>  One minor suggestion/question for the list, would it be better to
put
>the Zener or catch Schottky's on the output pin of the 54C14J, or at
the
>outside (past the output resistor), at the cable connection?  That's
>where I'd be tempted to put them, then any HV noise put into the the
>cable is solved right there - you cannot get up *to* even 30 volts
on
>the other end of that 54C14J output resistor.


With the diodes at the IC output AND a resistor on the PCB before the
cable the diode sinks current when the "spike" is dissipated across
the resistor. The resistor takes the brunt of any voltage spike.
Diodes should be Schottky to keep drop below 1 silicon junction drop
and also are "fast". Diode power is low as it is 1 Schottky junction
drop x the available fault current. If a zener is placed outside an
on board resistor it has to dissipate all the energy itself. Gruntier
diode needed and runs the risk of being driven quite high if spike is
fast.

>  Also, Kelly, one question:  Your web page doesn't give relative
>quantities made of the various units, some sort of "The failure rate
IS
>(or IS NOT) fairly uniform across models made" information might be
good
>to provide people in some cases, you could provide that without
>disclosing sales data directly (in case that's sensitive
information.)
>In this case, I suspect it's that cable/54C14J connection.


He implied that there were probably about 1000 all up - he has not
been given the exact figure I think.




regards

            Russell McMahon