Hugo,
To follow up on Michael's excellent advice, I have also seen socketed DIP ICs in a 475 (very similar to the 465) where the pins have become tarnished in the socket and are no longer making electrical connection. I diagnosed this problem by tracing the signal to the IC in questions, then checking connectivity between the trace on the board and the leg on the IC (and seeing that there was no connectivity). So even if the IC is not dislodged/missing, it may still not be connected to the circuit.
Removing the IC from its socket and cleaning the pins with a cotton swab soaked in isopropyl alcohol solved the problem.
-- Jeff Dutky
