Q1. switchers in serial circuits.
chip heating up to 60-70 degree C but keeping operate with a high current
consumption in circuit of negative potential of power supply.
Althogh current through any S and D pins is low.
2. swichers for selection of output (from first one or several consequent
serial op. amp.) One of the channels destroys.
In "ON" state either of chanels its S and D pins aquires Vss potential. Althogh
AC signal is ON.
In "OFF" state this DC potential disappear and the chip is OFF.
P.S. Initially all chips operate in a due mode. Prolems appear once power is
swiched off for recommutation of a chanel from High to Low level on "IN" pin.
AIf you suspect damage to parts, heating up, consuming excessive current, the
place to look is the Absolute maximum ratings for the IC.
This says that the logic supply VL must be between -0.3V and VDD + 0.3V at all
times (including power up and power down).
Also spikes on the signal lines which go outside the supplies will cause the
part to latchup. You mention capacitive coupling of signals - this could allow
the signal to go outside the rails for a brief period of time.