cd4051 bug?

I made a project using a 4051 to select one of 5 inputs. I take the output fro pin 3. I used addresses 1, 2, 3, 4, and 5. Some times I have signal out when there is no signal at input 4 but there is some on input 3. It is kind of a crosstalk. But it only happens between inputs 3 and 4 and never in others. I have made about 1 hundred devices and had problems say in 15-20 of them. Is that a bug of the 4051? Some one heard of something similar?

Load impedance = 10 K R to ground - Frequency = fix @ 5 KHz - Definitely not capacitive coupling. All 5 channels are equal,the 5 signals are the same - only jumps from input #3 to #4 - strange, isn't it?

Aer all inputs terminated with the appropiate HI or LOW levels and not open wen you move the signal from one input to the other?

YES: if one over-drives an input, it can latch - and if overdriven too much, then the input can act as if it is always Hi even if grounded.

Millions of 4051 chips have worked as expected, so I doubt you have discovered a design bug.

Suggestions :

A batch of weird chips ?

You are pushing logic or analog pins too high or low and getting interconnection via substrate current flow ? For example, driving from opamps with more swing available than the 4051 power rails.

The VDD, VSS, VEE voltages are not what you think they are ?

Roger

I know that if you drive the input past 0.6 Volts over Vcc or minus 0.6 V under Vee it will latch or crosstalk. That is not the case. Vcc is +5.0 coming from a 78L05, digital lines come from a PIC 16F84A at +5.0 Volts also. On analog lines I tried everiything form biasing them at 0 Volts to coupling by capacity to let if self-bias. No results. Forgot I mention that all 5 signals are identical?

Resolved. Tanks to you all, friends. As always the problem was out of the circuit and is clear now. I used a set of pre-amps to amplify the signal of photo-diodes. On some sets, the boys (installers) used to run the wires of the input to one pre very near the output of another pre. Simply basic cross-talk. And always happened on channel four... because of the topography.