Help! I have built dozens of the same PCB circuits using a single 555 timer (astable mode), but am having a bizarre effect when building the same circuit on a breadboard. If I build the circuit using a 555CP, the chip works fine (confirmed with o-scope). If I replace it with a 555CN, it does not (appears monostable). Swapping back in the 555CP and it works again. None of the chips are faulty, as they are all (both CP and CN versions) functional when swapped into the various PCB circuits. I've used and observed this phenomena with LM555CN, NE555N, and TLC555CP chips. All experts are welcome to weigh-in and are kindly thanked in advance.