Re: need motherboard recommendation
* Doug <dmcgarrett@optonline.net> [101226 22:56]:
> Maybe it's time to buy tantalum capacitors. More expensive,
> slightly smaller, and (I believe) less likely to blow up. Available
> with parallel wires or in surface mount configurations. Military
> equipment has been using tantalum caps for years, so they must be
> reliable.
Tantalums are good, but manufacturers consider them a little too
expensive for mass-produced motherboards. Tantalums are valuable when
you need high capacitance in a high-frequency application; the
capacitance of electrolytic diminishes rapidly with increasing
frequency. This is why you often see two or more capacitors in
parallel; typically a tiny, low-value ceramic (which has excellent
high-frequency performance) is paralleled with a high-value
electrolytic -- and the combination still is less expensive than a
single tantalum.
You can make almost anything explode (that is, fragment) if you apply
enough voltage and current. Years ago I had several clones of the
LM317 three-terminal regulator explode when the output was shorted;
this despite the fact that the data sheet claims that the device
withstands a short of infinite duration. I phoned National
Semiconductor and it was Bob Pease who picked up the telephone. I
began by saying, "I have some LM317s manufactured by one of your
competitors..." But before I could say another word, Bob interrupted
to ask, "Was anyone hurt when they exploded?" Bob went on to say that
National short-circuit tested every LM317, and "the ones that explode
don't get shipped." It is episodes such as this that have made Pease
a living legend among electrical engineers.
But even if you manage to blow up a tantalum, there is no electrolyte
to spill.
%%%
If I recall correctly, the problem which I cited was caused by
manufacturing changes regarding the chemistry of electrolytics. The
problem eventually was solved by further manufacturing changes in the
chemistry of the electrolytics, but not before a great many
short-lived motherboards were manufactured and sold. I remember that
Tyan in particular received much bad publicity from the matter, and
that some motherboards failed within three to six months of being
placed in service.
(Something similar happened with alkaline cells when the "get rid of
the mercury" mandate came out several years ago. It turns out that
mercury reduces gassing, and mercury-free cells gassed so badly that
they leaked electrolyte.)
Finally, I was in error regarding the P5Q-EM; it employs solid
capacitors only in the critical power supply circuitry surrounding the
processor; other capacitors on the board are electrolytic. This is
typical of the garden-variety motherboards which I see on display at
the local electronics emporium.
RLH
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