Other Parts Discussed in Thread: SN74HCT165, SN74HCS165
Hope you're well!
My customer recently swapped out a SN74LS165AD for a SN74HC165DR on their board and are now experiencing failures where they weren't before. Swapping the HC out for the LS fixes things.
It appears the HC165 isn't driving the lines.
You can see the HC165 start to drive the line low, but the signal would go back high prior to being clocked in (Green is data out of the HC165, Red is CLK to the HC165, and Blue is the Data Load signal to the HC165).
In this case they expect the bit on the first clock cycle to be low, but it goes back high prior to being clocked in.
Output with the LS165 as expected
I asked for a schematic but they don't keep their old schematics (this is for an old production design). Do you forsee any issues with the swap that may be causing this?