dawyd@gargoyle.uchicago.edu (David Walton) (07/29/89)
I've had this problem occur with a few machines in the lab where I
work, and I'd like to see if anybody has any input.
Hardware: Mac IIs, 8MB RAM, 68851 (originally shipped with A/UX; some
have had their partitions remapped w/o it), Apple 13" RGB
monitors w/256-color video cards, Apple standard and extended
keyboards, various internal/external Apple hard drive
configurations.
Software: System 6.0.2 with and without Multifinder, Gatekeeper 1.1.1,
some miscellaneous inits. (I don't think software is the problem.)
When I hit the on switch on the keyboard, the power to the machine and
the monitor switches on, but the machine emits an arpeggio instead of
the standard startup chord and the monitor remains black. After hitting
the reset switch, however, everything reboots just fine.
The clincher: if I shutdown completely, disconnect and reconnect the
ADB cable to the machine, and power on just as above, everything works
fine, ONCE. If I then shutdown completely and try to reboot, the
problem reappears. I've tried changing ADB cables, using different
keyboards, and booting off of floppies, and nothing seems to help.
The wierdest thing is, that after unplugging the ADB and rebooting, or
hitting reset, everything always works like a charm. I suspect that
something is screwy with the ADB (for obvious reasons). One final
note: I think this has only happened on machines that were shipped
with A/UX, but I can't swear to it.
We had one of these repaired a while ago; the repairman did nothing
except to remove a loose spring. I wasn't able to find anything when
I opened one of these things up.
Please mail or post any suggestions. If folks request, I'll summarize
to the net.
David Waltonvogelei@nmtsun.nmt.edu (Todd Vogelei) (08/01/89)
Since the Mac ADB seems to be so fragile, sensitive to long cable runs, and unplugging or plugging in devices while the Mac is on detrimental to the logic board, does anybody know of a buffer/booster unit that sould allow cable runs of 20 feet or so and would buffer the mac from nasty surges so you don't have to power down to reconnect things? ADB should be more robust along the lines of midi where you can plug and unplug stuff to your hearts content without fearing damage to components and cable runs of 25 feet are common. There's gotta be a way. Todd vogelei@nmtsun