Powerbook power adapter keeps switching on and off

Hi,

I have a 12" Powerbook 1 ghz (yes, it's getting old) running Tiger. When it's turned off, it charges just fine. However, when the computer is on, the power from the adapter keeps cycling on and off. For example, the lighted band around the power adapter tip switches from orange to off (NOT to green) repeatedly: about 3-4 seconds with power (lighted band is orange, screen backlight is bright, and if I'm in the Energy Saver section of the System Preferences, it thinks it's plugged in) and about 1 second with no power (lighted band is off, screen backlight dims, and if I'm in Energy Saver area, the computer thinks it's on battery power.

This is irritating because 1) the computer won't charge when on, and 2) as I type this, the screen goes from bright to dim to bright to dim etc.

Obvious answer is the power adapter, but I don't have access to another. What does everyone think? is it the adapter or some other problem?

FWIW, the internal hard drive just died and I'm booting from an external FireWire drive. It started doing this power thing a few days before the internal hard drive died.

Thanks for any help you can offer!

- bb

One more data point

One other thing to add to my original post. If I take the battery out and just try to run on AC power, the indicator ring on the power tip lights up green. However, after the startup chime, the computer makes it to where the little circle is spinning around while booting up (about 10 seconds after powering on) and the whole thing shuts off.

I think this is consistent with the power adapter being the problem (definitely rules out the battery). Don't know what an SMC is but will look it up.

- bb

EDIT: Looked up SMC and I think my computer's too old to have either an SMC or the earlier SMU. Think mine may have a PMU instead and I'll try resetting it when I get home tonight using SCOP (http://en.wikipedia.org/wiki/Power_Management_Unit).