Service manual

13
Circuit Description
Push-To-Talk Transmit Activation
The PTT switch on the microphone is fed through the
PTT controller, Q1002 (UMZ2N), to pin 41 of micropro-
cessor Q1014, so that when the PTT switch is closed, pin
18 of Q1014 goes high. This signals the microprocessor to
activate the TX/RX controller Q1017 (UMG2N), which cut
off the receiver by disabling the 5 V supply bus at Q1020
(DTA143EU) which feeds the front-end, FM IF subsystem
IC Q1049, and receiver VCO circuitry. At the same time,
Q1037 (UMW1) and Q1041 (DTA143EU) activates the
transmit 5 V supply line to enable the transmitter.