486 board covered in tantalum capacitors

[cmc]

I bought two 486 boards recently, a DTK PKM-0038s and a PKM-0037s. The 0038s has been great and is in a build now (details in a different post).

I'm rather worried about the 0037s. It is covered in tantalums. I have heard that those are likely to fail in an explosive way after 20+ years. The good news is that the board does boot now and actually works well. An ohmmeter check on each did not reveal anything suspicious.

Nevertheless, any recommendations on replacing them? It seems like it would be big undertaking. How necessary is it given no current evidence of a problem?

Pictures:

 

[DonutKing]

If everything is working fine now I would just leave them.

When they fail, they make a big noise but that's about it. I've had a few boards with tantalum caps blow. Once the caps are replaced everything works fine again.

 

[SomeGuy]

They won't usually damage the motherboard. You'll just need to brush off some carbon and a few little yellow bits.

It's likely re-soldering would actually do more damage. Those buggers are usually attached to thick ground planes that are difficult to heat up.

But if you have a bare board out on a workbench that you haven't powered up in 10 years - you might want to duck when you first turn it on.

 

[luvit]

...that board has *tantalums*! Tantalums can explode and/or short over time which is even worse than a failed electrolytic. Shorting damage from a bad tantalum can take out hard-to-replace ICs...

ok, guys... so i see a lot of statements like this quote on the forum:
i was considering recapping my 5150 & 5160 before i got too involved with them.. i don't WANT to recap a board if i can just replace them as they blow.
this includes motherboards and power supplies... am i misunderstanding something??

 

[Stone]

Jeez... talk about alarmists!

 

[smeezekitty]

Honestly I think the problem prone ones were earlier on like 1980s boards. I have had two 486 boards with those so far and none blown

 

[Chuck(G)]

Aluminum electrolytic caps are far more likely to cause issues than are aging tantalums. I've never seen a tantalum blow and take a component along. Just some noise to be ignored, most of the time.

 

[NeXT]

When tantalums blow I just clip off the remains and keep on chugging. I've had hard drivee formatting on the bench when they smoke up a tant. It's always a pretty show.

 

[Dwight Elvey]

Surface mount Tantalums can do some damage.
The epoxy ones just make a lot of smoke and short.
Often with a strong supply they just blow open.
I've seen serious damage from the little square
surface mount ones. There is no real age rule that goes
with them. I've seen them fail after 1 year and some
tantalums in my oldest computer that have been
working fine now for 43 years.
I would never think of replacing them with electrolytics.
They do not provide the same bypass capabilities without shunting
them with large ceramics.
Dwight

 

[Chuck(G)]

I don't think anyone was suggesting replacing tants with electrolytics, Dwight. Fortunately, there are some more alternatives. If you're replacing a SMD tantalum, for modest capacitance (22-47 uF), there are stacked MLCCs (a bit expensive). For larger values, I wonder about the characteristics of sold-polymer electrolytic caps might suit many applications.

 

[cr1901]

I would never think of replacing them with electrolytics.
They do not provide the same bypass capabilities without shunting
them with large ceramics.
Dwight

I've done that just fine with an ISA card with bad tantalums (shorting 12V to GND). It's been 13 months since I did that repair and the card still works fine. And technically, aren't tantalums a type of electrolytic capacitor anyway?

 

[Dwight Elvey]

Yes technically they are but when most people refer to electrolytic,
they refer to aluminum electrolytic.
Tantalums get their higher capacitance and better frequency response
at high frequencies by having thinner oxide layers. This means a small
flaw is more likely to cause a failures as well. Since they are a dry
electrolyte, they don't suffer from gradual increased ESR and reduced
capacitance.
Dwight

 

[cmc]

Thanks everyone for the replies. I will forgo any replacements until one breaks -- should be an interesting post if one does!