Cyde Weys wrote:

V W Wall wrote:
Cyde Weys wrote:


A short from the MB to the case can sometimes cause this. Make sure any
metal stand-offs are only on the MB printed circuit "pads" that are meant
to be grounded to the case. Check any wires or metal pieces that may be
contacting the MB.

Ehh, what are metal stand offs and these circuit pads you speak of?

Just how did you mount the motherboard into the case?

The metal stand-offs are hexagonal metal pieces about 1/4' long, with a
threaded stud at one end which screws into MB mounting holes on the
case back-plane. The other end is threaded to accept a mounting screw.

On the back of the MB there are metal "pads" (exposed circuit board trace),
designed to be placed on the stand-off with a mounting screw through the
board. This grounds the MB only where it should be grounded to the case.

I've seen systems with only the little plastic stand-offs thru holes in the
MB and into slots in the back plane. This doesn't ground the MB, but
is much better than grounding it where it's not supposed to be grounded!

I've even seen systems with the MB screwed directly to the backplane!
A few even worked!!

The black wires from the power supply are ground wires, but at high frequencies
a better ground is needed, hence the mounting "pads" and the metal stand-offs.

If you had no metal mounting hardware, you'll have to look elsewhere for
a possible short to the case in the wrong place. Are there metal mounting
screws that hold the board in place?

Virg Wall