Tiido wrote on 2024-04-06, 10:21:

I have been trying to find info about this loss of polarity in tantalum over time and my search yields nothing, I'm most curious about it...
But what I did find is that there are filaments growing inside tantalums which can result in catastrophic failures, although in many cases they break down without damage according to a NASA study about failure modes in some types of tantalum capacitors.

I dont understand it myself its only from what I have read from anecdotes around the net, whether they are true or not I dont know, I guess an electrical engineer would be able to explain it better. Perhaps its less of a loss and more it gets shorted internally perhaps by said filaments that allows current to flow in a reverse direction which causes an explosive failure. We call it forgetting as a way for laymen to understand a complex failure mode, I do know for certain that Tantalums dont like reverse current in the slightest.

Trashbytes wrote on 2024-04-05, 09:21:

zuldan wrote on 2024-04-05, 09:05:

The Crystal chip has been ordered. Should I be replacing all the 10uF 16V Tantalum Capacitors on the board? There are 16 of them. Only 1 has a short.

If they check out ok and didn't pop the first time it powered up I wouldn't change them, but others here may have more experience with tantrum caps.

While I don't think I am a believer in the "recap everything" cult, the failure of Tantalum Capacitors is a general problem, not due to single faulty components. Most of the time, we see exploding caps rated for 16V on the +12V rail. If one tantalum blew on a system on power-up, I would recommend to swap all capacitors connected to the same voltage level, in that case, all tantalums that are on the +12V rail or the -12V rail.

As a personal, probably non-representative anecdote, I powered up a Compaq ProSignia server that was ~20 years in storage, and a tantalum on the mainboard popped. I desoldered that one, and tried it again, just to have the next tantalum pop after some more seconds of operation. After the second blown cap, I continued tests with the system outdoors, connected through an extension cord, so the smell stays outside. All three tantalum capacitors connected to +12V and finally the tantalum capacitor connected to -12V popped, but without any kind of collateral damage. At the moment, I have standard electrolytics soldered in place, but I already got replacement tantalums that will get into that system some day.

mkarcher wrote on 2024-04-06, 11:44:

Trashbytes wrote on 2024-04-05, 09:21:

zuldan wrote on 2024-04-05, 09:05:

The Crystal chip has been ordered. Should I be replacing all the 10uF 16V Tantalum Capacitors on the board? There are 16 of them. Only 1 has a short.

If they check out ok and didn't pop the first time it powered up I wouldn't change them, but others here may have more experience with tantrum caps.

While I don't think I am a believer in the "recap everything" cult, the failure of Tantalum Capacitors is a general problem, not due to single faulty components. Most of the time, we see exploding caps rated for 16V on the +12V rail. If one tantalum blew on a system on power-up, I would recommend to swap all capacitors connected to the same voltage level, in that case, all tantalums that are on the +12V rail or the -12V rail.

As a personal, probably non-representative anecdote, I powered up a Compaq ProSignia server that was ~20 years in storage, and a tantalum on the mainboard popped. I desoldered that one, and tried it again, just to have the next tantalum pop after some more seconds of operation. After the second blown cap, I continued tests with the system outdoors, connected through an extension cord, so the smell stays outside. All three tantalum capacitors connected to +12V and finally the tantalum capacitor connected to -12V popped, but without any kind of collateral damage. At the moment, I have standard electrolytics soldered in place, but I already got replacement tantalums that will get into that system some day.

The first protects the second and so on down the rail, I guess they would act much like a fuse when they fail.

Personally, I try to avoiding using 16v types altogether.
For some reason, that's apparently the type of capacitors that fail the most.
Using say 25v types somehow feels better. I guess it's because 16v rating is a tad bit too close to the 12v, leaving little room for tolerance (thinking of ripple, quick voltage spikes etc).
Something similar can be said about 6v caps on a 5v rail, I suppose. Then there's the ESR thing..

Edit: I vaguely remember something. I once heard that ideally, caps should be rated twice the voltage they're going to be used with for.
If true, a 25v cap for a 12v circuit isn't too awkward.
Or a 10v cap for a 5v circuit, too.