Jeff Walther wrote:
Date: Thu, 17 Nov 2005 10:50:06 +1300
From: Richard Halkyard <[EMAIL PROTECTED]>
I've recently acquired a PowerMac 6100 with the DOS card installed, and
it seems to be acting up. It has a fresh PRAM battery, but will
sometimes act as if there is no battery (startup chime but no display),
and then act fine with no data loss later. When it is running, it will
occasionally lock up, with coloured pixels randomly flashing in the
top-left of the display. I've tried swapping and removing all the bits
and pieces - DOS card, cache, RAM, hard disk, CD and everything. Its
driving me nuts, because I rather liked the idea of having an (old) PC
and Mac in one. Any ideas?
I've seen similar symptoms in several 7100s and the cause is
overheating of the CPU chip. In those cases, the CPU chip was
overheating because the heat sink grease had dried out and was no
longer doing its job.
It's not a certain diagnoses for you, but it's fairly easy to test and
will only cost you $2 - $3 and a trip to Radio Shack if you don't
already have some heat sink grease on hand.
Remove the motherboard from the machine. Carefully unclip the heat
sink (push the tabs out from the back of the board). I write,
"carefully", because putting undue downward pressure on the heat sink
has been known to *crack* the CPU in several cases.
There will be a white residue on the CPU and on the heat sink.
Originally this stuff should have been nice and creamy. At this point
it is probably dry and powdery. Gently clean it off using rubbing
alcohol (70% isopropyl) or 90% isopropyl and some kind of swab. In a
pinch Q-tips or cotton balls are okay if you're careful not to leave
little polyester fibers everywhere. Clean it off of both surfaces.
Let them dry.
Heat Sink grease is available from Radio Shack for $2 - $3. It comes
in a little blue and white tube on a card which is usually hanging on
a peg board. Sure, you can spend $15 on Arctic Silver, but the RS
stuff does the job well enough.
Apple a little dab on the square metal die in the center of CPU. Do
not overapply. Heat Sink grease is mildly electrically conductive and
if it runs off of the chip onto the pins of the CPU it can cause
shorts. I killed a Power120 that way once. The grease just needs to
fill the tiny spaces caused by the CPU die and the heat sink not being
perfectly flat surfaces.
Carefully clip the heat sink back into place. Try not to slide it
from side to side when installing it. Shoot for a straight approach
to the CPU without a lot of side to side sliding. Coming in with the
heat sink angled a bit, so that two clips go into their holes before
rotating the heat sink down so that the other two clips hit their
holes often works well.
Resinstall your motherboard and test it out. You may also wish to
consider installing a little fan on the heat sink. The fans typically
bolted to 80486 heat sinks could be unscrewed and fit nicely in the
center of the x100 heat sink. Use small cable ties (also available at
Radio Shack) to secure the fan to the heat sink tentacles through the
fan's screw holes--i.e. the cable ties go through the fan's screw
holes and around one of the arms of the heat sink. You can suspend
the fan just above the flat heat sink surface this way.
Date: Wed, 16 Nov 2005 22:00:52 -0800
From: "Matthew S. Carpenter" <[EMAIL PROTECTED]>
I tried to grab it but still ended up dropping it about a
foot... Anyway when I brought it to the lab upstairs I couldn't get the
damn thing to glitch out...Gad, it made me look like an ass.
Probably jolted the heat sink about just enough to make better contact
with the CPU. Perhaps rubbed some of the powder into a better position.
Jeff Walther
I completely forgot about this.... but my dad put a peltier heatsink in
my 6100... The idea is that it uses electric current to pull heat from
the powersupply into the heatsink faster. You can power the heatsink by
soldering it's leads the power socket on the motherboard.... at least
that's what my dad did. (just make sure you hook it up to power right,
or you won't be very happy with the end results)
Shreve Systems sells them in bundles of 5 for $10.
-Matt
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