Hello All,
Will someone with a little testing savvy explain the basics of guarding to me. Let me
give you an example. This board is populated with 74HC, which is not good stuff to
short high or low, as it is driven both ways. The databus has eprom, cpu, & 3 support
chips with /CE going to a 74HC138. That device I desoldered, and the Eprom was pulled,
to test the support chips.
/RESET on the cpu is driven from a watchdog chip, via a 74HC4049
/STDBY is wedded to +5V, and things fail. I grounded the /RESET anyhow and what I'm getting
is a fail like "H(or L) expected - Z received" from every output pin. The chips are an 8255 and a 6840.
Additionally, the 6840 fails an opens test on random pins
The board is known to work. It has been tested and returned to me.Am I safe pulling 74HC o/ps
low? High? It's only switched in fior the functional test, btw, and the devices are not
continuously powered.
How does one go about solving this sort of thing?
TIA from the learning curve
Declan Moruarty
-- Author: Declan Moriarty INET: [EMAIL PROTECTED]
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