Anyone read anywhere what the failure mechanism is for solid dielectric caps of the tantalum variety ? In my experience, no matter what the value, working voltage, or format (bead, bullet or box), they always seem to fail leaky. Not open or short (well, very occasionally short). Just leaky.Example. Today, I had a Mesa Boogie combo cross my bench. Very odd problem in that when the 80Hz slider in the graphic was advanced in the 'boost' direction, the audio suddenly went very distorted, and then disappeared. There was also a slight 'scratchiness' to this pot, which did not feel like a bad or dirty track.When I got the graphic pots board out, it was actually quite a simple affair, with each of the 6 bands having just a pot, one resistor, one choke, and one cap. On the 80Hz channel, this cap was a 3u3 tantalum bullet, and it was 2k leaky. Why ? The device is under no voltage stress at all in this position, being subject to low signal levels only. I wonder if it's some kind of internal 'growth' like the dreaded tin whiskers, which causes it ?A new cap (used a 3u3 tant bead that I had in stock) restored normal operation of the equaliser, and all scratchiness in that band disappeared.Arfa

Tantalums have kind of a bad reputation for shorting, and that's been my experience. Not really seen them leaky or open.The scratchy sound of the pot is typical of DC leakage in such a circuit. Can make a volume pot or similar sound "dirty" or make woofers go "whoomp" when the control is moved.But then you know this, yes? I know you have loads of experience with this stuff.I got the "whoomp - whoomp" in a Yamaha receiver the other day - a bad muting transistor put DC on the volume control.Mark Z.

Tants. So what's the failure mechanism ... ?

Mar 19, 2010 26 Replies

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Sjouke Burry 16 years ago

Grant wrote: cut

Thats not the wrong side, thats the bottom side ......

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Arfa Daily 16 years ago

Oh dear ! That's right as in not left ... d;-}

Arfa

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Arfa Daily 16 years ago

Indeed it would ...

Very interesting

Arfa

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ian field 16 years ago

Who's left?

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Arfa Daily 16 years ago

Someone said that Elvis had left the building ...

Arfa

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Baron 16 years ago

Sjouke Burry Inscribed thus:

I belive I must agree ! ;-)

Best Regards: Baron.

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Franc Zabkar 16 years ago

On Sun, 21 Mar 2010 09:01:00 +1100, Grant put finger to keyboard and composed:

It was in a video mixer board. I can't remember its exact function, but it was somewhere in the signal path. The board had analogue and TTL components, so the voltages were +5V, +12V, and -12V, IIRC.

- Franc Zabkar

Please remove one 'i' from my address when replying by email.

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