Kenwood TKR-740 Service Manual page 42

TKR-740
5.7 M icrophone AGC circuit
The microphone AGC circuit AGC-amplifies an audio signal
coming from a local microphone so that it does not overdrive
the modulator. This circuit consists of IC23, D707, D709, Q700,
and Q701. The AGC is operated by controlling the + and -
levels of amplitude using the current obtained by positive and
negative detection of the amplified audio signal.
Fig.27 M icrophone AGC circuit
5.8 RS-232C circuit
The RS-232C circuit connects the RS-232C serial port of a
personal computer directly to this model to perform FPU
operation. The FPU operation can also be performed by
connect ing a program m ing cable (KPG-46) t o t he local
microphone on the front panel. If the D-sub connector on the
rear panel is used, the programming cable is not required. The
232C driver IC (IC42) changes the TTL-232C level. The FPU
(KPG-47D) has a new transmitter/receiver circuit monitor
function (transmitter: forw ard pow er, reflected pow er display,
transmitter main PLL lock voltage; receiver: RSSI display,
receive main PLL lock voltage). Data required for this function
is also transferred through the RS-232C serial port. The
firmw are can only be rew ritten using the local microphone
connector on the front panel.
Fig.28 RS-232C circuit
42
CIRCUIT DESCRIPTION
5.9 Pow er supply circuit
CPU, DSP, flash ROM , bi-directional buffer, and baseband
circuit. This circuit consists of IC3, IC4, IC5 and IC6.
The pow er supply circuit generates pow er to operate the
Fig.29 Pow er supply circuit