5. Reference oscillation circuit Although there are two oscillators, X131 (24.576 MHz) and X132 (25.438 MHz), for providing the reference oscillation used to drive the various ICs, the one normally used is X131. However, when receiving an AM bandwidth signal, only when the reception is within a certain specific frequency range, the X132 reference oscillation will be used in order to suppress interference from the reference oscillation during AM bandwidth reception. The switching of the reference oscillation is performed by a command output from pin 67 of the microprocessor (IC941). The output from pin 67 is normally L, and it changes to H (high) only during reception of an AM bandwidth signal that is within the specific frequency range. That H signal causes Q002 in the digital amplifier circuit to switch on and drive IC019. (Normally IC019 is off and IC018 is driven.)
+B Pin 67 of IC941 (frequency shift) Pin 1 of IC011 (24.576 MHz) Pin 47 of IC012/013 (12.288 MHz) Note : The 24.576-MHz output is divided 1/2 at IC020 to generate the 12.288-MHz output
