Octagon 5420, User Manual

Using CMOS Circuitry in Industrial Control

Industrial computers originally used LSTTL circuits.  Because
many PC components are used in laptop computers, IC manufac-
turers are exclusively using CMOS technology.  Both TTL and
CMOS have failure mechanisms, but they are different.  This
section describes some of the common failures which are common
to all manufacturers of CMOS equipment.  However, much of the
information has been put in the context of the Micro PC.

Octagon has developed a reliable database of customer-induced,
field failures.  The average MTBF of Micro PC cards exceeds
11 years, yet there are failures.  Most failures have been identified
as customer-induced, but there is a small percentage that cannot
be identified.  As expected, virtually all the failures occur when
bringing up the first system.  On subsequent systems, the failure
rate drops dramatically.

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Approximately 20% of the returned cards are problem-free.
These cards, typically, have the wrong jumper settings or the
customer has problems with the software.  This causes
frustration for the customer and incurs a testing charge from
Octagon.

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Of the remaining 80% of the cards, 90% of these cards fail due
to customer misuse and accident.  Customers often cannot
pinpoint the cause of the misuse.

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Therefore, 72% of the returned cards are damaged through
some type of misuse.  Of the remaining 8%, Octagon is unable
to determine the cause of the failure and repairs these cards at
no charge if they are under warranty.

The most common failures on CPU cards are over voltage of the
power supply, static discharge, and damage to the serial and
parallel ports.  On expansion cards, the most common failures are
static discharge, over voltage of inputs, over current of outputs,
and misuse of the CMOS circuitry with regards to power supply
sequencing.  In the case of the video cards, the most common
failure is to miswire the card to the flat panel display.  Miswiring
can damage both the card and an expensive display.

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Multiple component failures - The chance of a random
component failure is very rare since the average MTBF of an
Octagon card is greater than 11 years.  In a 7 year study,