[GRLUG] Ground drove my computer loopy.

[Bob Kline]

Useful story.  A great reminder that
right after making sure things are
plugged in,  simplify.

Thanks.  Nice bit of sleuthing.

   -- Bob


On Fri, Mar 5, 2010 at 12:38 AM, Michael Mol <mikemol at gmail.com> wrote:

> This is far and away the weirdest computer glitch I've managed to
> resolve, so I thought I'd share the story.
> --
>
> So I've spent the last seven hours trying to get my desktop to boot
> something, anything, that's a full operating system. For much of the
> time, the system was hanging randomly between POST and loading the
> boot sector, and for much of the rest of the time, it was consistently
> hanging when I tried to load a Linux kernel. I even wound up going so
> far as to flash my BIOS, because I couldn't think of anything else to
> try that made any sort of sense.
>
> The flash upgrade had gotten me to the point where I could at least
> load boot sectors again, and I was able to run memtest off of live
> CDs, but I couldn't seem to boot into 32-bit or 64-bit Linux, either
> my installed version or from a couple Xubuntu live CDs.
>
> I was beginning to suspect some sort of weird flash corruption that
> was preventing me from using graphics card features, or possibly from
> switching to protected mode or x64 mode. (I don't know how memtest86+
> works, as far as accessing all 8GB of my RAM. I'm pretty sure the BIOS
> is still in Real mode when it runs its initial sweep, but maybe it's
> bouncing back and forth between Real and Protected during POST.)
>
> The thought of another outlay to continue having a nice computer at
> home was not appealing.
>
> Finally, a few minutes ago, I realized something. I had two relatively
> new pieces of hardware attached to the computer: An APC UPS and a
> powered USB hub. I disconnected the USB connection between the UPS and
> the computer, and disconnected the hub, and rebooted the computer. The
> 32-bit Xubuntu live CD came right up. Huh. Reboot, throw in the 64-bit
> Xubuntu live CD, and *that* came right up. Huh.
>
> I haven't tried booting off my hard disk yet, and I think that'll
> require some grub command-line magic to deal with device reordering
> stemming from the BIOS upgrade and CMOS changes. However, I think it's
> ultimately workable.
>
> What I think happened is that the connection of the UPS and the
> powered hub to the computer via USB led to a ground loop that was
> messing with the internals of the USB controller on the motherboard.
> See, the powered hub isn't plugged into the UPS; it's a fair bit away
> from the computer, and I'll have to run an extension cord to get the
> UPS's power to it. As long as the operating system didn't try to do
> too much with that USB controller, things worked fine. That meant I
> could get into BIOS and tweak things, and it meant I could get into
> grub and memtest without too much trouble. Well, sortof. Remember how,
> before the flash upgrade, the system would hang at a random point
> between POST and loading the bootloader. I think the flash upgrade may
> have changed part of how it dealt with the USB controller, with the
> newer version inadvertently working around some of the
> ground-loop-induced weirdness.
>
> So, yeah. A little more experience for those weird situations.
>
> --
> :wq
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