Contact resistance in ATX power connectors causing grief

What is the response from the motherboard manufacturers? Have you approached them?

Hmmm, there is more current on the return from motherboard ground back to the supply (roughly equal to sum of currents in 5V, 3.3V and 12V rails) but I'd expect some of this to also travel back to the PSU through motherboard ground contact points (screws) and the metal case of the PSU. Check those grounding points?

What chemicals are these guys using in their factory? I'd lay some guesses that there's something "horrid" flying around in either vapour or droplet form.

Is that all hapening at one clients?

Gas tight? Any chance that moisture is being trapped inside on assembly?

Dave

What kind?? In tough spots I grab my old Cramolin vial, and or Tweek or Stabilant. The pure form of Deoxit in the tube, or Caig greese would do. And have you tried tightening the female contact going to the board. I suppose the female pin is crimped to the wire, could be faulty crimp, of course many crimps are faulty from the getgo.

Stop the fault from tripping the CPU. Bios?

Clearly it's environmental, since you can't get it to happen in the lab. This suggests something nasty in the environment. However, one thing you can check is if everything is properly grounded and you're not getting any ground loops. While it's unlikely, I can just barely envision the manipulation of replugging the connector regrounding the board.

The term gas tight is reassuring, but I wouldn't take it on faith. If the failure vs. time is relatively constant, sealing the top and bottom of the connector would be an interesting data point. A bead around the bottom where the connector meets the board, and also one at the top where the wires enter the connector. If it's a unit assembly, can you shrink wrap where the cable enters the connector?

Is there any visible change in the pins to indicate corrosion?

Jay W. hath wroth:

Are you sure it's the connector contact resistance and not the wire crimp on the ATX connector? I've seen something like this inside wafer fab tunnels, where the rather caustic chemicals attack the copper wire to solder plate junction on the connector pins. I've never seen a 0.5VDC drop. More like 200-300mv at worst. Egads,

Well, that certainly sounds like its the connector contact and not the crimp. However, I'm suspicious and will pretend that it might still be the crimp.

Have you tried to take an ohms-guesser or ESR meter and measure the contact resistance (or crimp resistance) of the connections? Also, measure the voltage drop when running between: motherboard to ATX pin ATX pin to copper wire (across crimp) Case ground to motheboard ground (just for fun).

Instead of removing and re-inserting the connector, can you get it to recover by merely wiggling the ATX connector from side to side, or doing the same with individual pins by wiggling the wires sideways? If yes, then you punching through a layer of surface crud, corrosion, oxidation, or chemical buildup of some sorts. If no, then inspect the crimp for insulation crimps, dissimilar metal issues, and corrosion.

Any evidence of copper wire embrittlement at the crimp? Heating of the connection can do that.

No. That's just solvent and light oil. Try Cramoline, De-Oxit or some oxidation prevention chemical. Also try grease or silicon grease. Anything to provide a seal.

Gas tight over what area? Verify that you have a large mating surface area and not a tapered loose fit. I've seen connector tolerances create a loose connection that eventually fails. (Hint: I designed marine radios in a previous life). Sacrifice one power supply connector and remove the nylon shell with a pair of wire cutters. Do NOT use an extraction tool for this. Take each connection and

Also, tin oxide is almost transparent and rather difficult to see. However, you can detect it with an ohms-guesser. Try passing the probe tips over the ATX plug surface, without punching through, and see if you get any insulated areas.

I think the best approach is to identify whatever chemical is attacking the connectors. I'm not sure how to do this. Also, I'm not convinced that the connectors pins are as great as you claim. Are they tin, solder plate, or lead-free solder plate? If lead-free, what substitute solder plating are they using?

What do you mean by -repaired-?

On Thu, 11 May 2006 06:18:28 -0400, Jay W. put finger to keyboard and composed:

If it's an environmental issue, try flooding the connector with the same gel (?) that telco's use for their wire joins. Or try vaseline.

- Franc Zabkar

Just a thought, I imagine each embedded motherboard has several other connectors (IDE, fan, whatever). If it's a environmental problem like a lot of people seem to think it is, shouldn't all the connectors be failing?

Lance

Jay W. thought carefully and wrote on 5/11/2006 3:18 AM:

Agreed, silicone grease fill the ATX female and fill the male side as well, this will be messy but should stop the corrsion.

On next design, make sure the crimped connections are CORRECT or use screw terminals, preferably. ITC0008 pincushion thick 3 wire plugs had mis-match gauge crimp that it is just enough to develop resistance over time or tin pins/contacts corroding. Soldering wires directly to PCB was the solution on ITC008.

Cheers, Wizard

and check the solder joints to the PWB...I have seen this kind of int. behavior due to marginal solder joints...

but it could also be the connector itself

Mark

No. The ones carrying high currents will tend to fail first. Also, connectors that carry very little current can tolerate far more contact resistance than connectors that carry high currents.

Probably right Lance, but maybe a bit of extra resistance does not matter so critically in all circuits. Also the discussion has not mentioned the necessity for good mechanical pressure in the connectors. I had extensive problems with otherwise good connectors in another set up where the spring fingers were not having or retaining their intended springiness. Also the contact material may not be as good or pure as hoped for.

Peter Dettmann

Seen this many times near plating machines and other corrosive areas with computer hardware. You have two choices: enclose and seal the hardware so that it can't be exposed to the vapor, or find a better contact coating. You have to purchase a contact coating that is specific to the metal you are protecting - lube is not what I'm talking about. In the old days, we purchase one for gold and another for silver. Now we just move the computers into safe rooms and then use video/keyboard/mouse extenders to put the display and kbd/ms in the bad areas....

I found this, it looks promising:

Different metals corrode at different rates and based on the amount of current they are handling.

Vasoline is not a good choice in an industrial location that gets any heat, it will tend to ooze/flow.

Peter Dettmann hath wroth:

Someone most certainly did mention mechanical pressure, which methinks is a big part of the problem. See:

Great Jeff, I missed that, but agree with your analysis.

Peter Dettmann