[ltp] odd power problem

[David Guichard]

I'm running linux (fedora 5)on an R51. Recently it started having
power problems and the details are a bit odd.

If the laptop is unplugged from AC, it immediately shuts down and
tries to reboot--not a nice system shutdown, but like pulling the
power completely.

On battery only, it won't boot. It gets through grub fine, but as soon
as it says that it's booting the kernel, it switches off, then tries
to reboot again. Occasionally it gets somewhat farther before
crashing. This crash-reboot appears to continue forever. Plugging in
AC again allows it to boot.

Nothing in the logs that I can see--not surprising given the speed of
the crash.

On battery alone, it will boot fine from a live cd, like knoppix.

The battery is getting old, and doesn't provide as much time as it
used to, so that was my first guess. I have an R52 with what appears
to be an almost identical battery in very good shape. I tried that
battery, and the behavior was the same.

Then I tried reinstalling the operating system--maybe that would avoid
some bad blocks? No help.

Then I tried swapping the drive from the R52 into the R51. As I went
to do that, I noticed that the retaining screw on the drive had gone
missing. With the R52's drive in, it worked fine in a brief test. So I
reinstalled the original HD (including a screw) and it worked
fine. Problem solved, yes? Apparently the drive just needed to be
reseated.

Well, no. A few days go by, and it starts doing the same thing
again. I tried reseating the HD a few times, no help. smartd reports
no problems with the drive. I put the R52 drive back in the R51, and
the bad behavior persists.

So finally I start poking around in the bios. Eventually, I changed
the "CPU power management" setting from automatic to disabled, and the
problem disappeared. When I set it back to automatic, it crashed
trying to reboot; back to disabled and it's fine again. It will boot
on battery and pulling the AC doesn't crash the machine.

Anybody know enough to explain why this matters when running on
battery from HD, but not from CD? Is it likely that this will not be a
permanent work-around?

-- David