On Dec 4, 2005, at 3:03 PM, mi wrote:
I have two iMacs - one a G3 400, B&W, 512 Mbs RAM, 20 Gb Hard
Drive, that has fuzzy edges on it's screen. Is this a simple video
problem that can be tweaked using the information from the Mac Tech
CD, and a bit of careful adjustment, or is it a sign of the screen
about to go to where ever dead screens go?; and the second iMac is
a G3 500, B&W, 512 Mbs RAM, 20 Gb Hard Drive, 10.3.9, that takes a
lot of juggling with PRAM resets and power-on/power-offs to get it
to boot, even with a new PRAM battery, and tried with different
hard drives - which suggest a logic board problem.
Any information would be welcome.
Bob More
Bob,
First, your G3/400 iMac is exhibiting normal CRT behavior for a
machine of its age and design. I've got a half-dozen or so iMac G3s
(333-600 MHz), and they all have fuzzy edges -- some more so than
others. Those running OS X have much softer (fuzzier) screens than
those running OS 9.x because they don't have the video capabilities
to optimize OS X. The same machines have much crisper OS 9.x
displays, but still are fuzzy on the edges. I've put all these
machines through the Display Adjustment Utility procedure, which
sharpened them up a bit. They're all quite crisp in OS 9, except on
the outer edges, which is a function of CRT displays. One "trick" is
to go to the default factory image area, instead of using the
geometry tool to expand the image size to the maximum size. This
factory default was Apple's way of keeping those fuzzy edges to a
minimum. For more about CRTs, go to this extremely detailed and
informative university site: http://repairfaq.ece.drexel.edu/sam/
monfaq.htm
Next, your G3/500 may well have a logic board problem -- or one
that's just beginning to make itself known. Assuming you've also done
a cuda reset of the logic board, combined with a PRAM reset, and that
your machine isn't exhibiting any video problems (tint shifts, etc.),
you probably are seeing the beginning of heat-related logic board
failure. I don't know if your 500 has an IBM or a Motorola cpu, but
in my experience both are extremely sensitive to proper mating of the
cpu chip with the heat sink. I've seen quite a few cpu impressions on
the thermal pad affixed to the heat sink on slot-load G3 iMacs. In
those that had died of logic board failure, there was a direct
correlation between that failure and the quality of the mating
impression of the cpu in the thermal pad. There was a less than full
and even impression of the cpu in the iMacs with the dead logic
boards, which means that the cpus literally cooked themselves to
death over time. A few thermal pads were so burned that they turned
to powder when I touched them.
Apparently quality control wasn't very good during manufacture of the
perforated aluminum divider boards, to which the PAV board is
attached on top and the logic board on the bottom. Since the heat
sink is attached to the divider board (different heat sink and
location in the case of IBM 500-700 MHz G3 iMacs, by the way), any
warping of the divider board will guarantee non-optimum mating of cpu
and thermal pad.
Any time the logic board is removed, a new thermal pad should be
installed. Apple wants about $10 for an original equipment one, by
the way, which is about 10 times what you'll pay for one from an
online seller. Most sources don't recommend mixing use of thermal
grease with a thermal pad (used or new), and there's disagreement
about whether thermal grease or thermal pads are superior. Apple has
used both over the years, but not both together.
Obviously, use of a cooling fan would have helped prevent heat-
related failures in slot-loaders. But then that would have made them
noisier (their OEM hard drives are noisier than my iMac G5's fan),
and would have made all the engineering work to design a convection-
cooled machine redundant.
I don't know if this helps you or not, but it's what I've learned
about slot-load G3 iMacs ... so far.
Jim
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