi]

I must say I see lots of people posting that they use these fibre washers to insulate the mounting posts, WHY?

In all my years I've never had a problem with shorting, as long as you are careful to center the posts to the mounting holes and the correct screws are used (not ones with a wide shoulders)
Also it is vital that the builder is carefull not to allow any earthing "fingers" on the I/O plate to bend the wrong way and protrude into USB/or Ethernet ports.

Occationally I've seen problems with "short" early ATX cases that are not very deep (front to back) on these cases there is often a problem with CDroms catching the motherboard in some way.

Sticky spondge pads are very useful for insulating in such instances.

Martin




We like members to GIVE and not just TAKE.
Participate and help others.

 

[edfair]

Don't recall using one for probably 5 years but I still have my collection, along with the pieces of paperclip that hold them in place while the M/B is lowered in place.
I fought too many battles trying to get boards exactly positioned to prevent grounding with some of the cheaper motherboards and cases. It seems in the worst case that all the board tolerances were one way and the case tolerances were the other.
It may be that the ATX specs are tighter, ot that the case manufacturers are being more careful. But I can remember the earlier days of drillbits and moto tools to get things to fit together.

Ed Fair
Give the wrong symptoms, get the wrong solutions.