Kenwood TM-731A Service Manual page 6

TM-731A/E
CIRCUIT DESCRIPTION
¢ Muting Circuit
There are three types of audio muting:
MU2 : Mutes the subband when the CTCSS key is pressed.
MU3 : Operates when the MUTE key is pressed on the front
panel.
¢ Speaker selection
In the TM-731A/E, a selection between the separate and mix
modes is made depending upon the connection between the
speaker output and the external speaker. (Refer to Table 6-1.)
When the separate mode is engaged, an attenuator is insert-
ed for level adjustment. (Refer to Figure 8-1.)
16
MAIN AF
co +
yo
t3 pin
95
Mutes audio output dur-
ing momentary memory
on
scan during transmission
en
sue AF
Ic , AOM
3pin 3
Ql3 2
© ———----_—|-——0
Aos
ie) & Tt
_ | & SHIFT
£
+:
REGISTER
82°
om
MUTE
C3
Qs MUI
Mu2
MUS
7 (e)
SUB BAND [Sus BAND MUTE Active
2048 MUTE /
High
/ Mutes subband Microprocessor
Operates when MUTE wher CTCSS data
control is pressed
on front panel
Fig. 8 Mute Circuit
p———_—«—Main AF signal + buzzer
+
t
Bc oa i |
oo R53
A eSure Sub AF signal
a © a :
« c3
. TC4053BF MAIN output to pin 1 of IC4
* only in separate mode
CN4 o
MSS
L—_____»
Figure 8-1 Speaker separate circuit °
MAIN/SUB output to pin 14 of IC4 in mix mode
- SUB output in separate mode
Connected only to (Connected to both
Without extemal | Connected only MAIN "SUB. MAIN and
AF
speaker
to MAIN terminal .
MAIN/SUB
;
terminal
.
signal terminals
. External speaker
Main
internal speaker
External speaker | External speaker
{connected to MAIN
terminal
External speaker
Sub Internal speaker internal: speaker | External speaker connected to
IMAIN/SUB terminal
Mix Separate Mix Separate
Table 6-1 Correspondence in connection between
speaker output and external speaker