Date   : Mon, 29 Aug 2011 22:41:15 +0100
From   : pete@... (Pete Turnbull)
Subject: eBay... sigh

On 29/08/2011 18:01, Dave Curran wrote:
> Just whilst we're on the subject of power supplies, I tend to replace 
> C1,C2 and C9 as a matter of course after a few went pop a couple of 
> years ago. 
> 
> However, I've got an issue 3 machine with the old black linear power 
> supply. This is riveted shut, so I haven't done that one. Do they have 
> those sort of filter caps in, and is it worth drilling out the rivets to 
> replace them?

There are three quite different versions of the black linear supplies, 
and it's possible some have suppression capacitors.  I wouldn't take it 
apart, though.  For one thing, linear supplies rarely have X2 or Y2 
caps, and for another it's actually fairly pointless replacing those 
things until they go.  X2 and Y2 caps aren't like electrolytic 
capacitors that age, dry up, etc.  Even the electrolytics will be fine 
unless overheated and mistreated.

One of the black power supplies was internally known as "the adapter and 
exploder" (it had a label with some name and "adapter" on it) because it 
tended to do just that.  Those linear PSUs were only really any good in 
Model As without disk interfaces; they don't have the grunt for much 
more.  Acorn replaced them FOC if you had a disk interface, a ROM 
upgrade, a second processor, a decent haircut[1], or just about any 
other half-decent excuse.  As a result, they're R at R3 and should be 
preserved intact (and away from AC voltage :-))

I confess I'm not exactly sure what caps you're referring to.  C1 and C2 
are X2 caps, C9 is one of several electrolytics.  If you're going to 
replace C9, why not C6 and C8?

[1][ The definition of that might have been different in the early '80s.

-- 
Pete                                           Peter Turnbull
                                               Network Manager
                                               University of York