Date   : Mon, 22 Jan 2007 22:25:12 -0000
From   : BBCMailingList@... (Ian Wolstenholme)
Subject: Narrow Escape...

Thanks to everyone who has replied.  I wonder if I may
have been lucky.  Although there was a fizz then a
pop, which I'm about 97% sure was at the host
adapter end and 95% sure was the capacitor next to
the 0V and 5V inputs, there wasn't any smoke on this
occasion and I can't see any damage to the board at
all.

The Master 128 has survived, the 1 MHz Bus is still
working as far as I can make out and the aux. power
(which I was using to power the board) is still giving
12V (actually 11.97V to be exact) and 5V (5.12V to
be exact).

I pride myself on being one of the fastest on/off
switchers in the West (well North-West!).  Whenever
I connect anything to anything, I keep the fingers on
the on/off switch for at least 30 seconds and at the
first sign of anything going wrong, off it goes!  So my
fast reflexes may have saved the day!

I'll try getting hold of a replacement capacitor and see
if that works, otherwise it looks like it might have to
be a wholesale replacement of ICs.

Best wishes,



Ian


----- Original Message -----
From: Jules Richardson [mailto:julesrichardsonuk@...]
To: bbc-micro@...
Sent: Mon, 22 Jan 2007 13:46:49 -0600
Subject: Re: [BBC-Micro] Narrow Escape...

Sprow wrote:
> As a general rule, the most expensive hard to find part will be damaged
> first and in a case bulging way, followed by the hard to desolder parts,
> then the fuse goes last,

"The electronics exist to protect the fuse" :-)

re. tantalum capacitors, I don't think I've ever had one short on me. Several 
have gone bang very loudly and released lots of smoke (fun on machines with 
big exhaust fans!) but I've never had one go dead short. I'm sure it 
happens... but just not always.

Looking at a photo of the board, it's 15 chips and they're all common enough 
TTL logic (there's one F-series part in there, the rest is LS). I'd suggest 
raiding some old scrap for donor chips (preferably socketed ones to save on 
the desoldering!) then get the side cutters out and remove all the 
possibly-dead chips from the Akhter board. Desolder the legs left in the PCB 
from the chip removal, clean the board up, solder the replacements in and it 
should be good to go.

cheers

Jules


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