Kenwood TS-440S Serivce Manual page 21

TS-440 S
CIRCUIT DESCRIPTIO N
4 . Static input
7800 (ICI )
C O
C 2
07
Encoder U/D signa l
Unlock signa l
4052 (IC : Display)
"H" when U P
"L" when unloc k
A/D convertor dat a
8255 (IC53 )
B O
B 2
B 3
B 4
B 5
B7
Lock switc h
AT switc h
MIC UP switc h
MIC DOWN switc h
PTT switc h
VS-1 busy signal
"L" when switch o n
"L" when switch o n
"L" when switch o n
"L" when switch o n
"L" when switch o n
"H" when VS-1 busy
6 . AT control
L
A/D converter Inpu t
Fig . 17 A/D convertor circui t
2 9
--%--- 1
A K
D O
I
Table 1 1 .
5 . A/D convertor inpu t
Voltages controlled by the RIT and IF shift VRs are applie d
to the 4052 (IC2 : Display) . The 4052 has four analog inputs :
AO (IC2 pin 4) is connected to the IF shift VR, and Al (pi n
5) is connected to the RIT VR, the other two inputs are no t
used . When reading IF shift data, the 7800 sets port C5 t o
0 and selects 4052 AO . As a result, the 3255 sends a posi -
tive pulse from port BO to reset the 4052, and the 780 0
sends nine positive pulses from port C6, and port C7 receive s
data . When reading RIT data, the 7800 sets CO from th e
4052 to H and thereafter performs the same operations as
when reading IF shift data .
When the AT switch is turned on with the AUTO/THR U
switch in the AUTO position, 8255 (IC53) ports B2 and B 5
go on . When the 7800 knows that the AT switch is on vi a
port B2, it will enter the CW-mode, and sets port A2 to H
and A0, Al, and A3 to A6, and B4 to L, and transfer a pow-
er down signal . The 7800 then knows that the PTT switc h
is on via 8255 port B5, and sets port A6 (transmission con-
trol signal) to H, enabling transmission . However, if the select -
ed frequency does not allow the 7800 to prepare fo r
transmission, 7800 port A6 remains L and the 7800 will no t
enable transmission . When the selected frequency is 1 .9 MH z
or less, the 7800 will not enter CW mode nor send a powe r
down signal .
7. LED outpu t
Depending on the mode, the 7800 makes the 8255 (IC2 )
send M, SCR, 1 MHz, and lock LED signals from ports B4 ,
B5, and B6 . When the LED goes on, these ports are L .
When the mode LED is on, 7800 ports AO to AS are H . A O
to A5 correspond to LSB, USB, CW AM, FM, and FSK respec -
tively . Mode LED output is used as mode control signals i n
the IF unit .
8. VS-1 (option )
When the voice switch is turned on, an address correspond-
ing to the instruction (numerical data) entered is sent fro m
8255 (IC2) ports AO to A4 and a positive start pulse signa l
is sent from port A5 . The VS-1 sends busy signals (H) to
8255 (IC53) port B7 while the voice switch is on . After th e
voice switch goes off, an address corresponding to the nex t
instruction and a start signal are sent .
9. µPD 7800 reset circuit
The 7800 reset circuit is used to initialize the 7800 whe n
the POWER switch is turned on . This circuit supplies a rese t
pulse to the 7800 after the clock is supplied to the 7800 sys -
tem clock input, X1 (pin 31) . Since IC3 remains on unti l
PST520D (IC3) pin 1 reaches 4 .3 V, C10 is not charged, ena -
bling a reset signal to be supplied . When pin 1 exceeds 4 . 3
V, IC3 goes off, causing C10 to charge via R2 and R3 an d
the reset signal is removed .
I) RIT
2) IF SHIF T
MB 4052
2 1