Date   : Sat, 12 Nov 2005 18:13:42 +0000
From   : Annihilannic <annihilannic@...>
Subject: Re: Guess age from serial number? - Holy smoking Beebs,

Thanks for all of the replies folks, just replying to this one since you 
all suggested more-or-less the same things.

I don't find time to play with the Beeb very often, hence the long gaps 
between posts...

Jules Richardson wrote:
> *usually* when you get lots of white smoke and that noise it's the noise 
> supression capacitors that go aross the mains input on most power 
> supplies. I can't remember if the beeb has them or not, but I'm willing 
> to bet that it does. Look for rectangular yellow capacitors near to 
> where the mains enters the power supply - if one's failed it'll be 
> obviously cracked open, often leaking a bit of brown goo.
> When one fails they generate a *lot* of smoke! For some reason they 
> usually seem to fail as you described too - not when the machine's 
> switched on, but sometime later. We're finding a lot of them dying these 
> days in vintage machines of all types.
> They're there primarily to stop the device (the beeb) from contaminating 
> the mains with lots of noise and upsetting other mains-powered devices, 
> which is why the beeb carries on working fine without.
> I'd still replace them though - modern ones which will hopefully last a 
> lot longer are available from Maplins and the like.

After a bit of searching I located those capacitors with the help of the 
clues Mike Foot posted, marked in blue on the photo here (one of them is 
hidden under those wires and connectors).

http://galaxy4.net/misc/beeb_power_supply.jpg

They both look healthy from the outside?  What *does* look odd are the 
brown parts on the transformer (marked in green) and the widget beside 
it (marked in red) which look like dried honey... or spilt black coffee. 
  I presume the transformer is where the smell and smoke were coming 
from; does that sound likely?  Easily fixable?

>>Could this PSU be one of the ones you were talking about?
> It was probably just that capacitor's time to go - as I say, we're 
> finding a lot of them blowing in old machines these days. I'm not sure 
> if the failure's simply age-related, or due to the parts being 
> under-spec (often they're rated at 250V which might be a little close to 
> mains input for comfort, and years of running close to the limit kills 
> them. Modern replacements seem to always be rated at 275V instead)

I wonder could running it on 220V power here in France be a problem?

> It's hard to outright kill a switchmode power supply like the one found 
> in the beeb. Even if outright short something such power supplies tend 
> to just go into shutdown mode.

I can but try!  :-)

-- 
Annihilannic