Crispy AT Power Connector \ VOGONS

Crispy AT Power Connector

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First post, by bjt

Posted on 2015-04-12, 20:10

bjt Offline

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Recently I have been having some wierd issues with my K6-3+ system where it would occasionally randomly shut off, although the PSU fan was still running. This would normally be accompanied by a flickering picture on the monitor.

Today it stopped booting at all so I pulled it apart to find some badness:

All 4 +5V lines on the motherboard power connector are burnt. The pins on the motherboard are actually eroded, which I believe is characteristic of arcing within the connector. Pretty bad 😢 This system has an ATX PSU with an ATX->AT adaptor, and luckily the board has an ATX connector also, so I've gotten rid of the adaptor and am powering it directly now.

Any ideas what might be causing this? Cheap AT connector on the ATX->AT adaptor or deposits on the motherboard AT power connector? Interestingly the ATX connection at the other end of the ATX->AT adaptor is fine, so I believe that rules out it being purely down to overcurrent. This system has all slots filled and at one point ran a Voodoo3 PCI though.

Just glad the board still works fine via the ATX power socket, as I got a shock when I looked at the prices of decent Socket 7 TX boards on eBay.

Reply 1 of 5, by jwt27

Posted on 2015-04-12, 20:48

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bjt wrote:
The pins on the motherboard are actually eroded, which I believe is characteristic of arcing within the connector.

Most likely this is the cause, not the effect. Bad connection causes a higher resistance, which causes the pins to heat up and burn. Since s7 boards run entirely on 5V, most current runs throught these pins, so they'll heat up faster than the rest. P=I²R 😀

Reply 2 of 5, by HighTreason

Posted on 2015-04-12, 22:55

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Seems likely, given how everything powered by the connector would be considerably smaller. You'd think that if something on the board was drawing a lot of current due to breaking down somehow (like a capacitor that was going short) that something else on the board would have burnt and stability problems would be consistently occurring even after fixing the connector. Might be worth doing a quick probe around with your fingers for hot spots just to be safe though.

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Reply 3 of 5, by bjt

Posted on 2015-04-13, 09:00

bjt Offline

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Does anyone know if the ATX connector is inherently better in terms of connection quality or 5V current rating than the AT connector. I notice it also has 4 pins for +5V.

Reply 4 of 5, by jwt27

Posted on 2015-04-13, 11:47

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And 3.3V so you can actually use your PCI slots 😉

Reply 5 of 5, by bjt

Posted on 2015-04-13, 14:10

bjt Offline

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OK did some digging, seems that the AT power connector supports up to 5A per pin, whereas the (standard) ATX connector will do up to 6A.
There are high-current variants of the ATX connector too.

This is a PCI 2.1 mobo so 3.3V is optional to the PCI slots. I don't know if the mobo generates it using a VRM when using the AT power connector.

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