Tantalum fumes

gmphadte · 20th October 2006, 07:37 AM

This has been happening to power supply bypass tantalums near an IC (LH0002)on one pcb. This is not audio stuff but an EchoSounder. The 10 ohms resistor in series with this 10 mcf tantalum becomes hot, and the cap tends to fume. Remove the caps on both (+/_)rails and there is no functional problem.
The ES has been idle for some months, not powered.
Change the caps to new, same problem. Bypass these caps with another electrolytic, same problem.
I am sure many of u know why it happens.
The PSU is an SMPS with 24Vdc input.

Can anybody explain why?

Gajanan Phadte

Elvee · 20th October 2006, 09:19 AM

Hi,

1) Check voltage and polarity. The real ones, not the supposed voltage, or the polarity silkscreened on the PCB.
2) Check that at no moment during the power-up or down sequence the voltage becomes reversed. If it does, place a schottky protection diode across (1N5820 f.e.)
3) Occasionally, tantalum can be damaged by a current surge, but with 10ohm in series, it's unlikely.
LV

traderbam · 20th October 2006, 11:22 AM

The only other possibility is a problem with the SMPS causing HF to be fed through the tants. Unlikely, but if all else seems ok...

20th October 2006, 07:37 AM	#1
gmphadte diyAudio Member Join Date: Jul 2003 Location: Dona paula, Goa	Tantalum fumes This has been happening to power supply bypass tantalums near an IC (LH0002)on one pcb. This is not audio stuff but an EchoSounder. The 10 ohms resistor in series with this 10 mcf tantalum becomes hot, and the cap tends to fume. Remove the caps on both (+/_)rails and there is no functional problem. The ES has been idle for some months, not powered. Change the caps to new, same problem. Bypass these caps with another electrolytic, same problem. I am sure many of u know why it happens. The PSU is an SMPS with 24Vdc input. Can anybody explain why? Gajanan Phadte

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20th October 2006, 09:19 AM	#2
Elvee diyAudio Member Join Date: Sep 2006	Hi, 1) Check voltage and polarity. The real ones, not the supposed voltage, or the polarity silkscreened on the PCB. 2) Check that at no moment during the power-up or down sequence the voltage becomes reversed. If it does, place a schottky protection diode across (1N5820 f.e.) 3) Occasionally, tantalum can be damaged by a current surge, but with 10ohm in series, it's unlikely. LV

20th October 2006, 11:22 AM	#3
traderbam diyAudio Member Join Date: Jan 2002 Location: Earth	The only other possibility is a problem with the SMPS causing HF to be fed through the tants. Unlikely, but if all else seems ok...

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