Burn marks on motherboard connector

[MrBumpy]

Last week, my system began crashing. I would use it for about 10-20 minutes, and then it the monitor would go blank, and the system would be unresponsive. I would have to shut it down using the power button. I opened my case and noticed that two capacitors on the motherboard were bulging and leaking electrolyte. I figured this was the cause of my problems. My processor was an Athlon XP 2000+ and the motherboard was an Iwill XP333.

This week, however, when disassembling the PC for parts, I noticed brown burn marks on three pins of the power supply's 20-pin motherboard connector. My power supply is a 350-watt Antec that I have had for about a year and a half. I did not notice the burn marks a few months ago when I last opened my PC, so I figure that they are more recent.

My question is this: is the motherboard or the power supply at fault for the burn marks? If the motherboard was at fault, would it still be safe to use the power supply, even though it has burn marks? I've actually tested out the power supply with another motherboard, and it has worked fine for several hours straight, so I'm inclined to place the blame on the motherboard (the faulty capacitors point a few fingers in that direction as well).

Thanks for any insight you guys can shed.

 

[jonnyGURU]

Let me guess....

The burn marks coresponded with red wires on the PSU?

 

[MrBumpy]

Yes, that is correct.

 

[cheesehead]

How peculiar.

My guess is that the burn marks are caused by too much current moving through the pins, making them heat up like the heating element in a toaster.

 

[MrBumpy]

Originally posted by: Cheesehead
My guess is that the burn marks are caused by too much current moving through the pins, making them heat up like the heating element in a toaster.

That's what I figured as well. I wonder if the power supply can be trusted in another system, though. If it's the motherboard's fault, would it matter? I don't know if burning pins causes intrinsic damage to the power supply or not. I'll try opening it up tonight and see if I can see any signs of damage. The only reason I didn't do that yet was I wanted to check if it's still under warranty before I break the seal. I think the warranty has worn off, though, since my current power supply was an RMA replacement for an older one that failed.

 

[jonnyGURU]

It's a board problem. Not the PSU.

Can the PSU be "trusted?" Well, you're going to need to clean those pins up big time. Otherwise, you're going to have added resistance that's just going to become a problem on another board.

 

[MrBumpy]

I guess I'll take out the power supply for now, until I can find a way to clean the connectors. Does anybody have any ideas on how to do this? I've heard of contact cleaner, but I would have no idea how to get it into those little contacts.

 

[Zepper]

Yes, the caps on the mobo were shorting momentarily thus causing the excess draw and potential for overheating on the +5 wires. That and the likelihood of cheap contacts in the ATX connector from the PSU that can't really stand the current for which the real Amp or Molex contacts are rated. We see that quite often on mobos that power the CPU off the 5V rail.

There are lots of pix around of burned ATX connectors if you want to know that you aren't alone... There were some links to some really nasty ones on the forum here a while back. You can see some at the badcaps.com forums too.

.bh.

 

[GalvanizedYankee]

Badcaps.NET http://www.badcaps.net/

 

[Mark R]

Clean the pins on the 20 pin Molex connector up, and you'll be fine.

The burning connector is due to a design 'feature', arguably a design flaw, on the XP333. Essentially, it powers the CPU from the 5V supply from the PSU - this is fine for low power CPUs, but impractical for modern CPUs because the power demand is too high. For things like an XP 2000+ it's borderline, and not really a good idea.

Using a modern Mobo which powers most of its heavy loads from 12V should be fine, because the demands on the 5V lines are only relatively modest. However, it's essential to clean up the connectors, because the damaged connectors may overheat even under low-load connectors.

 

[Farmer]

Originally posted by: Cheesehead
How peculiar.

My guess is that the burn marks are caused by too much current moving through the pins, making them heat up like the heating element in a toaster.

That has to be it, though it'd take quite some current for a low-resistance copper wire to experience that type of heating (P=IR).

The only real way to know is to check potential difference against PSU for those suspect PSU rails (i.e., the 12V might be overvolting), but that only works when you power you mobo up... not too smart a thing to do.

EDIT: I see MarkR has the particular solution. Get a new board.

 

[lenjack]

If the contact between the psu connectors and the board connectors is not tight, say almost intermittent, this could cause arcing, which can burn the pins. Probably not what happened in your case

 

[Zepper]

Yup, you do have to have a considerable amount of current there, but more important is just the right amount of contact resistance to complement the current. It can get right toasty then... It's a cascade type of thing, first one pin's resistance goes high and the current tries to shift to the remaining low resistance 5V wires, then another can't take it and gives up, putting even higher stress on the remaining 5V contacts until soon enough, all the 5V lines to the CPU are involved. I've seen one pic with actual flames...

.bh.

 

[Jhhnn]

Using a straight pin or similar, the affected pins can be extracted out the back of the plug to facilitate cleaning, also squeezed down to the right diameter for reuse...

If the psu works, it works, but it'd be smart to check it internally for bad caps, too... the problem is endemic to all kinds of computer parts of that era- bad electrolyte recipe...

 

[FDCPCZ]

I had quite a lot of burnt out ATX connectors when i ran a farm of Athlons for DC projects.
Problem is CPU Voltage regulators being fed from the 5v lines.

You might be able to reuse the PSU again depending how badly burnt the ATX connector is.
What i did was to move the PSU's to machines using the 4 PIN connector for CPU power.
The 5V wires wouldn't get much load then.

If the ATX connector is extra crispy then you'd be best off binning the PSU.

 

[Pez D Spencer]

Why risk another machine with an old 350W PSU? Do like FDCPCZ says and toss it in the bin.

I went over to that badcaps.net site that someone mentioned and I kept wondering why anyone would try to fix a board. I mean, maybe if you had the skills to try and do it yourself but they're talking something like 60 bucks to replace a capacitor. Most mid range boards only cost 100, so why bother fixing it? Hell, even if a 300 dollar board blew a cap, I'd say that if it's not still under manufacturer warranty than it's at least a year old and you might as well get something newer anyway....