(Topic ID: 228292)

fish tales c46 fireworks


By jgadzia

7 months ago



Topic Stats

  • 7 posts
  • 3 Pinsiders participating
  • Latest reply 7 months ago by barakandl
  • Topic is favorited by 1 Pinsider

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#1 7 months ago

my sound on my fish tales was going out and saw that c28 was blown, went in and replaced c28 plus several other capacitors that were testing bad. plugged it back in and everything worked great for the few minutes i tried it. came back a few days later and was replacing some bulbs(no sound was running) after about 15 minutes, I heard a pop and smoke coming from the back board. shut the power down and now see the C46 has gone up in a blaze of glory. c28 seems to be ok. These capacitors are both attached to U1. Is there something else I should be checking before just replacing C46?

thanks

#2 7 months ago
Quoted from jgadzia:

my sound on my fish tales was going out and saw that c28 was blown, went in and replaced c28 plus several other capacitors that were testing bad. plugged it back in and everything worked great for the few minutes i tried it. came back a few days later and was replacing some bulbs(no sound was running) after about 15 minutes, I heard a pop and smoke coming from the back board. shut the power down and now see the C46 has gone up in a blaze of glory. c28 seems to be ok. These capacitors are both attached to U1. Is there something else I should be checking before just replacing C46?
thanks

bump

#3 7 months ago

Probably just bad tantalum capacitors. I'd put in electrolytic style capacitors or at least bump up the voltage rating on a new tantalum.

If two 1uF tantalums have gone up in smoke now i wouldn't trust any of the rest of the same type/value of used on that board.

#4 7 months ago

Tantalum caps are wonderful caps but don't like two things.
Over voltage.
Reverse voltage.

The fact that it is blowing can be indicative of another problem.
What is the voltage going into cap? And what is the voltage rating of the cap?

#5 7 months ago
Quoted from G-P-E:

Tantalum caps are wonderful caps but don't like two things.
Over voltage.
Reverse voltage.
The fact that it is blowing can be indicative of another problem.
What is the voltage going into cap? And what is the voltage rating of the cap?

the tantalum caps don't age well and the 90s where a bad time for them. I watch all sorts of tech youtube videos where people diag old gear and fix it. Countless gear from the 80s and 90s is not working because of a dead shorted tantalum. Many are a 16v tantalum across a well filtered 5v rail. They cut it off and boom the computer boots up. If the power supply does not shut down from over current. Fireworks.

I have had too many tantalum explode on me. Power up a board that has been shelved for years (like a cheap squeaker). Better put goggles on.

Just bad experience makes me not like them. I imagine today's tantalums are better than the ones in the 80s and 90s... but ask me in 40 years.

Here is a cool repair video I watched the other day for a fancy Data IO burner. (dead tantalum)

#6 7 months ago

I'll have to call BS on them not aging well. We have systems pushing 40 year mark with tantalum's. If it wasn't for routine maintenance, the electrolytics would ALL be shot many times over (high ESR and/or low value due to being dried out) but the tantalum's will still be within spec. We routinely bring some of the equipment back every 8 years or so for revalidation. We now have the techs just replace all the electroltyics. In that time, we have replaced *one* tantalum (and that was due to operator head-space). Worst is when the electroltyics spew out electrolyte out the bottom and nobody notices until the damage is done.

What does cause them to age prematurely is what I listed -- they do not take kindly to over voltage or reverse voltage. In a properly designed circuit, tantalum failures are rare.

On the old board like shown in the video - we have more problems with the old carbon composition resistors than tantalums. They absorb moister over time and change value. Did you notice there were *no* electroltyic capacitors on the board shown in the video? Why do you suppose that is the case with this board? If there were, they would have ALL been replaced at least three times before the one tantalum was replaced.

And since you were speaking of power up stuff not powered on in years. It's typically not the tantalum's that are the problem (and party poppers), it's the electrolytics. For this we created a custom 'capacitor reforming' cage at work. Even bringing up the electroltyic caps slowly will cause some of them to blow... even if the caps have never been used. We use the cap reformer for unused electroltyics that have been in storage for up to about 10. Once they hit ten, in the trash they go.

#7 7 months ago
Quoted from G-P-E:

I'll have to call BS on them not aging well. We have systems pushing 40 year mark with tantalum's. If it wasn't for routine maintenance, the electrolytics would ALL be shot many times over (high ESR and/or low value due to being dried out) but the tantalum's will still be within spec. We routinely bring some of the equipment back every 8 years or so for revalidation. We now have the techs just replace all the electroltyics. In that time, we have replaced *one* tantalum (and that was due to operator head-space). Worst is when the electroltyics spew out electrolyte out the bottom and nobody notices until the damage is done.
What does cause them to age prematurely is what I listed -- they do not take kindly to over voltage or reverse voltage. In a properly designed circuit, tantalum failures are rare.
On the old board like shown in the video - we have more problems with the old carbon composition resistors than tantalums. They absorb moister over time and change value. Did you notice there were *no* electroltyic capacitors on the board shown in the video? Why do you suppose that is the case with this board? If there were, they would have ALL been replaced at least three times before the one tantalum was replaced.
And since you were speaking of power up stuff not powered on in years. It's typically not the tantalum's that are the problem (and party poppers), it's the electrolytics. For this we created a custom 'capacitor reforming' cage at work. Even bringing up the electroltyic caps slowly will cause some of them to blow... even if the caps have never been used. We use the cap reformer for unused electroltyics that have been in storage for up to about 10. Once they hit ten, in the trash they go.

i guess all the 30 year old gear i had to fix with fried tantalums was poorly designed.... yeah they used them fudging tantalum caps. =D

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