User Dpc Adjustment Circuit; Afc Ihorizont Al Osci Llator - Tatung OMNISCAN SERIES Service Manual

TEST
CONDITION
Fh=31KHz
TEST
POINT
D1
TEST POINT NAME
NON-INVERTING INPUT
D2 INVERTING INPUT
D3 PARABOLA OUTPUT
D4 BUFFER OUTPUT
D2 2.3 Vpp
D4 5.5 Vpp
3.13 USER DPC ADJUSTMENT CIRCUIT
(Refer to circuit diagram Fig-13)
There are ten similar comparator circuit (0352c-
0352d, 0351a-0351d, 0350a-0350d) to achieve ten-
step user's DPC control function, all the comparator's
output is connected to the emitter of 0313 via
resistors (R370 to R381) to control the gain of the
amplifier 0313. The user's OPC control voltage is fed
to the inverting pin of the comparator, the non-
inverting pin of the comparator is connected to 16V
via resistor chain R382 to R392. This resistor chain
gives each non-inverting pin of the comparator
different dc voltage. Obviously the voltage on pin 2 of
0350d is higher than the voltage on pin 7 of 0352c.
When the voltage on non-inverting pin is higher than
inverting pin, the output of the'
compara~or
is
grounded.
So when user's OPC control voltage is getting higher,
the emitter impeadance of 0313 is lower. Then, the
output of 0313 is larger.
The parabola signal is fed to horizontal circuit via
C632-R651 to modulate the horizontal deflection
current in the yoke.
USER DPC CONTROL CIRCUIT
Fig-13
R370
B.':K
1/4'N
10 03 13.-.....-::..t-h--<O
OPC
AMP.
R371
221<
1/4W
R372
271<
I/G'N
R373
301<
I/G'II
R381
20K
IIGW
I
I
641<lHIGH}
4BKlHIGH}
OPC CONTROL ..
R391 R392
II< II<
1/6W 1/6W
I
I
R384
~II<
1/6W
R383
IK
IIGW
1
f "'" ' " '"
f
;;~o
1-=--4----·-w.-"16V
• C352 R382 .
IO:.! 15K
Z5V
!/6W
3.14 AFC/HORIZONTAL OSCILLATOR
(Refer to circuit diagram Fig-14)
The phase detector part of the Q403 (LA7851 scan
processor Ie.) is used to synchronize the output of
= 3-11 =