Why iMac goes into coma booted in Ext HD Tiger hot plugging USB cable?

Question

Folks:
Had this question posted as "iMac goes into deep coma w/hot plugging USB cable??" on the "using your iMac G4" forum, got 63 views but have not received any replies there. Since I was booted up in Tiger 4.11 on my FW Ext HD, thought I'd try to post over here to see if I get some sage advice from this forum.
Was trying to experiment with ways to get my scanner to work if I finally decide to upgrade my iMac to 10.4.11 by booting up Tiger using External HD by firewire and then plugging in the scanner after that. As soon as the USB plug touched the port the computer "went black"--total crash. Took about 5 mins before I was able to resuscitate the machine with the power button. I repeated my experiment in the same manner and down she went again, down and out . . . . Tried to start it for a few minutes, nothing, went to dinner, came back, nothing. Finally, unplugged it for a minute and then she came back to the land of the living . . . .
When I restarted from the 10.1.5 internal HD I plugged the scanner in and opened the scanner app in Classic and all was fine. I like being able to use Classic apps and if it wasn't for the fact that my Camino browser is starting to crash when browsing the newer websites I'd have no reason to upgrade. Even if I get a new Intel computer I won't be able to boot back into the Power PC operating systems, right?
Anyway, would like to know if it is "well known" that you can't hot plug peripherals when booted up in external HD or if this is a "special problem" that only I am experiencing?
Thanks,
e.e.p.

Answer 1

Since the issue could be in the peripherals or the computer involved, this could
be a hardware failure of some kind. If you have replaced the USB cable, and all
other variables have been double or triple-checked, even a problem with the
computer's power supply could be at fault. Or there may be a partial short in one
of the electrical circuits involved with this USB cable and whatever it supports.
Please re-explain these other operating systems and their locations, since the
10.1.5 and other stuff seems irrelevant. Unless there is a hardware failure.
And that is a possibility.
If you got an old early model Intel mac with 10.4.11 running in it, that would not
support Classic OS9 based apps directly. However, there are several sources
for replacement parts and also complete repaired and guaranteed PPC Macs.
There are limits in some, in what OS X versions and practical uses they may
allow now, with less online support & dwindling apps to run on the older OS X.
You may be able to look into the system logs and crash reports, via Console
Utility, to see what kinds of errors reports & crash logs the computer created.
Also, in System Profiler, there should be a Software> Logs section and it may
have some recent activity logs there. You can compare log creation times with
the intervals of these failures and see if a report matches your experience in
a real-time error log or other.
Is this USB port where the failure occurs, located in the external drive enclosure
or in the computer attached to it? What kinds of external FireWire devices and
USB devices are involved? Have you ran just the bare-bones computer & seen if
there are problems in just that, by itself? Troubleshooting invites checking it alone.
If there is an overload of some kind regarding a power supply failure under
only some circumstances, you could try a powered USB hub when using
several items attached to the computer; so it would carry that load.
Anyway, it sounds like a magical mystery tour is in store, in there.
Good luck & happy computing!
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