IMac display at lowest brightness after overnight shutdown

I've got an iMac 1.8 GHz running OS X 10.4.8. After the machine is shut down overnight, the screen brightness is set to its lowest setting. Going into the system prefs and setting it to high again fixes it again in the short term until another extended off period.
I tested this by rebooting the iMac (normal) and also shutting it down then starting it up again (screen brightness normal).
However, after a night or weekend shut down, the screen brightness is once again set to its lowest setting.
I've tried zapping the PRAM in open firmware. The only other thing I can think of to do is to reinstall the OS.
Any tips appreciated.

Downer. I looked at this thread because my iMac is doing the same thing. Guess I will have to keep on turning the brightness up each time.
F14 and F15 do brightness controls on my iMac; saves having to do system prefs each time.

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IMac display at lowest brightness after overnight shutdown

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