The eMac: 1.25 GHz, 256 MB, 40 GB, CD, USB 2.0, OS 10.4.11 with all updates.
S/N: G85506PTSCF, manufactured Dec. 2005 (week 50).
It was purchased by a local grammar school in early 2006 and performed without
flaw until recently. Now it has a constantly flickering/jittering screen when
it's warm. There are no smells and no sounds, just an unstable video display.
On cold startup the video jitters and jumps, and the vertical screen size
shrinks about 2 inches from the top and bottom, then slowly grows until the
Dock and Menu Bar can barely be seen. It does this a couple of times until it's
warmed up. The horizontal size, which was set using System Preferences when the
video had stabilized, does not change; it always shows a light color in the
little "dot windows" at maximum image size on each side.
Sometimes the video display stays rock solid for hours on end, going to sleep
and waking up with just a hint of flickering/jittering. But most of the time
the video display is constantly jittering, flickering and changing vertical
dimensions, which is why it was taken out of service.
It has passed every diagnostic test I could find to run on it. I even exchanged
the meager 256 MB memory stick for a known-good 512 MB stick, which made no
difference. The PRAM battery measures over 3.6 volts. I took it apart far
enough to look at all the capacitors on the logic board, downconverter board
and analog board. Everything inside the eMac looked normal: no bulging, no
leaking, no tilting of capacitors, no smells. The hard drives tests OK on the
Drive Genius 2 Scan test for bad sectors. I even did a complete archive &
install of OS 10.4.11 to eliminate a possibly corrupted video portion of the
operating system, with no change in symptoms. Booting into safe mode has no
effect on the video problems either.
I connected an external LCD monitor to the eMac, which gave me a mirror image
of the eMac's screen display. However, none of the screen artifacts, flickering
or image geometry changes that occur on a cold startup on the eMac's screen
happen on the external monitor's screen. To me, that pretty much clears the
logic board, which has the video chip and circuitry on it, of having a problem.
That means the problem lies within what Apple calls the Display/Analog
Assembly. This comprises the cathode ray picture tube, the video card on the
neck, the analog/power supply board and the flyback transformer, plus some
other little bits and pieces and cables. Apple's method of repairing any of
these components is to replace the entire assembly, which costs 2-4 times what
a complete, working, trouble-free eMac is worth on the market ($125-$150).
The strange thing is that, once it's fully warmed up and has run a while, it
sometimes is absolutely stable, with no flickering/jittering or other problems.
The screen geometry even stabilizes and stops shrinking/growing/blooming while
it's awake. It then is possible to adjust the image size and make other screen
geometry changes in System Preferences and have them remain unchanged. There is
a slight bit of jittering/image size changing when it awakes from sleep, but it
doesn't last more than 15 seconds.
My take on the eMac is that there is at least one capacitor or other on-board
electronic component in the Display/Analog Assembly that has aged to the point
where it has lost its ability to operate within its original
specifications/values when it is cold (room temperature). But as the component
or components warm up, the flickering, etc. are visual evidence of the values
changing. Finally, after as long as an hour, when everything has reached its
maximum temperature and has stabilized, the eMac sometimes performs quite
normally. At most other times, it continues to jitter slightly and the vertical
screen image blooms and shrinks slowly. The Dock and Menu Bar get pushed just
out of sight, then slowly shrink to about a quarter-inch inside the image mask.
The really odd thing is that the horizontal geometry appears to always be
stable.
This could be caused by one tiny component, or it could be an early warning of
a flyback transformer problem. It's hard to say. I'm tempted to install a new
set of capacitors on the logic board, but I'm not sure that's where the problem
lies.
I've Googled and mined the Apple knowledge base, but I've not found any similar
problems, helpful insights or fixes. Help, please!
-- Jim Scott
Eureka, CA (no, our 6.5 earthquake last Saturday is not the cause of the eMac's
problems)
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