Date   : Tue, 11 Aug 2009 09:42:11 +0100
From   : robert@... (Rob)
Subject: Tales of woe and stupidity

I used to build little electronic kits as a kid.. I had one that
flashed a pair of lamps off and on alternately: some capacitor driven
circuit feeding a pair of transistors to do it.

I thought this is a bit weedy, I want BIG lights...  I wasn't foolish
enough to try and switch mains through it, instead opting to drive a
relay instead of the lamps, which could in turn switch the mains
lamps.

Now the only relays I had were some hulking great things that may or
may not have been ex-GPO... I connected them up, left the mains off
for the moment while I checked they switched, and powered up the
circuit.

Click.. click  click... BANG, BANG....

Both transistors blew up!  Bits of plastic flew off across the room...
 On reflection, I guessed that these big hulking relays probably drew
a little more current than the cheap transistors in this kit were
designed to switch ...


Another one I was involved with picking up the pieces of, although I
hasten to add I was not responsible for:

At work, we supplied a multi-user accounts system that used dumb
terminals.  (we're still talking P1 era here.)  A cheap way of getting
nice colour terminal was to use a low-spec PC running a terminal
software - it was small enough to run from floppy, so we'd
occasionally re-use an old machine or old motherboard with just a
floppy drive to make up a cheap terminal.  In this case, it was an old
486 board in a new case. Now this board, to keep it's BIOS, had a
plug-in battery pack, much like the Master 128, rather than the
on-board coin cells you saw later.  It looked like it was just an AA
battery encased in a plastic box.

It had been in the customers less than a week, when we got a telephone
call: "The computer has blown up".  Yeah, LOL, silly customers, it's
just stopped working..

I pop along ... the computer was under the desk, by the girls feet..
all the buttons off the front were on the floor, as was the front of
the floppy drive and the spare drive bay covers.  Hmm..  I pull it out
from under the desk.  The back of the case, where all the expansion
ports were, was bowed outwards....

Yup... something was definitely wrong,  I thought at this point I'd
better take it back to the office rather than investigate further.

Once in the workshop we took the lid off.   As you may have guessed by
now, the battery had exploded...  Bits of plastic had made their way
/through/ the ribbon cables, there was battery acid everywhere, and
nothing remained that was big enough to identify as part of the
battery itself.

The whole thing was a write off.  We managed to re-use the case and
the power supply, although both had been corroded internally.
Everything else in the machine was ruined.

So yes, I think they were right when they said it had "blown up".  The
poor girl whose feet it had been beside must have been scared out of
her wits.. And we never laughed again when a customer said that to us
...