Service manual

CA-9
IF Receiver
Tuner
Cable or off-air signals are received into the television by way of the antenna jack of the tuner, TU6000.
The input and output impedance of this device is 75 ohms. It provides for 181 channels (including cable).
It uses +33V for tuning, +5VTune as tuner B+, +4.3V for AGC, and on some chassis +9VSW.
As with standard varactor tuners, varying voltage across an internal varactor results in a different internal
resonant frequency, whereby tuning of the various channels is achieved. Control of this process is accom-
plished through the I
2
C (serial clock and data) lines attached to pins 4 and 5 of TU6000. These transfer
control data to and from IC6000.
AGC (automatic gain control) voltage is applied to pin 1 of the tuner from pin 3 of ICX2200. This DC
voltage varies in response to signal strength from the tuner so as to avoid signal distortion not only from low
signal levels, but also from signals strong enough to otherwise cause clipping distortion. AGC voltage will
alter the signal level accordingly.
<<Figure CA-8>>
IF Processor
Tuner IF (intermediate frequency) comes from pin 11 of the tuner. This is filtered and amplified (see
Q1200, U1200, and surrounding circuitry) before it is fed into pins 7 and 8 of ICX2200, the IF/video
processor (sometimes called the Jungle chip). IF consists of PIF (Picture IF), SIF (Sound IF), and CIF
(Chroma IF).
+33V
+5VTune
+9VSW
ZD6001 C6032 C6031M
C6030 C6029M
L6000
CX6027
C6026M
TP6006
TP6005 IF
TP6010
C6090
PROV
C6070
PROV
Clock2
Data2
TP6004
C6028
J6000M **
RF-AGC
** ONLY FOR 175-2771 TUNER
OMIT FOR 175-2771 TUNER
From Pins
36 and 38,
IC6000
11
10
9
8
7
6
5
4
3
2
1
TU6000