REVISION C
BMX SERIES III CONSOLE
68
PACIFIC RESEARCH & ENGINEERING
channel Send potentiometers R43 and R44, and routed through Send relay K2 to the two Send circuit
ON/off switches. This module may be modified for post-pan stereo Send operation by following the
procedure outlined in Section 5.3.
LOGIC
The selection of the A or B input to the module results in the selection of the corresponding control logic.
One contact on input selector switch S2 is connected to pin 9 of U200, U201, U202 and U212. The set
of logic controls for input A are chosen when this line is low and the logic controls for input B are chosen
when this line is high. U200 and U201 select the A and B remote control inputs, U202 selects the status
of A and B programming switch S207, and U212 selects A and B tally output drivers.
Pressing the module’s ON button, or the On button on a remote control panel, causes the output of
U207A to go high and toggle flip-flop circuit U208 to the “on” state. The low output from pin 4 of the
flip-flop is connected to U206 pin 9, and U211 pins 12 and 8. If the logic programming switch has been
set for a microphone located in the Control Room, the output of U206 will turn on transistor Q200 to
pull down the Control Room mute bus. In the same manner U211D/Q201 and U211C/Q202 provide
Studio-1 and Studio-2 monitor muting for inputs set to those locations.
The high output from pin 3 of the flip-flop is connected to the inputs of U215B and U211B. The other
inputs of U215B are normally high; therefore, the high provided by the flip-flop will give a high output
to the tally lamp and audio relay drive circuits U213A/Q229 and U216B/Q228. The input to U216B
is delayed with a 40 millisecond network consisting of R273 and C237. Circuit U211B, used as an
inverter, along with U213B and Q230, removes the tally voltage from the OFF light. The outputs of
U213A and U213B also connect to U212, for routing to the appropriate remote tally lamp driver. Each
of the four tally outputs has its own lamp driver, shown schematically as Lamp Driver B, and each of
the two 12 volt output sources has its own driver, shown schematically as Lamp Driver A.
The lamp is driven by a low applied to R280, which pulls down the base of Q211 via conducting FET
Q210. Q210 normally operates at zero bias.
NOTE: If a short should occur in the load, Q210 will be pinched off to remove the base current from
Q211. This protection circuit is reset by switching off the drive and removing the short.
Pressing the OFF button on the module, or on the selected input’s remote control panel, will cause the
output of U214 to go high and toggle flip-flop circuit U208 to the “off” state. Time delay network R273,
C237, R274 is bypassed by CR209 to eliminate any delay in turning the audio relay off.
Operation of either the A or B input selector button places a momentary low pulse into the input of U214,
which will key the channel logic to the “off” state to prevent any input switching transient from being
routed into the console mix buses.
The CONSOLE COUGH ENABLE switch is intended for use with a microphone located at the console.
This switch connects the ON button directly to U215B to provide momentary channel muting whenever
the ON button is held depressed.