iMac G4 17" - boots, backlight, but no video

Part of the troubleshooting does involve testing the inverter board; and then it goes into
a little more than that, depends on the direction it takes...

I did find an explanation of some aspects of this (the troubleshooting steps in the pdf
do tell a pattern of testing; without a true resolution outside of parts swapping) in the
following link in a forum, from a few years ago. See what there is, in one of the replies:
http://www.ehmac.ca/mac-ipod-help-troubleshooting/38016-imac-g4-weird-boot-issue .html

quote:

Originally Posted by Lars
Mar 2nd, 2006, 09:27 PM

"Using a mini-VGA to standard VGA adapter, hook the iMac G4 up to a standard VGA CRT monitor and see if
you get an image. If you do, the Inverter Board or LCD panel itself is defective, hence no image on the main
display. It could also be a bad LCD cable or the connector on the logic board. In reality, there's a chance of 1
or more of 4 possible parts being defective..."

{A well-used iMac G4 may have some wires or connectors gone
bad, too; in addition to the other potentials. But what parts?!}

Troubleshooting would be easier if the display did not light up at
all; since you could probably tell a backlight failure easily and
then maybe figure out how to choose and use an external display.

The video circuit may have a defect; and getting into the problem
may require testing tools not available to a end user; and also
may require swapping parts in order to isolate the problem's cause.

Usually, the last item in the list of repair sequence, involves replacing
the logic board; since many things are integrated into the board, and
now these are harder to get (new, not so hard to get reman) the retail
answer is often to get the board and carefully transplant it into the iMac.

I suggest asking around and maybe even calling a repair specialist to see
what they think about how involved a repair could be, including cost(s) of
part(s) and labor. Some Apple authorized techs who do laptops also work
on these, since they have similarities; being small bits in a tight enclosure.

Best of luck in this matter...!

There is a part known as an "inverter board" but whether or not it
is still available or is not considered a part separate from the L.B.
is another story...

Do you have one of the original service bulletins on .pdf for that
model? For a time, they were online; and now only those who
bought the set (took the course, etc) or found a set online and
got them a few years ago, have the actual Service Manuals in PDF.

Since I did some extensive troubleshooting on my own iMac G4
1.25 GHz while it was under warranty (I lost six months use due
to failed troubleshooting, at 200 miles distance, and finally did
all the troubleshooting myself) thanks to Service Manual access.
Mine was a logicboard, in part probably due to an authorized
service person messing around in my iMac during RAM upgrade.

I don't think I have the pdf for the older iMac 700/800 models any more.
Those available online, unauthorized, were pulled by their owner (apple.)