Mike De Petris wrote:
On Aug 13, 9:54 pm, wrote:
Have you looked at the MB power bus (+5v I would assume) for ripple
when you attach the external power supply?

this is what I am asking for, I tought I should measure it at the
socket pin holes, how can I idetify the +5V line on the motherboard?

My guess is the hard drive is operating on +5v. You could measure it
there.

And how would you measure (and fix the cause) a ripple on the bus? I
have a couple of scopes and multimeters for that, but how?

First determine if it has ripple. You can normally take a volt meter
set for AC and measure the ripple on a DC bus. Old VOM's used a cap to
isolate the AC from the DC component, but the new DVM's generally work
for this. If you did find ripple, look for a cap that is bad or
possibly a diode that is shorted. First determine if it exists.