Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!uunet!mcsun!ukc!icdoc!qmw-cs!davide
From: davide@cs.qmw.ac.uk (David Edmondson)
Newsgroups: comp.sys.mac.hardware
Subject: Re: ADB and blown motherboards
Message-ID: <1738@sequent.cs.qmw.ac.uk>
Date: 2 Mar 90 15:17:35 GMT
References: <1494@key.COM>
Reply-To: davide@cs.qmc.ac.uk (David Edmondson)
Organization: Computer Science Dept, QMW, University of London, UK.
Lines: 40

In article <1494@key.COM> jbr@hongkong.key.COM (Jeff Rubin) writes:
>
>It was reported by several people that it is unsafe to plug and
>unplug ADB devices when the Mac is powered on.  Some have even
>reported blown chips on the motherboard that were attributed to
>this type of manipulation.
>
>I'm not sure which machines my question pertains to, so I will
>phrase it in terms of my Mac IIcx.  The keyboard (Apple extended)
>has a button with a triangle on it that I use to turn the power
>on.  Since the keyboard is an ADB device, does the power-on
>mechanism use the ADB?  If so, does this imply that ADB has power
>even when the rest of the machine doesn't?  Does that mean that it
>is not safe (just as unsafe?) to plug/unplug ADB devices when the
>power is off?  Do I have to pull the plug from the wall before it

No.  In the MacII the fuse that blows is for the +5V supply,
the power on line is a different circuit which uses the
internal batteries to wake up the main power supply (this is
why Modular Macs will not start if they have a flat battery).

So the machine must be shutdown but you can leave it plugged
in.  I would dearly like to know if this problem has been fixed
in later models, our students seem to have a habit of yanking
out keyboard cables on IIcx but none of them has killed the ADB
(yet).

See Apple Macintosh Family Hardware Reference Guide Chapters 19
and 23.

-- 
David Edmondson

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