PC is dead after installing new board

  • Thread starter Thread starter Bob H
  • Start date Start date
Only one standoff must connect motherboard ground to chassis
ground. Intel specs for PCs put numerical specs to area in
which this connection (conductive standoff) should be
located. It is typically the standoff hole between IO card
slots and power supply connector. Another permitted standoff
was located in the PCI slot region.

Why only one ground? Currents do conduct across the chassis
plate. If motherboard is grounded to chassis in multiple
locations, the currents would also flow through motherboard
ground plane creating voltage differences (noise) between IC
on that motherboard. We would demonstrate this problem by
putting a computer on a glass table and static electric
shocking the chassis. That static electric discharge (that
flow across motherboard with multiple conductive standoffs)
would cause the OS to crash. Better computer stability means
only one path exists between computer motherboard and chassis
plate. With only one connection (without both an incoming and
outgoing path through motherboard), then electric currents in
a chassis do not pass through motherboard.
 
David said:
I'd be willing to bet that, even though I'm sure he's checked, there's a
standoff in the wrong place underneath as it's easy enough to do.
Click to expand...
Yes, that was the cause, doh! All sorted now
 
w_tom said:
Only one standoff must connect motherboard ground to chassis
ground. Intel specs for PCs put numerical specs to area in
which this connection (conductive standoff) should be
located. It is typically the standoff hole between IO card
slots and power supply connector. Another permitted standoff
was located in the PCI slot region.
False


Why only one ground? Currents do conduct across the chassis
plate. If motherboard is grounded to chassis in multiple
locations, the currents would also flow through motherboard
ground plane creating voltage differences (noise) between IC
on that motherboard. We would demonstrate this problem by
putting a computer on a glass table and static electric
shocking the chassis. That static electric discharge (that
flow across motherboard with multiple conductive standoffs)
would cause the OS to crash. Better computer stability means
only one path exists between computer motherboard and chassis
plate. With only one connection (without both an incoming and
outgoing path through motherboard), then electric currents in
a chassis do not pass through motherboard.
Click to expand...

The motherboard already has more than one ground even with your erroneous
'single standoff' theory: the standoff and the PSU ground wires (multiples).

A 'single point' ground doesn't work at high frequencies because the wire
length is significant relative to the wavelength and becomes an antenna.
 
Bob said:
Yes, that was the cause, doh! All sorted now
Click to expand...

Ah, good. You found it.

As I said, it's easy enough to do and is 'invisible' once the motherboard
is over it.
 
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