Buzzing PS?

From: Bill Girnius <thedm_at_sunflower.com>
Date: Mon Jun 9 16:48:22 1997

I have a /// for parts!

----------
> From: Doug Spence <ds_spenc_at_alcor.concordia.ca>
> To: Discussion re-collecting of classic computers
<classiccmp_at_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
> ^^^
> > > 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
which
> > > 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
>
> 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,
> 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
board,
> > 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_at_eng.cam.ac.uk
> > The gates in my computer are AND,OR and NOT, not Bill
>
> Doug Spence
> ds_spenc_at_alcor.concordia.ca
Received on Mon Jun 09 1997 - 16:48:22 BST