Kenwood TKR-851 Service Manual page 17

5-10. 5-tone* Decode
The 300 to 3000Hz frequency characteristics of the signal
that enters the comparator are made flat by the circuit, and
the band is made into that band required to detect 5-tone
signal by the low-pass filter (IC632 2/2), high-pass filter
(IC632 1/2) and BEF filter (IC631 1/2). The signal made into a
square wave by the comparator (IC631), and input to the
CPU, IC604.
R833
BIAS
IC611-7 pin
6. DC Power Supply Circuit
6-1. DC Source Switching Relay Circuit
1. The final unit contains a relay (K1) for switching between
the Main DC and Backup Battery.
If an external power source is connected to the Main DC
terminal, the Backup terminal is isolated by the relay. If
the Main DC turns OFF due to power failure, it is switched
to the Backup terminal by the relay.
The CPU monitors which is used, Main DC or Backup Bat-
tery.
2. Trickle charge circuit
If both Main DC and Backup Battery are connected, trickle
charging of 0.5 A max. can be performed from the Main
DC power supply to the Battery.
(The default is OFF. See the Modification section for infor-
mation on the modification method.)
The battery is charged from the Main DC with D8, D9 and
R61. If it exceeds 0.5 A, the charging circuit is turned OFF
by D9.
6-2. SB Switching Relay Circuit
1. SB (Switched +B) is supplied through the relay (K1) in the
TX-RX unit A/2.
When S507 (DC source switch) in the display unit is
turned ON, the relay (K1) is turned ON to output SB.
2. If +B exceeds 18V, the relay is forcibly turned OFF by D12
and Q25 to interrupt the power and protect the main unit.
CIRCUIT DESCRIPTION
R831
C838 C837
–
R832
+
IC632
(1/2)
IC604
P3
5TONE
Fig. 11 5-tone decode
IC604 checks the square wave frequency for the pres-
ence of the required tone, and if the tone matches, IC604
performs the subsequent required processing.
* : The 5-tone signalling is used only the E markets.
C833
R828
IC632
(2/2)
C836
R826
–
+
IC631
(2/2)
R818
–
+
R823 R820
Main
DC
D8
D9
R61
Land
Backup
battery
Fig. 12 DC source switching relay circuit
+B
R165 R166
D12
Q25
Fig. 13 SB switching relay circuit
TKR-851
R827
IC631
(1/2)
R824
–
+
BIAS
IC611-7 pin
R55
+B
K1
120mA
(Relay)
Final unit (A/2)
TX-RX unit (A/2)
TX-RX unit (B/2)
16
BUP
IC604
CPU
Q601
K1
SB
Land
(PSW)
Q24
Display unit
S507
(Front panel)
17