Tantalum Popcorn - What to do (Was S-100 Bus Voltages)

From: Richard Erlacher <edick_at_idcomm.com>
Date: Mon Jun 4 17:28:25 2001

While the generalized observation that when something pops, there's a good
reason, in the case of tantalum cap's it's often simply the age of the cap.
They don't age gracefully and it's not at all unusual for the only thing wrong
with a board that bursts into flame to be the cap's that were engaged in the

If you replace the tantalum cap's it's likely the problem will be gone.
However, if you leave one of the old ones on the board, it will "go" later, for
you to clean up later.

Not all such aged cap's will catch fire, though the tantalum ones tend to do so.
Some will just short, causing your power supply to act funny, since they're
quite a large load. That's what makes 'em catch fire when they do.


----- Original Message -----
From: "Sellam Ismail" <foo_at_siconic.com>
To: <classiccmp_at_classiccmp.org>
Sent: Monday, June 04, 2001 1:55 PM
Subject: Re: Tantalum Popcorn - What to do (Was S-100 Bus Voltages)

> On Mon, 4 Jun 2001, Edwin P. Groot wrote:
> > Well, I plugged in the boards and powered up the computer, and
> > promptly powered it down after a few loud pops - D'Oh! Nothing was
> > displayed on my teminal connected to the console serial line. The affected
> > boards are the CPU board and a serial board - some tantalum capacitors
> > blew. I'm assuming they're tantalum caps- they're not electrolytic
> > can-style, or ceramic disc-style, but look like a gob of shiny blue acrylic
> > paint on two leads. The board marks which lead is +.
> > Are these tantalum caps common enough to buy at the local electronics
> > shop? We've got Radio Shack, but I heard they are overpriced. The caps to
> > be replaced were in the uF range.
> > BTW this is a complete system and the cards are arranged (from low
> > slot # to high slot #): CPU, RAM, FD controller, Serial/Parallel,
> > Terminator. Will check with documentation that RAM and ROM banks, and I/O
> > is configured right once I get the boards fixed.
> I had this experience before with a Sol-20. Aside from being loud and
> smelly, the tantalum caps exploding really shouldn't hinder the operation
> of the system. Tantalum caps on older systems like S-100's that haven't
> been powered up in some time are prone to exploding.
> If you have a problem it's most likely related to some other failure.
> Perhaps you should check to make sure you have matching settings on
> your serial port and terminal. Also, make sure your cable is the right
> kind (straight through...NOT a "null-modem" cable).
> Also, maybe your system is expecting a boot disk to do anything useful.
> Did you notice if your drives are spinning when you fire it up?
> Sellam Ismail Vintage Computer Festival
> ------------------------------------------------------------------------------
> International Man of Intrigue and Danger http://www.vintage.org
Received on Mon Jun 04 2001 - 17:28:25 BST

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