Jay W. wrote:
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.


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

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?


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?

--
Adrian C