Bloody Tantalums

[Ray]

Just spent many hours today pinpointing a faulty tantalum capacitor.

It was in the display board of the SC Deep Cycle battery charger.

The charger would run for about 5 minutes, then slowly the 5V rail to
the PIC would slowly drop to 3.5V or so and everything would stop,
obviously.

If they used a simple 7805 regulator, without a series input resistor,
the blue smoke would have been released and made the fault finding far
easier

In this instance, obviously (now) the cap began leaking more the longer
volts were applied.

Ray

 

[Jonno]

Just spent many hours today pinpointing a faulty tantalum capacitor.

It was in the display board of the SC Deep Cycle battery charger.

The charger would run for about 5 minutes, then slowly the 5V rail to
the PIC would slowly drop to 3.5V or so and everything would stop,
obviously.

If they used a simple 7805 regulator, without a series input resistor,
the blue smoke would have been released and made the fault finding far
easier

In this instance, obviously (now) the cap began leaking more the longer
volts were applied.

Ray

Yeah a lot of companies have stopped using the blue smoke indicator.
It takes a smarter more educated fellow to find them. Well done.
Can you charge extra for frustration?

 

[Phil Allison]

"Ray"

Just spent many hours today pinpointing a faulty tantalum capacitor.

It was in the display board of the SC Deep Cycle battery charger.

The charger would run for about 5 minutes, then slowly the 5V rail to
the PIC would slowly drop to 3.5V or so and everything would stop,
obviously.

If they used a simple 7805 regulator, without a series input resistor,
the blue smoke would have been released and made the fault finding far
easier

In this instance, obviously (now) the cap began leaking more the longer
volts were applied.

** LOL !

Most experienced service techs have the same attitude towards any bead
tantalum cap they see


* SHOOT FIRST * - ask questions later ......




....... Phil

 

[Bob Parker]

** LOL !

Most experienced service techs have the same attitude towards any bead
tantalum cap they see


* SHOOT FIRST * - ask questions later ......




...... Phil

It ain't only the bead ones .... the axial ones do it too.

Bob

 

[kreed]

Just spent many hours today pinpointing a faulty tantalum capacitor.

It was in the display board of the SC Deep Cycle battery charger.

The charger would run for about 5 minutes, then slowly the 5V rail to
the PIC would slowly drop to 3.5V or so and everything would stop,
obviously.

If they used a simple 7805 regulator, without a series input resistor,
the blue smoke would have been released and made the fault finding far
easier

In this instance, obviously (now) the cap began leaking more the longer
volts were applied.

Ray

When I see those rotten bloody things, I replace them with an
electrolytic.

Seen too many of them short internally, and in the 1980's actually saw
one catch fire right before my eyes !

 

[Bob Parker]

When I see those rotten bloody things, I replace them with an
electrolytic.

Seen too many of them short internally, and in the 1980's actually saw
one catch fire right before my eyes !

The old STC 151 VHF transceivers used to have bead tantalums in the
PA stage. If it was mistuned, it was common to see just two bits of wire
sticking out of the board where each cap used to be ... they exploded!

 

[Phil Allison]

"Bob Parker"

The old STC 151 VHF transceivers used to have bead tantalums in the PA
stage. If it was mistuned, it was common to see just two bits of wire
sticking out of the board where each cap used to be ... they exploded!

** He, he - seen more than a few charred, black " peas " roll out of
odd pieces of gear when I tipped them up in my time !!




........ Phil

 

[Jonno]

The old STC 151 VHF transceivers used to have bead tantalums in the
PA stage. If it was mistuned, it was common to see just two bits of wire
sticking out of the board where each cap used to be ... they exploded!

Funny. They must have been used in the wrong types of situations.
The last Philips transmitters they designed were full of them, and yet
they performed OK. (in most cases)

 

[Bob Parker]

Funny. They must have been used in the wrong types of situations.
The last Philips transmitters they designed were full of them, and yet
they performed OK. (in most cases)

Hopefully the Philips ones didn't put a lot of RF current through
them, and used more appropriate caps for high frequency supply
bypassing? (Guessing a bit here - it was over 30 years ago!)

 

[Tsunami Australia]

Funny. They must have been used in the wrong types of situations.
The last Philips transmitters they designed were full of them, and yet
they performed OK. (in most cases)

Um the Philips transmitters are starting to have issues with them.
Look at the PRM80 series radios. There's a good number of them gone
ferral now...started with tant issues.

 

[Franc Zabkar]

When I see those rotten bloody things, I replace them with an
electrolytic.

Seen too many of them short internally, and in the 1980's actually saw
one catch fire right before my eyes !

Same here. I must have replaced hundreds of faulty tantalums during
the same period.

- Franc Zabkar

 

[budgie]

Um the Philips transmitters are starting to have issues with them.
Look at the PRM80 series radios. There's a good number of them gone
ferral now...started with tant issues.

Nope, that's all surface-mount aluminium electros .....

 

[Ross Herbert]

It ain't only the bead ones .... the axial ones do it too.

Bob, are you referring to types such as Kemet hermetically sealed
tantalums? Heaps of these used in mil spec equipment so I would be
surprised if they failed very often at all. The secret to using tants
to to use them only in a well regulated environment where they are not
subject to voltage spikes. They do have extremely low ESR and long
life. I use Kemet hermetics around my linear voltage reg circuits
along with standard aluminium electro's in the appropriate places
without any failures in many years of service. I would agree with the
adage "never to use tantalums" as long as it applied only to the solid
dipped type.

 

[Bob Parker]

Bob, are you referring to types such as Kemet hermetically sealed
tantalums? Heaps of these used in mil spec equipment so I would be
surprised if they failed very often at all. The secret to using tants
to to use them only in a well regulated environment where they are not
subject to voltage spikes. They do have extremely low ESR and long
life. I use Kemet hermetics around my linear voltage reg circuits
along with standard aluminium electro's in the appropriate places
without any failures in many years of service. I would agree with the
adage "never to use tantalums" as long as it applied only to the solid
dipped type.

I'm thinking right back to some professional Italian
telecommunications gear manufactured in the late 60s I used to work on.
I don't remember the brand of the caps. The technology's probably
changed heaps since then. Apologies for leaving out those 'small' details.

Bob

 

[Ross Herbert]

I'm thinking right back to some professional Italian
telecommunications gear manufactured in the late 60s I used to work on.
I don't remember the brand of the caps. The technology's probably
changed heaps since then. Apologies for leaving out those 'small' details.

Bob

If they were stainless steel cases with glass seal then they were
probably hermetic tantalums.

I will post a pic on abse of a small dual rail 317/337 based linear
mains supply pcb I designed showing where I use the Kemets.

 

[Tsunami Australia]

Nope, that's all surface-mount aluminium electros .....

Depends which model. There was a series with tants. There were 2
series of the PRM80.

 

[budgie]

Depends which model. There was a series with tants. There were 2
series of the PRM80.

I'll have to take your word for that. Every PRM80 I've seen (literally dozens)
had those @#$%& SMT aluminium electros. Where's Jason when you need him?

 

[Franc Zabkar]

It ain't only the bead ones .... the axial ones do it too.

Bob

I can confirm that. I've seen such failures in Control Data BK7 series
disc drives.

- Franc Zabkar