other
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Fried SCSI bus with a side of grits. Help, please.
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Dec 5 05:03 UTC 1999 |
I think my SCSI bus fried. Help me figure this one out if you can. Here are
the details:
Machine:
Macintosh Centris 640
Motorola 68040
Mac OS 8.0
Symptoms:
At startup, i get the disk icon with the flashing "?" symbol.
When I tried to force boot from a CD-ROM, i got the black screen with
the sad mac face and these two lines under it:
00000F
000001
The machine also will not seem to be willing to allow a force boot from
a floppy, because as soon as i put one in, it spits it right out again, or
if i start the machine with one in, it spits it out as soon as it powers up.
(I may have the force boot keys wrong. i can't find a reference. if you know
what they are, please post.)
I swapped out the hard drive for another one, and nothing is different.
(The drives i swapped have both successfully booted this machine
before.)
Any questions, comments, suggestions? How can i determine with certainty
whether the problem is the SCSI bus? Is there anything I can do about it,
or would i have to put in a new motherboard? (or buy a new computer, since
the replacement wouldn't be worth it for a 1993 machine.)
Thanks!
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mdw
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response 1 of 2:
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Dec 6 06:23 UTC 1999 |
I think you need to find out what the numbers mean. I don't believe the
floppy is on the scsi bus, so if you can't boot from floppy either, that
suggests some other more major problem. Perhaps there's an error with
low memory, a fault with the DMA logic, or some other serious problem.
First thing you might check is cabling. The next thing you might check
is memory -- you might start with taking out all the memory, then trying
with 1 module at a time. I don't think the 68040 needs pairwise memory,
so this should be sufficient. Try each memory chip by itself. If you
have a voltmeter, something else you might check is the logic level for
+5 and +12. If you have an oscilliscope, you might also check for
ripple on these lines. A bad power supply could easily result in the
motherboard operating properly (since it only needs +5) but improper
operation of peripherals (which often need +12).
Unless this is your personal machine, it may not be worth spending a lot
of time on this. If you want to fix it, you might find it worthwhile to
visit UM property disposition (or elsewhere) to pick up a used centris
and swap parts. Of course, there's every chance if you found another
centris, that it might have the same dead part as yours - if there's
some sort of family weakness in the product.
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