Date   : Tue, 30 Aug 2011 00:10:31 +0100
From   : bbc@... (Dave Curran)
Subject: eBay... sigh

On 29 August 2011 22:41, Pete Turnbull <pete@...> wrote:
>
> 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 :-))
>
Fair enough, I'll not attack it with a drill at the moment ;^)

Is that ebay 'rare' or actually rare? It says 'BBC Microcomputer Power
Supply Unit Part No. D 1597' and quotes 30 Watts, -5V @ 100mA, +5V @
2.25A, a lot lower than the standard one @3.75A.

It was from a model A, which had been upgraded to a B at some point,
and had a 1770 kit and a?Watford?12 ROM board added, the previous
owner told me it was a bit intermittent. The 5V rail was a bit low,
and when I checked the current readings it was well over 2A if I
remember, so I swapped it for one of the later switching ones, and
it's been fine since.

> 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?
>

Sorry, should have been clearer, I replace the X caps with modern X2
ones as many of the 30+ year old ones I had looked at were showing
some signs of cracking, so I'd rather err on the side of caution.

I also had one psu dead and one needing a couple of goes to start it
each time. They were both fixed by replacing C9 which appeared to have
dried up a bit and wasn't doing it's job.

Since they are a bit of a faff to get to bits and put them back
together again (and sometimes having to do it again to get the switch
the right way around!), I tend to replace C9 as well when it's apart,
and any other caps that are showing signs of leaking.

To go back to the original subject of the thread, I know it is not
preserving?them in pristine original condition, but I'd rather have
micro's I can use rather then keeping them in boxes for fear the might
go pop next time I plug them in. The BBC's were always meant to be
extended and improved anyway, so it's in that spirit I do it.

Dave