Sierra Video Manzanita 44VSCP - Manual (Page 6)

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Sierra Video Systems • P.O. Box 2462 • Grass Valley, CA 95945 • (530) 478-1000 • Fax (530) 478-1105
MODEL 44 INSTRUCTION MANUAL
Model 44CPW.
Video circuits. Each video input is AC coupled to
a wideband emitter follower (Q1). R1 connects to
a -0.7V DC reference, which compliments the DC
offset of Q1. The output of Q1 drives four cross-
point IC (U2), one for each of the four buses. U1
is a 200 MHz four input by one output crosspoint.
U1 includes a two line to four line control decoder.
The output of each four by one crosspoint bus is
connected to an identical output amplifier, U2. U2
is a 200MHz wide band video amplifier with a very
low output impedance (about 0.1 ohms). R9 in
conjunction with R8 plus variable resistor R7 sets
the gain of the entire Model 44 to 2X. R10 raises
the output impedance to 75 ohms required to inter-
face to external 75 ohm coax cable environment.
Pulse switching. Each of the four pulse inputs is
buffered by an emitter follower, Q2. In order to
handle the higher signal level needed to switch 4
V P-P sync, HCMOS IC switches, U3, are used.
The x2 gain output amplifier is based on a
250MHz op-amp, U4.
Control circuits. The control circuits for the
Model 44CPW are the same as the Models 44VS
and 44C except different component designators
are used. The processor is U7 and the diagnostic
LED is LED 1.
Power supply. 24VAC center tapped is produced
by an external power transformer. The low voltage
AC enters the module on J3 pins 27 and 28. It is
rectified by D3 through D6. C22 and C23 are the
positive and negative primary filters respectively.
U8 produces +5V for the input buffers and video
crosspoints. U10 produces -5V for the input
buffers and video crosspoints. U9 produces +5V
for the video output amplifiers and the processor.
U11 produces -5V for the video output amplifiers.
U12 produces -12V for the pulse output amplifiers.
Control panel.
503151 control panel. The 503151 is a 16 switch
circuit board which uses LED lamps and includes
switch encoding and lamp driver circuits. The
503151 is primarily used with the Model 44 4 by
4 video plus stereo audio switcher and the Model
44C component video router.
Refer to the schematic diagram while reading the
following circuit description. The 16 switches are
connected together in a 4 by 4 matrix configura-
tion. This allows U1, a keypad encoder, to be used
to convert the one-of-sixteen to a four bit binary
code. U1 also provides switch debounce and key
rollover, which means that if two buttons are both
selected, only the first switch detected is encoded
until all switches are released. The output of UI
drives a two channel one in by four output data
switch U2. U2 converts the output of U1 to select
the “A” and “B” select lines for only the desired bus.
The other three bus select outputs of the 503151
remain in a high impedance state. The latching
circuit on the 4 by 4 switching module (the other
end of the system), is a 23K ohm source impedance.
The lamp circuit of the 503151 consists of U3 and
U4, dual two line to four line decoders. R11, R12,
R13, and R14 limit the current in the LED’s to
about 20MA.
The 503151 is powered with unregulated DC. U5
produces regulated +5V.