Path: utzoo!attcan!uunet!husc6!mailrus!cornell!calvin!johns
From: johns@calvin.EE.CORNELL.EDU (John Sahr)
Newsgroups: comp.sys.mac
Subject: Re: crash and burn!!!  Why no fuse?
Message-ID: <561@calvin.EE.CORNELL.EDU>
Date: 16 Aug 88 20:49:31 GMT
References: <870209@hpcilzb.HP.COM>
Reply-To: johns@calvin.ee.cornell.edu.UUCP (John Sahr)
Organization: Cornell Space Plasma Physics Group
Lines: 24

In article <870209@hpcilzb.HP.COM> tedj@hpcilzb.HP.COM (Ted Johnson) writes:
>
[]
>But it makes me wonder..., WHY DOESN'T MY SE HAVE A FUSE?????
>Seems like the $.50 that a fuse costs would be worth it!
>Maybe someone at Apple can answer this...?

I hope that someone at Apple will answer.  However, the power supply in
your SE or Mac II is unusual in that it will "eat" 110-240 volts without
flipping any switches.  It is a "switched-mode" type of power supply.
We have run our Mac II on US 60 Hz 110 volt, and then plugged it into
the Scandinavian power grid (50 Hz, 220 Volt).  We did nothing but plug
it in both times.

Because the transistor/diode switch would probably blow up faster than any
fuse if it failed, it might be pointless to put even a $.50 fuse in the
SE or Mac II.  There is very likely to be DC isolation from the AC grid
in the form of a small, high frequency transformer.  

I am just guessing, based on what I've learned about these type of supplies.

I am not affiliated in any way with Apple.

John Sahr (johns@calvin) [opinions expressed are my own alone]