Ah.... I see what happened now.

Here is a bit of a tale for you....

I used a little lock washer under the gecko mounting screw, it cut
thru the anodizing and connected the gecko to the heat sink, the
heat sink is connected to the chassis. The chassis is connected to
earth, earth is connected via ac earth to the the PC earth, pc earth
is also PCGnd.... created an unintentional connection between Fgnd
in the control and pcgnd in the PC.... bad noise problems resulted
in very flakey system operation.

I figured this out during the weekend and electrically isolated the
gecko heatsink - noise and control problems went away - all back to
normal.

What I did not get was why only one gecko showed a path via the
case - I found it by noticing that only one gecko's neg supply line
had a path to fgnd when the wires were disconnected from the supply.
I had thought it might be a gecko failure - but just an unlucky use
of a lock washer.

Let's all sing along now.... "The hip bone's connected the leg bone,
the leg bone's connected to the..."

Dave


--- In geckodrive@yahoogroups.com, "Mariss Freimanis"
<mariss92705@...> wrote:
>
> The mounting plate on all of our drives is hard-anodized. We use
this
> anodizing as the electrical insulation for the power MOSFETs.
Standard
> practice is to ground electronics metal enclosures.
>
> Hard anodizing shouldn't be confused with ornamental anodizing.
Hard
> anodizing is much thicker, non-porous and has at least a 3,000 volt
> breakdown voltage.
>
> The mounting plate is grounded back to POWER GROUND (term 1). The
hard
> anodizing has to be broken-thru to read continuity to ground with
an
> Ohmmeter.
>
> Mariss
>
>
>
> --- In geckodrive@yahoogroups.com, "mvcalypso" <dave@> wrote:
> >
> > I opened the gecko - it looks as if the the case and base plate
> > should be a direct connetion to the power gnd term - as the
mouting
> > screw passes right thru a ground plane layer that is not
isolated
> > from the screw hole.
> >
> > What is puzling to me is that only 1 of 9 240s I have show
> > continuity form pin 1 to the case.
> >
> > Could it be that the anodizing is what is preventing the
continuity
> > in 8 of my 9 geckos?
> >
> > Dave
> >
> >
> > --- In geckodrive@yahoogroups.com, "mvcalypso" <dave@> wrote:
> > >
> > > My mill control stopped working, I've spent the afternoon
trying
> > to
> > > figure out what the problem is... I'm still not 100% sure...
but I
> > > have found one oddity - I have one Gecko 340 where Pin 1 DC
power
> > > ground is shorted to the gecko case.
> > >
> > > The other two do not have this path. (I was running 3 rev 7
340s)
> > >
> > > For comparison, I tested some older rev 4 340s that the rev 7s
> > > replaced - none of them show continuity from DC power gnd to
the
> > case
> > > either.
> > >
> > > I'm not sure of the internal conentions on the gecko - all I
see
> > > physically connected to the base pate are the FETs.
> > >
> > > Perhaps I have a bad (shorted?) FET?
> > >
> > > Mariss, does this mean my gecko has passed on and I should
perform
> > a
> > > ritual?
> > > If so it died young, it only ran for about 3 hours run time
before
> > > going feet up. :-(
> > >
> > > Dave
> > >
> >
>