[Collins] KWM-380 parts

[Dr. Gerald N. Johnson, electrical engineer]

Yes, you can look at the logic function with a scope. Sometimes it works
best with a multiple trace scope so you can look at inputs and output at
the same time. You have to compare the inputs and output with the logic
function, or you can be confused. E.g. just because an input of a 7400
jumps around, if the other input is held low the output won't change
from being held high. Just the opposite for a 7402, there if one input
is held high, it doesn't matter what the other input does the output
will stay low.

I've seen such chips fail shorting inputs together. The scope sometimes
shows that as an input wiggling along with an adjacent input, but not to
full logic level.

One other really handy tool is a logic comparator. HP sold the kit long
ago, has a board for each chip to be tested and compares the device on
that board to the device on the board being tested. Kind of the analog
of a tube tester. Shows up logic differences, but may not find the
shorted inputs.

73, Jerry, K0CQ, Technical Advisor to the CRA
-- 
Entire content copyright Dr. Gerald N. Johnson, electrical engineer.
Reproduction by permission only.