2430 Super VGA Video Card – 4
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Improper power causes catastrophic failure - If a card has
had reverse polarity or high voltage applied, replacing a failed
component is not an adequate fix. Other components probably
have been partially damaged or a failure mechanism has been
induced. Therefore, a failure will probably occur in the future.
For such cards, Octagon highly recommends that these cards be
replaced.
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Other over-voltage symptoms - In over-voltage situations,
the programmable logic devices, EPROMs and CPU chips,
usually fail in this order. The failed device may be hot to the
touch. It is usually the case that only one IC will be overheated
at a time.
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Power sequencing - The major failure of I/O chips is caused
by the external application of input voltage while the Micro PC
power is off. If you apply 5V to the input of a TTL chip with the
power off, nothing will happen. Applying a 5V input to a CMOS
card will cause the current to flow through the input and out the
5V power pin. This current attempts to power up the card.
Most inputs are rated at 25 mA maximum. When this is
exceeded, the chip may be damaged.
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Failure on power-up - Even when there is not enough current
to destroy an input described above, the chip may be destroyed
when the power to the card is applied. This is due to the fact
that the input current biases the IC so that it acts as a forward
biased diode on power-up. This type of failure is typical on
serial interface chips.
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Serial and parallel - Customers sometimes connect the serial
and printer devices to the Micro PC while the power is off. This
can cause the failure mentioned in the above section, Failure
upon power-up. Even if they are connected with the Micro PC
on, there can be another failure mechanism. Some serial and
printer devices do not share the same power (AC) grounding.
The leakage can cause the serial or parallel signals to be 20-40V
above the Micro PC ground, thus, damaging the ports as they
are plugged in. This would not be a problem if the ground pin is
connected first, but there is no guarantee of this. Damage to the
printer port chip will cause the serial ports to fail as they share
the same chip.
