SECTION 3
CIRCUIT DESCRIPTIONS
3-1. OA, OB, BA BOARDS
3-1-1. Input Circuit
Cable Compensation (QA, QB)
CABLE COMPENSATION is composed of inductance L and
capacitor Cl (Figure I) in QA board and performs return loss
compensation.
Grounding or floating in input terminal can be selected by switch
s I.
On floating mode, common mode rejection can be performed.
QB board also has same function.
BNC
Figure 1
Hook Up Circuit (BA)
This circuit is composed of transistors QI O 1-105 and performs
common mode rejection when SW SI is selected to the floating
mode.
In Figure 2, Gains of amplifier for input A and B are derived as
follows.
A= ~f : Gain of amplifier for input A
B = -~f : Gain of amplifier for input B
When input (ec + ei) is applied to input A and
input (ec - ei) to input B, then output eo is
eo = ~f (ec + ei) + (- ~fl (ec - ei) = 2 ~fei
This equation indicates that ec is eliminated and there is no com-
mon mode signal in output signal.
On hook up circuit, NF Amplifier (Negative Feedback) is used to
get frequency response flat.
+Vee
eo
B
A
-Vee
Figure 2
Input Select Sw, Sync Select SW (BA)
For composite video signal, VIDEO A/B/TEST mode is selected by
INPUT SELECT SW (!Cl). For sync signal, INT SYNC/EXT SYNC
is selected by SYNC SELECT SW IC2.
3-1
3-1-2. Sync AGC Circuit
This circuit is composed of following components: LPF (Low Pass
Filter) (Q701), variable gain amplifier (Q702-Q705), bias control
circuit (Q708-Q710), gain control circuit (Q71 I, 712) and ampli-
fier (Q706, 707), Figure 3 shows block diagram of this circuit.
An inverted composite video signal or composite sync signal (eo)
is derived at the collector of transistor Q707.
The bias control circuit compares maximum value of eo with base
voltage of Q708 (El) and controls bias of amplifier so that they
match.
Also the gain control circuit compares pedestal level of eo with base
voltage of O71 I (E2), and controls variable gain amplifier so that
they match.
ei
L.P.F
VARIABLE
AMP
GAIN
CONTROL
Figure 3
AMP
i------eo
BIAS
CONTROL
Composite Sync Separation, Vertical Sync Separation
Composite sync is separated from composite video signal or com-
posite sync by comparing voltage eo with the base voltage of tran-
sistor Q713 (E 3).
Horizontal component in composite video signal or composite
sync signal is removed by LPF (Low Pass Filter, Q716) and Vertical
sync is separated by transistor Q717.
BLOCK DIAGRAM OF QA, OB, BA BOARDS
R, R-
,---(I (7o~)
--------- ------------- ----------- - ----~
~I '/10£0
~
INPUT
I
020i-2C5
--I
HOOK UP
~
cv,o, f f tRv20,
FREQ C
~
2C2 GAIN
•REO
0301-305
1"
G
CABLE lr----9----<,~--,
COMP I
-
J
_l
I
'100K UP
~
?SJ
--
e-----
0 /RGS/
B \COMPONEN"
INPUT
/~
~
~
COMP I
1
i'
I
'"
'7
J
CABLE I
I ';\
COMP I
I
--r-
I
("
I
.J
J
041)1 ..... 405
HOOK \JP
,v.0
1
I ?
FR[C
CY402
FREO
0501--..505
.I
I
HOCK IJP
CV50
1
f #
FREQ
(V':,02
FREO
,(RV4CI
GAIN
r--~
r~V501
GAlt,,j
J601 ..... 605
1(1
I 01,DZ
1NP1.,<":-SELECT
CONTROL
l
0
101-712
D701-705 0713-717 /-A_lt--Gc-Nc-O----j
.'.)709,710 D7C6'708 COMP SYN( BA2' GND
rl
I COMP SYNC
SYNC AGC J,-----, c~M;r~~NcsEs:P Iv SYNC e2 v.s.s
~.J:-.c;-1, .--;;B-;;o~u,--
1 '---<.J-;;cB,c;-1,--;;s-;;ou~,--,
02
~COMPv,oEG
~,-l.:::J1---------i
G~O
84
~A5
I L.~s::::s ;=::::G::::. ::ou::,===~
A6 GND
G ou~
se GNO
~A? ROUT
I Lo.rs~, t---c-R-,-o""',n,---;
r,-ce +----c,:--,:-o --;
BB GND
...-l-------------t-----t-+--i---'-1,-J-::c:c:t--~cc:-. •c-:---1
AIO GNC
S,Q GNC
A11: 5 SW
8 I
A,2
RGB SW
LC(AL, Rf MOTE
s,2
I
A13
B1j
Sr"iCSELECTSW~
,-----o--l.---l--t---J_+-+---ff'-'1t--_-;_,N"2_7i[1~[';',_,r._ye_-_l-,
~;-,; '0--~--1-+---+-t-+---lt;);~~'N!!"j,,_xci"r~,~_=:J;
I
,,,
Ls.o,,,
SYNC SELECT
CONTROL
~l
1
---.-_:_
I
I
I
rr
~
:°'-i.,.I '0---1----t--t-+---t--t---i-i
I
~
I
I
--,---,-....~'",.,. n: 'o--j.----t"--t--,
I
,cil"II
I
I
I
I
814
A,5
B15
A,6
B16
A,7·
B17
Al8
s,s
Al9
919,
A20:
B,q
A?I'
821
LOCAL/REMOTE
AUT0!88W
~
COMP. O'JT
A/8 R
T SW
A/8 L
+12v
tlZV
12,
B'B·/:;) J CABLE !r-+?-·V---;,---,-1
1
"" co•e I _l . I
HOOK UP
I
l
A?
82
GNC,
GNG
~
I
"/ c;3 I cvso, #
f_J FREO
----
# rRV601
·~V6C2 GAIN
rREO
B
• (SYNC SELECT'-)
~
SYNC SEP
---------------------------
3-2
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