Circuit; Interface Circuit; Video Interface - NEC MultiSync 3D JC-1404HME Service Manual

(2-2-3) H.V. circuit
The H.V. circuit supplies high voltage (23.5 kV) to the anode of the CRT. This circuit is composed
of the fly-back transformer and the H. out circuit. The energy is stopped on the primary coil of
F.B.T. when the H. output transistor 0523 is turned ON. This energy is transformed through the
F.B.T. when it is turned OFF. The high voltage generated by the secondary coil is rectified 23.5 kV.
This voltage is controlled by VR504. The high voltage circuit has two high voltage protection
circuits to meet the D.H.H.S. standards.
The first circuit is IC401 's (HA 11423) internal protection circuit. If the high voltage increase, the
voltage at TP2005 increase. When TP2005 voltage exceeds 0. 7V, IC401 's protection circuit turns
ON and the H. OSC. is stopped.
The second circuit's operation is similar to the one described.
(2-3) Interface Circuit (PWE-250)
(2-3-1) Video Interface Circuit
RELAY
,------,
I I
I I
ANALOG
I
_V_I_D_E_O_I_N_P_U_T _ _ _ _ .,...:
0 -
I
TTL
I
I
TTL
DECORDER
ICB01
D/A
CONVERTOR
OUTPUT
BUFFER
CN-A 11 pin
CONTRAST
CONTROL
TTL/ANALOG
ID CIRCUIT
TTL INPUT H. SYNC.
ANALOG INPUT NO USE
8.5V SERIES
REGULATOR
TTL ENABLE (OUTPUT 8.5V)
ANALOG DISABLE (OUTPUT 0V)
(Fig. 2-3-1) BLOCK DIAGRAM of the Video Interface
• TTL/ANALOG identification circuit
CRT
PWB
This circuit monitors the signal on pin 11 of CN-A. If there is a Horizontal pulse, the MS 30 assume
that TTL Video is connected to it. The TTL/ANALOG ID output controls relays RL801 and
R L802 and the 8.5V series regulator.
In case of ANALOG video input, the relays enable the ANALOG circuit and the 8.5V line, and
disables the TTL enable circuit.
In case of TTL video input, the relays enable the TTL circuit, the video information is passed to the
TTL decoder (IC801 ). This TTL decoder IC produces signals based on the MODE and color switch
settings.
The maximum output of the O/A converter is 0.7 Vp-p.
The output level of the O/A converter is controlled by the CONTRAST VR only when a TTL
video signal is the video source.
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