Exploding Capacitors

Can voltage that is too low or transient spikes cause a capacitor to explode? I'm not talking about capacitors that have dried out or are not properly connected.

I blew a capacitor on a game board I'm trying to get working and the only culprits I can think of are the transformer assembly or the sub- power assembly called the Regulator/Audio PCB, which does some audio amplification, and some voltage regulation.

I'm still searching for technical information on how to test these components, and if I can find out why the cap blew, perhaps it will lead me to figuring out what I can't get the game to work.

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Thanks.

Darren Harris Staten Island, New York.

Reply to
Searcher7
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Can voltage that is too low or transient spikes cause a capacitor to explode? I'm not talking about capacitors that have dried out or are not properly connected.

I blew a capacitor on a game board I'm trying to get working and the only culprits I can think of are the transformer assembly or the sub- power assembly called the Regulator/Audio PCB, which does some audio amplification, and some voltage regulation.

I'm still searching for technical information on how to test these components, and if I can find out why the cap blew, perhaps it will lead me to figuring out what I can't get the game to work.

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Thanks.

Darren Harris Staten Island, New York.

I ancient times, circa (when I was a young tech) it happened quite often. In modern times I have only seen an "explosion" rarely and ones that were done on purpose by angelic students. A malfunction that would cause AC across an electrolytic could do this. Reverse polarity or serious over-voltage, maybe.

Tom

Reply to
Tom Biasi

What kind of capacitors? Generally capacitors won't explode, so you have to do something significant. Like a really big spike.

Or put a tantalum capacitor in backwards, and it will explode. I can't remember for average electrolytics, it's been a while since I put one in backwards

Michael

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Reply to
Michael Black

Tantalums will certainly explode and they don't have to be put in backwards to let loose. They should never be operated at more than 50% of their rated capacity. Other types can explode, too. Capacitors store energy and can let it loose quickly. That's what they do.

Reply to
krw

ve

Well the game board used to work. I have a second board that I don't want to take chances with and plug in until I know what happened.

The info on the capacitor which is in the same place as the exploding one on the other board is as follows:

"ITT / 130.OU / 35.0S"

It would be the little black cap in between the +15V and +22V test points in this picture:

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iMillipedePCB.jpg

When the cap blew I was testing the Regulator/Audio PCB, which was measuring ok where it puts out -5VDC:

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(All voltages on the AR PCB were tested within 2V of spec).

Right now I'm searching ofor info to see it the transformer could be the culprit:

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Thanks.

Darren Harris Staten Island, New York.

Reply to
Searcher7

"Searcher7"

** There are many reasons why an aluminium electro might explode:
  1. DC voltage in excess of rating applied.

  1. Reverse DC voltage applied.

  2. The cap had become de-polarised ( eg through old age) and lost voltage rating.

  1. Internal short in cap.

In all cases, energy from the power supply heats the electrolyte inside the cap to boiling point and the pressure build up causes it to eventually explode.

At the time of explosion, vapour will be emitted and a rather nasty smell.

Your case sounds like #3.

.... Phil

Reply to
Phil Allison

I am going to guess you have the 1977 version of "MILLIPEDE". The following seem to pertain to the 1982 version.

Here is a service manual

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And a board for sale.

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Make note of the statement about this model having power supply problems.

Here is a schematic

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On the schematic page 6 bottom left hand corner is C39 100uF 35V going to the input of VR1 a 7815 regulator. With 22 VDC on a 35 volt capacitor it should be safe. When electrolytics dry out the ESR goes up which would exacerbate a heating problem.

Being the parts are 35 years old they could have dried out and failed. That is why they have replacement parts.

Did you acquire it with the failed part or did it die on you? Good luck.

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Reply to
Herman

  1. Excessive ripple current through the cap - usually due to faulty choice of a cap that can't handle the ripple current.
  2. Aging cap has increased resistance and decreased ripple current handling.
  3. Excessively hot environment.

Sometimes they vent steam, often with liquid leakage, without exploding.

Likely true.

--
 - Don Klipstein (don@donklipstein.com)
Reply to
Don Klipstein

owing

/Millipede.pdf

IRCUIT-BOARD-PCB-...

ipede-sp.pdf

it

=A0That

k.

There are three of those type of caps on the Millipede PCB. And yes the board is from 1982.

I made an error in reading the info off the cap thanks to the dust, but the info is as follows: "ITT" "100.OU" "35.OS" "A x" "-40=9585=B0 C" (I'm just not sure if the O's are really zeroes).

On my spare Millipede PCB it is the cap on the right:

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ipedePCBCapacitor.jpg

On another test point at just before the cap exploded I got a reading of +24.94V. Was almost 3V over spec too high? (Perhaps that voltage in combination with it being an old cap cause it to explode).

And should I replace the chipped regular in that image?

(I really have to learn how to read schematics).

Thanks a lot.

Darren Harris Staten Island, New York.

Reply to
Searcher7

yep that transistor with a crack in it looks very suspect maybe cap dried out low resistance over heated transistor, transistor shorts full voltage to cap (boom).

There are three of those type of caps on the Millipede PCB. And yes the board is from 1982.

I made an error in reading the info off the cap thanks to the dust, but the info is as follows: "ITT" "100.OU" "35.OS" "A x" "-40?85° C" (I'm just not sure if the O's are really zeroes).

On my spare Millipede PCB it is the cap on the right:

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On another test point at just before the cap exploded I got a reading of +24.94V. Was almost 3V over spec too high? (Perhaps that voltage in combination with it being an old cap cause it to explode).

And should I replace the chipped regular in that image?

(I really have to learn how to read schematics).

Thanks a lot.

Darren Harris Staten Island, New York.

Reply to
keithdisco

tantalum capacitors can explode from spikes.

electrolytics can lose their polarisation and explode if used after being left unused for several years, or sometimes it sesm that they just explode spontaneously.

the dead part looks it it was a decoupling cap for the

7815 and the transistor opposite it. A 7815 is going to have aout 20 to 30V on it's input

If that's a date code on the black capacitor this game was assembled around 1982 and may have been unused for several decades.

--
?? 100% natural
Reply to
Jasen Betts

Thanks everyone.

I guess that on all the game boards I have that are not working I should just replace all the capacitors. The boards on average are about 30 years old.

Darren Harris Staten Island, New York.

Reply to
Searcher7

Electrolytics, yes definitely. Ceramics and mica caps, not so much; paper would be a judgement call, but it shouldn't cost an arm and a leg to replace them with polyester or polypropylene.

Have Fun! Rich

Reply to
Rich Grise

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