Service manual

CB-10
CB CIRCUIT DESCRIPTIONS
comes from pin 11 of the tuner, is filtered, and is fed into pins 5 and 6 of the IFP. AGC (automatic gain
control) voltage is applied to tuners pin 1 from pin 10 of the IFP. The +33VSB tuning voltage is applied to
pin 9, while the +5VTune processing voltage is on pin 7. Clock and data lines from IC6000 communicate
with the tuner on pins 4 and 5. In some receivers, the secondary tuners use the +9VIF at pin 6.
IF Processing
Each IFP is powered by the +9VSW on pin 9. After IF is received at pins 5 and 6, sound IF is separated
from picture IF emitted from pin 17. It reenters the IFP through pin 24 and finally exits through pin 1 as a
composite audio signal. Composite audio from each IFP enters a switching transistor array with part
designations 1290 through 1299. The audio-swap line from the microprocessor controls Q1292. This
transistor switches the rest of the array between composite audio from either the primary or secondary
tuner.
<<Figure CB-10>>
Two variable coils are available with each IF processor for adjusting AFC or VCO. Use caution when
adjusting these, and be certain to mark their initial position in case they need to be adjusted back to their
previous setting. A potentiometer is also available off pin 4 of the IFP. This adjusts the AGC delay inside
the processor.
1
2
3
4
5
6
7
8
9
10
11
12 13
14
15
16
17
18
19
20
21
22
23
24
DET-OUT SIF-IN2
1ST-SIF-AGCFM-DET
IF-AGC2 SIF-OUT
RF-AGC-ADJ VIDEO-OUT2
IF-IN1 EQ-FILTER
GND
EQ-INIF-IN2
APC-FILTER
SIF-IN1 VIDEO-OUT1
VCC VCO2
RF-AGC-OUT VCO1
AFT1 AFT-OUT
AFT2 IF-AGC1
IC1250
R1265M
C1270
TP1255
C1271M
R1266M
R1267M
+9VIF
C1285
R1268
C1272M
L1254
VCO
R1272M
C1273M
R1271M
C1274
TP1254
L1255
U1252
R1270M
R1269M
C1277M
R1273M
Q1251
C1276M
U1253
R1286M
PROV
+9VIF
R1278M
R1276M
R1256M
R1257M
CR1250
L1251
C1259
C1261M
C1260M
R1259M
R1258M
C1264M
C1265M
+9VIF
C1267M
C1266
R1261
C1262M
R1260M
R1262M
L1252
C1263M
C1269M
L1253
AFC
C1268M
R1263M
R1264M
+5VTune
+33VSB
TP1250
ZD1250
C1256
C1255M
C1257
C1254M
J1250M
C1258
C1253M
TP1251
C1250
C1288M
PROV
C1287M
PROV
R1251M
R1250M
SDA2
SCL2
Q1252
Q1253
+5VSBF
IF2-Video
AFC2
C1278
R1279M
C1279M
R1281M
R1280M
C1280
R1284M
C1282M
R1285M
C1281M
R1283M
R1282M
1
2
4
5
3
U1251
L1250
PROV
+9VIF
Comp-Aud-2
SD2
TP1253
TP1252
2nd-IF-Tuner
11
10
9
8
7
6
5
4
3
2
1
WT1250
AGC
Delay