Caps loadly popping on motherboard

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I've got a motherboard that runs off a single 12V supply (Via ITX board). It
provides power to the hdd and cd-rom via a power out plug. I hooked it up
today with a 12V supply and shortly after starting it up one of the caps in
the onboard power supply popped quite loudly. Then a minute or so later
another one popped. I was only running a single hdd and no CD rom so
wouldn't have thought I was overpowering it. Can anyone tell me what is
likely to have happened?

Thanks,
Michael



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You'd think I would have learnt how to spell loud by now :-)

Michael



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**It wasn't really a 12 Volt supply?

Did you measure the "12 Volt supply"?

Trevor Wilson



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Polarity?



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**Good point, though I doubt anyone could be THAT stupid.

Trevor Wilson



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  So this is an offer to better that?  I'll bite. :-)

  A small "Squirrel" printer used in POS applications come in for repair.
Report said "Dead".  Apon closer inspection and preparation to apply 12v to
power up the unit, we notice the PCB is completely cooked.  Nothing that a
mere 12v could do, this needed more juice than that.  Turns out client lost
the adaptor for one of these things, and made up their own - by plugging it
into the mains.
--
Linux Registered User # 302622
<http://counter.li.org

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**That's pretty good. I have photos (somewhere) of a turntable, where the
client accidentally wired the phono leads to the mains supply......

The headshell was one of those plastic ones and arrived as a blob on the end
of the tone arm. It was a beaut. The other one (which I also have photos of)
is where a client's wife/girlfriend arrived home early, to find my client in
bed with another woman. She grabbed a hammer and took to his hi fi system.

Hell hath no fury and all that.

I'll try to locate the pics, scan and post them somewhere.

Trevor Wilson



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Best one I heard was a friends sister was using a handheld cake mixer
when the mains lead somehow worked loose and fell into the cake mix.
Without thinking she picked up the leads and licked the cake mix of them
and got one hell of a boot on her tongue.

Dorf


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A million years ago, or thereabouts, I bought a single-board computer,
called AIM65. Based on a 6502 chip. It needed a power supply that provided,
I think, +5, and +24 volts. I was dead tired, and it was about 1:00AM, and I
was wiring and soldering a breadboard rat's nest of a temporary power supply
, sitting on the floor. I fired up the finished supply, and it didn't work.
I bent over it to look at what was wrong, and a big electrolytic (about the
size of a D cell) exploded and shot past my head and made a big dent in the
ceiling which is still there. It could have blinded me. I had wired it back
to front.
Yes, some of us are THAT stupid. Sometimes.



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Sometime back another young poster to this NG had a similar experience with
an exploding electrolytic.
Difference was it hit him square in the forehead, leaving a crosshair
pattern resembling the vent release on the top of the cap.
Lucky he didn't cop it in an eye !

Cheers,
Alan





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     I installed a 10uF electrolytic backwards in an amp I was repairing
once. It was a bypass cap on an STK package.
     There was a very loud bang as I was leaning over the unit, and the
cap's can flew past my face, missing my eye by maybe an inch before
hitting the ceiling then bouncing around the room.
     Nice to know I'm not the only one's who done that. :)

Bob

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A looooong time ago I used to work on welding machines
at a manufacturer, and hooked up the enormous ~20 x 10cm dia.
Mallory can electrolytic used on the rectified output of the
DC MIG welding output section backwards...

The sides were open on the machine in production,
luckily I was standing just behind the rear plate when I
powered it up (415V 3 phase too)...
The cap blew like a grenade, exploding its guts everywhere
with a bang and force that scared the absolute shit out of
me and everyone else in the factory.

Took me a while to clean up the inside of that machine and
all around :)

Since then and a smaller occasion (not backwards cap)
I always wear safety glasses when powering up a suspicious
or repaired power supply or other device with electro's
and high current supply, don't want to lose an eye either...
My safety glasses sit on the shelf just above the workbench.
I've had tantalum caps throw burning shards around too.


--
Cheers,

Marc

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Better, many years ago Compaq 386 motherboards used very similar
connectors for the system fan and lithium battery, I felt the
compression from the explosion about 15 yards away.
--
Clint Sharp

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Workshop, big solid-state P.A. amplifier....senior of technicians and
part-owner of business replaced BIG supply electros - a little casually
!  On turn-on it went REALLY bang, the long strips of paper/aluminium
foil tangled in the overhead ceiling fan - hilarious after the shock
subsided.

The electrolyte mist most corrosive on pretty brushed-aluminium front
panels etc., of other customer equipment....more care taken afterwards
with double-checking of polarity !

Reckon it might have been one of the YAMAHA P-2200 series from 20+ years
ago.

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Can't say I've ever accidentally exploded and decent sized electrolytics,
although I have managed to put a few smaller caps in circuit arse about. One
thing that does come to mind however re. exploding caps, is when i was at
TAFE and some bright spark decided to drop an electrolytic cap in the solder
pot. Luckily it was close to lunch time and everyone had left the room
before the cap went bang and showered the room with molten solder.

James



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in the very early 1980's I recall doing the occasional repair jobs for
a bloke (now retired 16 years back) who amongst other things, had a
quantity of coin-operated video games in bars and shops.  One day I
remember having to service a game called "asteroids" that had a
"vectorbeam" or "XY" monitor (For those unfamiliar with this long
forgotten? technology - there isnt any raster scan, the deflection
coils are driven directly by amplifiers that are driven via 2 separate
D/A converters on the logic board, kind of like a CRO.

After a bit of stuffing around, we discovered that he had a spare
logic board of the same game, but made by a different manufacturer, so
we decided to try it.  All was not well, the CPU was running and we
could see the game on the monitor, but the picture was shaking like
mad in both directions.  Just as I was sticking my head in the back of
the machine to try and diagnose the fault, there was an almighty
"BANG" like a gunshot, followed by a second "BANG" a few seconds
later.  Both were so loud our ears were ringing and sore for the next
hour or so.

Turned out the logic board had an onboard power supply providing +/-
12v for the D/A converters, and the AC was fed directly from a power
transformer to the board.  Only problem was that one board had 4700uf
16v caps on it, and the other had 25v caps on it, and one cabinet had
a much lower secondary voltage coming from its transformer than the
other.

when swapped - BANG !

I learned a very important lesson about the dangers of electrolytics
that day, fortunately havent had a repeat.



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Yes, well... We can all be stupid at times. Recently I had to cut the output
wires of an *AC* plugpack. Then I spent a fruitless couple of hours trying
to determine what polarity was each lead...
<g>



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So did you get it right in the end?

Dorf

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Yes, I managed to identify the polarity in a 50th of a second, although it
changed immediately afterwards, but it's OK because it changed back again...



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