Studio Technologies 76 V.1.10 - Manual (Page 33)

Model 76/77 User Guide Issue 7, August 2012
Studio Technologies, Inc. Page 33
for Surround
outputs. After the DC voltages are recog-
nized as valid, a short delay takes place
before the relays are allowed to function
normally. Whenever the AC mains input
drops below its nominal operating volt-
age range, the DC “rails” will drop and the
relays will almost immediately go into their
muted state. During testing it was found
that upon AC mains power up the monitor
outputs remained very quiet; during power
down a small to moderate “tick” was the
worst that was heard.
Model 76 to Model 77
Connections
Figure 6 gives a detailed description of
the signals that connect the Model 76
Central Controller to the one or more
Model 77 Control Consoles. The Model
76 provides a 12 volt DC, 200 milliampere
maximum power source for use by one
or two Model 77 units. The DC output is
current-limited to minimize the chance
that a short-circuit condition will damage
the Model 76’s circuitry. An asynchronous,
bi-directional data interface links the
units. This uses an RS-485 hardware
connection scheme that operates at a
rate of 115.2 kbit/s and uses an 8-N-1
data format. The Model 76 communicates
with each Model 77 20 times-per-second,
receiving button and rotary level control
information and sending LED and 4-digit
display status data.
Mono-to-Center Polarity
It’s worthwhile to note that a polarity inver-
sion takes place whenever the stereo to
mono downmix function is active; the left
(L) and right (R) input signals experience
a 180-degree inversion in the Model 76’s
combining circuitry. This should not cause
a problem as monitoring audio signals over
a single loudspeaker is considered polarity
insensitive. Only during electrical testing
would this condition be detected.
Power-Up Messages and
Error Codes
Upon mains power being applied to the
Model 76 all connected Model 77 units
will go through a power-up sequence.
The sequence starts by each of the indi-
vidual LEDs lighting in a “walk-through”
sequence. At the same time the 4-digit
display tests all its LED segments. Then,
a set of messages provide details on the
specific Model 77 and connected Model 76
software versions:
1. Displays 77
2. Displays Model 77’s software version
3. Displays Model 77’s unit address
(A1, A2, A3, or A4)
4. Displays 76
5. Displays Model 76’s software version
After a successful system power-up
sequence normal operation will then com-
mence. Should a problem be encountered
during power up an error code may show
on the Model 77’s 4-digit display. If Err1
displays it indicates that communication
is not taking place with the Model 76. The
most likely cause would be incorrect wir-
ing of the data pair linking the two units.
This could be caused by one or both of the
wires being open (not connected) or the
data pair being reversed.