Date   : Mon, 16 Mar 2009 14:53:45 -0000
From   : mu.list@... (Mark Usher)
Subject: Dead BBC B

Are Master 128s suffering the same problem. I don't recall any postings to
the list for them, just the BBC Bs.

-Mark

> -----Original Message-----
> From: bbc-micro-bounces+mu.list=aon.at@... 
> [mailto:bbc-micro-bounces+mu.list=aon.at@...] 
> On Behalf Of Mark Haysman
> Sent: 16 March 2009 14:47
> To: bbc-micro@...
> Subject: Re: [BBC-Micro] Dead BBC B
> 
> Hi.
> 
> As I've said in another post, whenever I refurb a machine, I 
> ALWAYS replace the 2 X2s and the startup cap, even if the PSU 
> works perfect, because if I don't then the original X2s are 
> going to explode, and I'll only have to take it back and do 
> them. I'd rather get it out of the way as a preventative 
> measure, then it's done and the PSU can go on for many years.
> 
> Half a year it's been unplugged? The voltages usually become 
> safe after 5 seconds being unplugged if the PSU is okay. If 
> the switching transistor is open circuit or not switching, 
> then sometimes the DC rectified manis can be stored in the 2 
> HV caps, and it's best to discharge them - easiest way is put 
> a 60w light bulb across them for 5 seconds. Don't use a 
> screwdriver to short them unless you like sparks!
> 
> Mark.
> 
> 
> 
> > Mark Haysman posted the link to Sprow's webpage:
> >
> > http://www.sprow.co.uk/bbc/howto.htm#powersupply
> >
> > I also have a BBC B with a failing power supply. Last year 
> I measured 
> > it and found it gives about 1.2V on the 5V lines when conneted, but 
> > close to 5V if unloaded. Based on the trouble shooting above, it 
> > sounds like fault #2, the
> > BUA208 transistor which I'll try to replace.
> >
> > However, do you think it would be wise to replace the 220uF 
> > electrolytic capacitor at C9 as well as the C2 and/or C1 
> capacitors while I'm onto it?
> > The power supply didn't yet emit any smoke (that I can 
> remember) but 
> > since all three faults are somewhat common perhaps it would 
> be best to 
> > refurbish it completely?
> >
> > It has been unplugged from the mains for a half year, so I 
> expect most 
> > high voltage capacitors have discharged by now or would one 
> still need 
> > to take extra measures before digging into it? I realize 
> high voltage 
> > circuits shouldn't be fixed at all by unqualified people 
> but perhaps 
> > if one is very careful?
> >
> > Best regards
> >
> > --
> > Anders Carlsson
> 
> 
> 
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