Hi,

I seem to have a problem with an old iMac G3 400 MHz...

It seems to be fully functional, aside from a completely
dark screen. So I thought maybe someone tried to install
OS-X on it without updating the firmware...

When I push and hold the button in front, as it shuts
down, the screen briefly is bright and clear with desktop &
icons.

Being a model with an external VGA connector at the
back, I plugged in a monitor on it and the image is OK...
So I reinstalled MacOS9 up to 9.2 and then updated the
firmware successfully to 4.1.9.

So I have a fully functional iMac updated to 9.2 and with
correct firmware, but the screen still remains dark. I see a
very very faint dark image on the iMac's screen of what's
on the external monitor but that's it.

Restarting it without the external monitor gives this faint
image of the desktop, and shutting it down by holding the
start button again gives this bright, clear image for a
quarter of a second... So the tube seems to be good...

Is the screed fried? Is there something that can be done?

It's a good little iMac and I would hate to chuck it, because
a good friend would benefit from it to get her email and
surf the web...

Robert, in Montreal

Seems like Brigtness controll or LOT problem. Can you confirm this with a CRT repair Technician ?.

Have you tried booting with extensions off ?

I had this exact same problem a few years ago and fixed it
by replacing the backup battery. Why a flat battery should
make the screen go dark I don't know. There was no
mention of this in any of the troubleshooting solutions for
iMac G3. But it has worked for others too so it's not just a
coincidence in my case.

Namari
Inverness, Scotland