Logitek BRIGHT-VU, Руководство по эксплуатации и обслуживанию

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Two channel audio data is fed synchronously
(data,clock,frame sync) to serial ports on the DSP via
input connectors P1 and P2. If the control card is only
driving one display then the DSP IC4 will only have
one serial port which will be connected to P1. In this
case only left side connectors P1 and P6 will be active.
4-6 Analog Input Card
The audio from the left input XLR connector J1 is
connected to a RF lowpass filter formed by R1, R2, C1
and C2. The resistors also form a -9 dB pad with the in-
put impedance of balanced receiver IC1. IC1 provides
an additional -6 dB pad between its input and output.
These pads allow +20 dBu input signals to be handled
by the +/- 5 volt supply rails. Signal gain is adjusted via
trimpot R7 which is the feedback resistor around gain
stage IC3a.
Signal from IC3a is fed through anti-alias filter R9,
C5 and DC isolated by C8 before connecting to the left
input of the sigma delta analog to digital converter.
Right channel connects to the converter via similar cir-
cuitry.
The 12.288 MHZ master clock input to the ADC is
generated by a crystal oscillator located on the DSP
control card. Combined left and right audio data is
sent synchronously (data, clock, frame sync) to the
DSP in 64-bit strings via connector P3.
IC5 and IC6 supply low noise reg/- 5 VDC to
the analog portions of the circuit. The digital part of the
data converter gets its +5 VDC from the DSP control
card.
4-7 Digital Input Card
Serial digital audio in the AES/EBU or S/PDIF for-
mat enters the card via XLR connector J1 and is di-
rectly connected to the output connector P2. Note that
no buffering is applied to the loop through output.
The input data signal is connected to pulse trans-
former T1 via DC blocking capacitor C2. The output of
T1 is loaded with R1, R2 or R3, depending on the load
required, and connected to data receiver IC1. C1 and
R4 from a loop filter used by IC1 to recover the embed-
ded clock from the coded input signal. IC1 separates
the audio data, channel data and clock from the input
signal. The audio is sent to the DSP in 64-bit strings
via connector P3.
IC2 creates a low noise +5VDC for use by the ana-
log front end of IC1. The voltage is stabilized by C6 &
C3 and is clamped against over or reverse voltage by
D1.
4-8 LED Display Card
Reg5 VDC from J1 is stabilized by C1, C2
and connected to LED display driver IC1. IC1 controls
the 40 display LEDs by scanning them in a six by eight
matrix. Segment lines are current controlled and con-
nected to the LED anodes. Digit lines connect to the
LED cathodes. Scanning is accomplished by taking
each digit line low one at a time and sourcing current
from the segment lines for whichever of the 8 LEDs in
a digit group need to be lit.
The display driver accepts synchronous serial data
(clock, data, load) from the DSP on the control card in
16 bit strings composed of an address byte and a data
byte. About once a second the DSP sends a complete
set of setup codes for the display driver. If the display
card is plugged in while the meter is running, it will re-
main blank for a moment until these codes are re-
ceived.
4-9 Power Supply
Each Bright-VU contains a ground isolated and fil-
tered step-down power supply to create the necessary
operating voltages. This supply is located on a PCB on
the right side of the meter enclosure.
Mains AC from the power entry module J2 is fed
through fuse F1, located in a drawer under the power
cord in J2, to J1 on supply card LG-253. J1 feeds volt-
age selection switch S1 which connects the dual pri-
maries of transformer T1 in series for 230 VAC
operation or parallel for 115VAC operation. The dual
secondaries of T1 are wired in parallel and loaded with
a full-wave bridge rectifier RT1. The DC output of RT1
is filtered by capacitors C1 and C2 and fed to the red
and green output pads. The voltage should be be-
tween 8 to 10 VDC with less than .5 volt of ripple.
Analog input models will also have a charge pump
consisting of IC1 and C3 that feeds filter C4 and the
black output pads. The voltage should be -8 to -10
VDC with less than .2 volt of ripple.
Jumpers soldered to the output pads feed power to
one or two DSP control cards.
* * * * * * * * * * WARNING * * * * * * * * *
Dangerous voltages from the AC mains are present
on the bottom of the power supply card. Always dis-
connect the AC power cord when servicing this circuit
board. Always completely reinstall this board before
reconnecting the power cord.
* * * * * * * * * * * * * * * * * * * * * * * * * * *
4-10 ADC Input Card
The audio from the left input 1/4" phone connector
J2 is connected to a RF lowpass filter formed by R10,
R11, C3 and C4. The resistors also form a -9 dB pad
with the input impedance of the balanced receiver IC4.
IC4 provides an additional -6 dB pad between its input
and output. These pads allow +20 dBu input signals to
be handled by the +/- 5 volt supply rails. The output of
IC4 is unity gain inverted by op-amp IC2b and fed back
to the reference input of IC4. This enables IC4 to pres-
ent an identical resistive load on its two input pins. In-
put gain is adjusted via trimpot R9 which is the
feedback resistor around gain stage IC1b.
** Bright-VU Instruction Manual ** Page 9