From: Alan Pearce <kiwiantipodean@googlemail.com>
To: Microcontroller discussion list - Public. <piclist@mit.edu>
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Date: Fri, 22 May 2020 18:48:09 -0700
Subject: Re: [EE] Light bulb moment (literally)
Thread-Topic: [EE] Light bulb moment (literally)
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I had a case where a multilayer ceramic cap on a memory board in a
minicomputer decided it preferred life as a resistor. The system had a
card cage for some considerable number of cards and only had a CPU,
Memory, serial I/O, disk interface and tape interface. so the 5v 300A
switch mode power supply was pretty lightly loaded. When the cap went
resisitive the power supply just kept supplying current without
falling over. I got a panic call about smoke coming from the machine.
Fortunately whoever found it happening knew where the power switch was
and killed the power to the cabinet. The result was a burn in the
memory board about an inch and a half diameter with destroyed tracks
and only the glass fibers left in that area. For a number of reasons
it was decided to repair the PCB with some epoxy and patch wires for
the connections. The board then proceeded to do many years sterling
service.

On another occasion a colleague transported a PDP11/36 in the back of
a van. It was sitting on a 2 inch thick slab of foam rubber, but
unfortunately that pushed the very flimsy bottom cover onto the wire
wrap pins, impaling some of the wiring across bus and power pins.
Apparently there was a spectacular series of ping sounds as the bus
transceiver chips gave up the unequal struggle of having +/-12V
applied to the bus pins, leaving craters in the tops of the chips. Que
a trawl of the local electronics shops in a small town for as many
chips as they could find to replace them ...

On Fri, 22 May 2020 at 19:51, David C Brown <dcb.home@gmail.com> wrote:
>
> I once had a desperate phone call from the operator of our special purpos=
e
> computer that bangs and smoke were coming out of the machine.
> Turned out that a lot of tantalums had been put in the wrong way round. a=
nd
> were dying noisily.
>
> __________________________________________
> David C Brown
> 43 Bings Road
> Whaley Bridge
> High Peak                           Phone: 01663 733236
> Derbyshire                eMail: dcb.home@gmail.com
> SK23 7ND          web: www.bings-knowle.co.uk/dcb
> <http://www.jb.man.ac.uk/~dcb>
>
>
>
> *Sent from my etch-a-sketch*
>
>
> On Fri, 22 May 2020 at 16:40, mike brown <mike@n5qmg.com> wrote:
>
> > I built a prop for an escape room and had to use one of these dynamos t=
o
> > power the circuit when the player pedalled a bicycle.  It generated wel=
l
> > over 36V when pedalled hard.  You should have heard the tantalum capaci=
tor
> > explode in testing.  Sounded like a rifle going off.
> >
> > On Fri, May 22, 2020, 10:29 David VanHorn <microbrix@gmail.com> wrote:
> >
> > > My first bike had a combination bulb and fluorescent light.  6: tube.=
 The
> > > generator had the usual 6V output for the bulb and 100V for the tube.
> > > Never seen one like that since.  This was around 1967 or 68
> > >
> > >
> > > On Fri, May 22, 2020 at 9:19 AM Chris McSweeny <cpmcsweeny@gmail.com>
> > > wrote:
> > >
> > > > It is, except that the maximum voltage is speed dependent. It is
> > (was?) a
> > > > common modification to use one to supply 12V across two lights in
> > series,
> > > > but with a switch to short out one of the lights at lower speeds wh=
ere
> > > the
> > > > dynamo can't supply 12V.
> > > >
> > > > On Fri, May 22, 2020 at 9:34 AM David C Brown <dcb.home@gmail.com>
> > > wrote:
> > > >
> > > > > I have just realised that the traditional "dynamo" used for bicyc=
le
> > > > > lighting (and which is really) a magneto) is, despite being sold =
as
> > a 6
> > > > > volt machine,  a actually a constant current device.
> > > > > Since both voltage and frequency - hence reactance - rise
> > > > > approximately linearly with speed the current remains constant.
> > > > > __________________________________________
> > > > > David C Brown
> > > > > 43 Bings Road
> > > > > Whaley Bridge
> > > > > High Peak                           Phone: 01663 733236
> > > > > Derbyshire                eMail: dcb.home@gmail.com
> > > > > SK23 7ND          web: www.bings-knowle.co.uk/dcb
> > > > > <http://www.jb.man.ac.uk/~dcb>
> > > > >
> > > > >
> > > > >
> > > > > *Sent from my etch-a-sketch*
> > > > > --
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