Problem with displaying any picture at all.

Question

Hi there, one of my iMacs has a problem with displaying video.
When I turn the computer on the screen shows a yellow-orange hue in the centre, and it's getting wider across the screen and bright, eventually it turns to a white screen. Now I know for a fact it's nothing to do with the logic board! I can control the computer with remote desktop and dim the screen or make it brighter. My question is, is it the cabling that is faulty or something else?
If it's the cabling, how can I open the chrome neck and change it?
Thanks you

Answer 1

Did your testing include utilizing a second display and adapter to see
how a mirrored output of the video would appear; to be sure this item
is isolated to the wiring from the circuit boards to the attached LCD?
There are components within the border of the iMac G4's display which
may affect the image as they wear out and/or fail. The inverter, is one
item that is in the panel along with the backlight and liquid crystal layer.
Removing or replacing the wire harness between these components,
the computer base and LCD panel, is a bit of work. This topic has been
addressed in these forums at one time or another; and a few owners
who contribute here have experience taking these apart. In the past,
getting a known-good display with chrome arm and harness, from an-
other iMac (perhaps one with logic board failure) and combine two,
was an answer when the complete display & arm were known good;
as this saved a fair amount of work on the upper end. Still, taking the
lower orb shape apart is a significant task; to have it work right again.
The cabling could be faulty; the inverter could be. And there may be
yet another associated component failing which produces symptoms.
Taking apart the chrome arm may not be such a good idea; I've seen
the expanded view of one taken apart by a metal cutting saw, and it
has a big spring inside, and a bit of tension. There also are friction pad
parts inside that loose their ability to hold up the panel, so some owners
sought to replace those to varying degrees of trouble.
There should be a few step-by-step instructions. One of the contributors
to the iMac G4 forums here was Mr Totes; one of his web pages had a
few images of take-aparts he'd done. Other sites had basic stuff, such
as replacing optical drive and hard disk drives, thermal paste, RAM, etc.
If you were able to see the correct system images from a second display
via the VGA adapter cable, in mirror mode, the attached unit certainly is
suspect; and the computer is probably repairable. Otherwise, there is a
video component on the logic board not considered a separate part; and
if that fails, the usual fix is to get a reman logic board or another iMac.
Have fun, whichever way it goes.
Good luck & happy computing!