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Lorenfb Lorenfb is offline
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Join Date: May 2003
Location: Manhattan Beach, CA
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When the EPROM chip is installed backwards, the VCC (normal +5 volts) and
the VSS (normal GRD) get forward-biased which results in a large substrate
current on the chip. This can in some cases damage the chip, e.g. some of
its inputs or outputs. It's fair to assume that if it can be read by an EPROM
reader, then it can be read by the 8051 in the DME.

The problem which occurs, though, is that when the substrate is forward
biased, the other chips connected to the EPROM are subjected to possible
heavy loads on their inputs and outputs. This may or may not damage the
other chips, e.g. the 8051 or the A/D converter. It's just not a good idea
to have the EPROM in backwards.

If it's a cracked circuit board or a bad solder connection, it's not easy to
find the problems without checking all the signals using a scope. A lot
of connections may look bad but are usually good and vice versa.

Good Luck
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Old 12-31-2003, 07:32 AM
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