Circuit Description; Power Circuit; Video Amplifier Circuit; Control Board - Panasonic WV-BM90 Service Manual

CIRCUIT DESCRIPTION

1.
Main Board
l - l
This circuit generates the regulated + 5V DC, + 12V DC and
+ 24V DC from 22OV/240 AC.

1-2 Video Amplifier Circuit

The composite video signal fed to base of 46 from control
board through pin of CN3.
The video signal from the emitter of 96
(CONTRAST), amplifier Q7,Q8 and Q9 to cathode of CRT.
1-3 H.V Deflection Circuit
This circuit generates vertical (V) deflectlon sawthooth
current for V scanning of the beam inside the cathode ray
tube (CRT) and horizontal (H) deflection sawthooth current
for horizontal scanning of the beam inside the cathode ray
tube.
1-4 High Voltage Circuit
(CRT) electrodes.
The flyback pulse generated by horizontal (H) deflection
circuit is supplied to the primary winding of the flyback
transformer (FBT) in high voltage pack T3 to step up the
obtained at the secondary winding of the transformer are
rectified to generate high voltages.

2. Control Board

2-1 Camera Power Circuit
The video monitor WV-EM90 has four camera power circuit
which supply the DC power to the specified cameras through
the coaxial cable respectively. Since these four circuits are
exactly same, the power supply circuit for camera-l will be
described.
This circuit consists of a constant current circuit, and a
In order to compensate the difference of voltage drop due to
the coaxial cable length between the video monitor and
camera, this circuit applies the constant current to the camera
regardlessof coaxial cable length.
+ 24V DC supplied from Main board through at pin 8 of El is
divided by zener diode D2, VRl (DC CURRENT ADJ) and R3 -
fed through VR8
IS
amplifier ICl (a) to base of impedance converter 471 for
controlling the camera DC power to steady state.
The variation of load current due to coaxial cable length is
detected by R6 and R7 as a voltage change and the changed
voltage is supplied to operation amplifier ICl (a) which
compensates the voltage differences between pins 2 and 3 of
fed to detecting resistors R6 and R7 is kept constant and the
constant current is supplied to the camera.
l
The video signal from the camera is multiplexed on the
power line, the rnisconnection protection circuit protects the
power circuit from a open or short circuit.
When the power switch on the video monitor is turned ON,
of Ql issupplied to pin 2 of operation amplifier ICl
At this time, approx. + 22V DC set from + 24V DC by dividing
with D2, VRl and R3 - R5 and supphed to pin 3 of ICI (a) is
compared with the potential at pin 2 so that the output at
pin 1 of ICl supplied to base of impedance converter 471 is
high level and Q71 is kept OFF.
At the same time, 43 is turned ON momentarily and approx.
and Dl to the camera. In the camera, approx. 40KHz pulse is
generated by the +4V DC and multiplexed on the power line.
This pulse is supplied to Q2 for turning it ON and Q? OFF.
Due to Ql OFF, collector potential is increased and thus the
output of (a) is decreased therefore, the impedance
converter 471 is turned ON and converts the impedance of
power line from high to low. As a result, the DC power is
supplied from the constant current circuit continuously
through 471.
While camera power circuit supplies constant current to the
camera, voltage difference appears at both end of R6 and R7
so that the Ql is turned ON and Ql(CONTROL SUB BOARD) is
kept OFF.
If this video monitor is connected to other CCTV cameras or
products, no pulse is fed back to the starter circuit and Ql
(CONTROL SUB BOARD) is kept ON. Therefore, no DC power
is supplied to the connected products in order to protect
them.
When the coaxial cable is disconnected in the operating
condition, no current is fed through R6 and R7, voltage drop
of R6 and R7 reduces and Ql is turned OFF. As a result, Ql on
the Control sub board is turned ON and potential at pin 2 of
turned OFF. In this way, the no DC power is supplied to the
power line.
(a).