Kenwood TH-F6A Service Manual page 12

TH-F6A/F7E
5. Lithium ion battery charging control
If a lithium ion battery is installed, it is charged when power
is supplied to the DCIN JACK from outside. The mechanism
of charging control is described below.
When power is provided to the DCIN JACK, Q65 turns ON
and the control port is made LOW to notify the CPU of
connection of an external power source. The CPU grounds
the Q2 collector according to this information. As a result, Q5
turns OFF and Q1 turns ON. If the remaining battery level is
low, the Q1 collector current increases, so the emitter voltage
is reduced by R2 and Q2 turns ON to charge the battery
(charging). The CPU pulls up the Q2 collector voltage, uses
this port as input, and monitors it. If the battery voltage level
increases, the Q1 collector current decreases, the emitter
voltage drops and Q2 turns OFF at a certain voltage. The CPU
recognizes that charging is approaching its end by this change,
and enters an additional charging state. In the additional
charging state, the CPU grounds the Q2 collector and
continues charging slowly in about an hour. When it ends,
the battery charging is complete.
IC1 is a lithium ion battery charge control IC. When the
battery voltage exceeds 8.4 V, the output port is made HIGH
and Q3 is turned OFF to stop charging. If it is 8.4 V or lower,
"LOW" is output and Q3 is turned ON to bias Q1.
6. Receive audio circuit
The receive signal demodulated by the FM IC on each of
the A and B bands passes through an electronic volume (IC706)
and is amplified by IC717. The signal is deemphasized by
Q719, passes through a variable RESISTOR (AFVR), is
amplified by the audio amplifier (IC707), and output to the
speaker (SP1) or external speaker jack (J701).
CTCSS or DCS is a 2-channel multiplexer from FM IC output,
and A or B band is selected, the signal passes through an
amplifier filter (IC711), and goes to the CPU where it is
decoded.
TA31136FN
FM
AM
IC5 UPA672T
TK10931V
SSB/CW
7. Transmission signal system
7-1. Modulation circuit
The audio modulation input is switched between external
input and internal microphone using an external microphone
terminal, and its base band is processed by microphone
amplifier IC 702 and preemphasis/limiter IC 701. The signal is
mixed with a DTMF subtone before the preemphasis circuit,
the level is adjusted by electronic VR IC706, and the signal is
input to the VCO as a modulation signal. The excessive input
of the 9600bps packet signal and the high-speed FM mode
12
CIRCUIT DESCRIPTION
IF DET
IC706
M62364 FP
IC7
SW
Q22,29
SW
IC712
TC4W53FU
SSB DET
IC4
TA4101F
IC711
TONEIN
TA75W01FU
TONE FILTER
L3
J1
CN1
CN2
Q1
2SD1760
CHG
D5
15S361
The 9600bps packet signal is produced by converting the
impedance of the output signal from the FM IC by Q720 and
Q721, passing it through the Q722 switch, and outputting it to
the speaker (SP1) or external speaker jack (J701).
AMP DE EMPHASIS MUTE SW AF VR
IC717 Q719 Q704
TC75 2SC4617 2SJ
S51F (R) 347
Q720
2SC4617(R)
Q721
2SJ347
Q722
2SK1830
SW
Fig.18
SSTV transmit signal input through the external microphone
input terminal is suppressed by D710 and D711, switched by
IC703, and input to electronic VR IC706. The level-adjusted
signal is amplified by Q719, passes through electronic VR
IC706, and is divided into two paths: one for modulating the
VCO through electronic VR IC706 the other for modulating
TCXO X1 through amplifier IC702 to perform broadband
transmission modulation.
F2 F1
C23 1000p
C24 100p
4A 2.5A
Q65
D6
2SK3019
RB051L-40
R23 22k
D7 DA221
IC1
LM3420-8.4
Q3
DTA143ZE
1
5 OUT + IN
2
GND
3
COMP NC
4
Q2
DTC123JE
Q5
2SK1830
Fig.17
DTMF BEEP
AUDIO AMP MUTE SW
Q706
IC707
2SK1588
TA73
Q708
68F
2SK1830
B
DCDET
CHG1
VTx
SP
SP