Hello folks,

I am having a rather unusual problem with about six hundred embedded
motherboards in the field, and was hoping someone might have an idea (or
two) on what might be happening, and possibly what the fix might be.

These are embedded low power Via C3 based motherboards that are deployed
in the factory automation industry. Power is distributed from the power
supply to the motherboard through a 12" power cable which consists of (2)
18ga. ground wires and (2) 18ga. +5VDC wires to an ATX style connector on
the motherboard; the board draws about 3 amps of +5VDC under maximum CPU
load. After several months in the field, contact resistance on the ATX
connector increases for some reason, and is causing a voltage drop as seen
on the motherboard (sometimes as much as .5VDC!) There is an onboard
voltage monitor on the CPU board that triggers a reset at about 4.7VDC,
the end result being that the processor gets stuck in a reset loop - it
will run for a minute or so and then the CPU load momentarily increases
and resets again. The voltage drop is *usually* greater across the ground
lines than the +5 lines for some reason. Maybe there's a clue there?

On a system that is failing, unplugging the ATX connector and reseating it
will "fix" the problem and the system will continue to work for several
months until once again the resistance increases in the contacts and...
well, you get the picture.

If the connector is reseated here at the factory and "repaired", we cannot
get it to fail again under any conditions: vibration, humidity,
temperature cycling in a environmental chamber, etc.

We've tried using contact lube - no luck.

Thinking that there might be a problem with dissimilar metals, we checked
that the contacts on the cable and ATX connector on the board are tin. The
contact specification claims that they are gas tight.

At first (a number of months ago) we were seeing only a .2 to .3VDC drop,
so we increased the power supplies output to 5.15VDC hoping to compensate
for the drop (a Band-aide, I know), but as you can see above, the contact
resistance kept increasing only to have the same problem occur.

We cannot increase the gauge of the wire, nor can we add more +5 and
ground wires due to there being only 2 pins available for each on the
power supply. The crimps will not accept double crimping.

I know the problem could be solved by soldering the wires between the
power supply and MB, but this would be a huge task due to the number of
units in the field, and the difficulty of disassembling the systems,
pulling the boards, and reworking them.

Does anyone have any thoughts on what is happening here, and possibly an
easier solution?

Thanks very much for any help.