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dc voltage on pin 4 of 0122.
Naturally gives the
Potentiometer R141 and R152 are the GAIN control
bigger amplitude for the output and more colorful
for
the
preamplifier 0122, also enable the color point
picture on the screen.
of the monitor optimized during set up.
CONTRAST CONTROL/BLUE PREAMPLIFIER CIRCUIT
Fig-42
5001
SIGNAL LEVEL SW.
°O.T'P
~
D-l'----.,
R02? 0057
12V .. · - - - - - 1 - 0
RO'i2
18
NP
43
ISS 176
CO! I
1104'1'.
' "
0')50
155176
RI39
?SO
BoOR:H:
",:0
r1"
1
~
m
5.'1(
!:K
'RIS''::
~~-Jo.t,
!:K
0128
2SAIOl5Y
ABL INPUT
P009
.1"~~---~~--~--&-~~--~r---~------~r-------rL
1
B.DRIVEl
~
D058
1
CI03
rg0
5
R024 tCI15
CliO
J
154J
16V
II<
IOU
T104'(
!N414B.1
Cr;:93M - - - . . .
.
16"1
.l
CD
liP
"ICC
G
R721
' : :
0055,;"
T
':"
'J047
2SC18!5Y
ABL
CI13
J
103Z
IN4148
CI)NTRAST
AMP.
101(~
__
~
________________
~
CONTROL
·'R.
R723
3.9K
el19
1
474
': 6.3'01
Rl43
5. II(
. .
®
0122
~:;1399P
!d'
CLAMP
PULSE
4
GAIN
FE.E.D
CGNT
BACK
C!40
2.'lU
®
VIDEO
50"1
..
@
HOLD
Ci..AI .. 1P
CAP CONTROL
(J)
GND
VIDEO
OiP
3.43 ABL
(AUTOMATIC BRIGHTNESS
LIMIT)
CIRCUIT
D508 is negative pulse by-pass diode.
(Refer to circuit diagram Fig-42/43)
The ABL circuit in fact is a voltage feedback circuit
which varies the gain of all three video channels
simultaneously.
The negative feedback signal is
proportional to the anode current of the CRT.
The voltage on pin 9 of T603 is the voltage drop of
+
73V via R630. The component value is selected so
as to limit the maximum current of the CRT. (400JLA
approximately)
The signal is fed to the base of ABL control stage
0047 via pin 1 of P009. The higher voltage on pin 1,
means the darker of the picture, the lower voltage on
pin 1, means the brighter of the picture. So via 0047,
this signal will control video gain and limit the CRT
current automatically. .
.
.',:
The ABL signal is also fed to the base of 0008-0068-
0128 via C085-D055 to get stable ABL function.
ABL CIRCUIT
1603 FBT
lFB-23BM
=
3-36
=
{3
G
([Y
(9
®
®
Fig-43
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