orange sparks where psu connects to motherboard

[zeta_r_123]

One of my mining rigs was mining successfully for about 6 weeks. Yesterday, I found it silent and not running. So I switched off the psu and then turned it back on.

Immmediately, there was a large orange spark in the the area where the psu connects to the motherboard, so I shut it off and took apart the rig to inspect the connector and pins, to see if anything was obviously burned out. To my untrained eye, the pins and connector look okay, but obviously I am only seeing what is visible from the outside.

Another strange thing that I noticed in the weeks leading up to the spark- my psu would occasionally make subtle clicking sounds (one click every couple of seconds), almost like the sound of water dripping.

Is this an obvious short on the Mobo or can it have something to do with the psu? I am hesitant to try out another psu with the same mobo.

My hardware: 4 x sapphire 7950's- two on the mobo, and two with unpowered risers (I suppose this could have overloaded the mobo). psu is a Corsair AX1200i, and the mobo is an MSI 990-FXA GD65.

Thanks in advance for any suggestions.

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[m3]

what connector are you talking about? is it the big 24 pin or the 8 pin cpu one?

[zeta_r_123]

It was the big 24 pin connector.

[phillipsjk]

I would expect a burned-out component on the motherboard.

I would expect poor contact to cause blue sparks.

Of course, if orange implies fire, I would expect smoke as well.

[justbtcme]

PSU making clicking sound would indicate to me the coils in it could be burning out or getting dirty somewhere. I would replace the PSU right away, to avoid any possibilities of a fire.

[phillipsjk]

With posts about hot cables, I am wondering about cracks in the insulation due to excess power draw.

Do you have more than 3 video cards mounted on the board by any chance (without powered risers)?

My hardware: 4 x sapphire 7950's- two on the mobo, and two with unpowered risers (I suppose this could have overloaded the mobo). psu is a Corsair AX1200i, and the mobo is an MSI 990-FXA GD65.

I would suggest either pulling two cards or using powered risers. You should replace the 24pin connector as well (which likely means replacing the whole power supply).

[zeta_r_123]

I had 4 cards, 7950s, on the board. Two sitting on the motherboard, and two with unpowered risers.

Shouldn't the psu be able to handle that kind of load without the insulation cracking. I suppose I could try a new psu, but I am a bit afraid to plug it int the motherboard- what if the motherboard is the problem. Don't want more sparks. Perhaps I should replace both psu and motherboard.

[phillipsjk]

The 24 Pin connector only has 2 12 Volt wires. You are not supposed to install that many power hungry cards in one board.

The Molex Mini-Fit Jr. has a power rating of 600 volt, 13 ampere maximum per pin[11]

[zeta_r_123]

Can you help me with the math, tell me if you think I am right or wrong:

13 amps per pin x 2 pins x 12 volts = 312 watts.

Each card draws about 190 watts, according to:
http://www.tomshardware.com/reviews/radeon-hd-7950-review-benchmark,3207-9.html

They get their power directly from the PSU and also through the mobo.

I think I read somewhere that the PSU supplies about 150 watts directly to the card (not sure of that is correct or how it matters whether:1) I use one 6 pin connection at the PSU split into 2 6 pin connectors at the card or 2) 2 separate 6 pin connectors. I am pretty ignorant).

So each card draws about 40 watts (?) through the mono. times 4 is 160 watts. I have the OS on a flash drive (no HD), and a low watt CPU, probably consuming about 100 watts.
Not sure how much watts the fan is drawing. I guess I am cutting it close to the 312 watts, perhaps over if I am off in my numbers.

Any thoughts?

Thanks for all the help so far!

[phillipsjk]

Can you help me with the math, tell me if you think I am right or wrong:

13 amps per pin x 2 pins x 12 volts = 312 watts.
...
Any thoughts?

Thanks for all the help so far!

Apparently for a 24pin connector. 18 gauge wire, the limit is 8.0 Amps.

On another wikipedia page, it is mentioned that the current rating given assumes a 30°C temperature rise (not sure where to find a citation). That means that if your machine is running at 40°C, your cables will be at 70°C. Depending on the cable, the wire insulation may melt at only 85°C. Edit: I think most chassis wiring is rated for 105°C. In any case, it is usually printed on the cable.

I worked out a possible fix: If you are able to find a way to disconnect the wires from the connector, you can put heat-shrink tubing over each wire (assuming you found any breaks). I was able to do that once while converting an old DELL supply to the ATX standard. Tried again years later and was not able to do it. IIRC, the pins use springs to stay in place.

The limit I have been using for ATX power: 5 amps per wire pair.
Edit: splitters are bad news. You want wire pairs going all the way back to the PSU.