Date : Sun, 22 May 2005 14:01:11 +0000
From : Jules Richardson <julesrichardsonuk@...>
Subject: Re: "Pop goes the Master 128"
On Sun, 2005-05-22 at 13:13 +0100, Philip Pemberton wrote:
> Well, it looks like I won't be doing any more debugging today...
>
> My Master128 just caught fire! I had the 1MHz bus hooked up to a HP 1651B
> logic analyser so I could watch the IDE signals (and hopefully find the
> glitch in the hardware). Next thing I know, there's the sound of an
> electrical arc, and smoke billowing out of the power supply area of the
> 'Beeb!
Bah, it's no fun unless there are flames too! ;-)
> Sooo.. Does anyone in the West Yorkshire (around Leeds preferably) area have
> a spare Master 128 or a PSU for said Master that I could have (or buy for a
> very small amount), seeing as mine has converted itself into a Kentucky Fried
> PSU? The mainboard appears to be intact, but the PSU looks pretty far gone.
Hmm... I almost certainly have an unknown-condition Master PSU - I think
I have a few that came in with a load of ex-school stuff, but they're
probably seperate because they're dead rather than working. Still, if
you have PSU-fixing skills it might be better than nothing.
If nobody else can sort you out then yell at least and I'll put them
under load and see what sort of state they're in.
One of our museum guys lives in the Leeds area and just comes down every
so often; I've got a feeling he's going to be there in the next few
weeks and so could probably run a PSU up to Leeds for you then.
Bit of a wait for what might be a duff PSU that needs fixing anyway
though...
Of course scrap PC PSUs make good emergency beeb power supplies...
> I've no idea what happened - IME the PSUs will shut down if they overload,
> but the machine was still outputting video when the PSU died...
Noise supression caps on the input to switchmode PSUs are notorious for
failing, let out lots of smoke, and usually cover the board in muck. The
PSU typically carries on operating after they fail too, although
sometimes it'll take a fuse or fusable resistor with it.
Are you sure this isn't all that it is? Said caps are normally yellowish
rectangular blocks close to where the mains feed enters; I don't know
offhand if the Master PSU has them - we often have smoke incidents
involving them in other PSUs at the museum though!
Chopper transistors often go too, but they usually do so silently and
without any drama.
It's pretty typical for the voltage regulation to only be done on the
main +5V rail too (other rails just follow whatever the main rail is
doing), so it's possible something happened to one of the other PSU
rails and that it wasn't protected at all, which could have resulted in
all sorts of shorting fun...
cheers
Jules