9 Jun
1997
9 Jun
'97
4:48 p.m.
I have a /// for parts!
----------
OK, here's a question from an electronics-know-nothing (which hopefully
isn't in the FAQ, else I'll look like a complete idiot :) ): How do I
tell the difference between a switching supply and a linear supply? Just
from looking at it.
I get the idea that linear supplies have honking big transformers in them,
board,
From: Doug Spence <ds_spenc(a)alcor.concordia.ca>
To: Discussion re-collecting of classic computers
<classiccmp(a)u.washington.edu>
Subject: Re: Buzzing PS?
Date: Monday, June 09, 1997 4:21 PM
On Fri, 30 May 1997, A.R. Duell wrote:
> > Hi,
> >
> > The Apple /// I picked up last weekend has one annoying flaw, and
that
is
^^^
which
> a *very* loud power supply, that seems to
get louder the longer the
> machine is powered up.
<snip>
> > Is this noise normal, or is it a sign that something is about to go
> > kablooie? And if something's wrong, is there any way of knowing
part is about to go?
No it's not normal. The Apple uses a switching type supply, and there
shouldn't be any 60Hz waveforms anywhere after the mains
rectifier/smoothing cap. If it's buzzing there is a problem and switching supplies don't.
> It _may_ be nothing more than the mains filter coil (if it has one), or
it
> may be a dried up smoothing capacitor (the 2 big
ones rated at about
300V)
that needs
replacing. You could try those first.
I don't remember there being any very large capcitors. (Nothing like in
my PET 2001, anyway... hooo boy! ;) ). I'll take another look inside to
see if I can spot the ones you're talking about.
<snip>
> Apple PSUs are easy to check. The 6 way cable unplugs from the main > and the wiring is given in the Apple ][ reference
manual. Just connect
a
> voltmeter between the +5V output and the ground
wire (red and black?)
and
power up. I
don't think you need a dummy load. If you don't get 5V when
you power up, you need to sort out that PSU.
Well, the ][ and /// use different connectors, but I noticed that the
///'s supply has info on the PCB.
The supply works, BTW. As I mentioned, the system powers up and runs as
if nothing were wrong. The noise the power supply makes just makes me
nervous.
--
-tony
ard12(a)eng.cam.ac.uk
The gates in my computer are AND,OR and NOT, not Bill
Doug Spence
ds_spenc(a)alcor.concordia.ca