Q2 OPERATION AND MAINTENANCE MANUAL 9601 71
ON/CUT CIRCUIT
The ON circuit of an input module is based around IC11 a dual,
positive edge triggered S/R Flip Flop. Under static conditions C40
will charge through R140 holding the clock input low. Pressing the
ON switch applies Vdd to the clock input causing pin 2 to be
clocked through to pin 1 reversing the states of Q and Q bar. For
the channel to be on Q bar should be high. Assuming that the
channel is SAFE at the moment then pin 10 of IC12 will go low
causing pin 11 to go high. Following this through the ON LAMP
link TR3 will be switched off by this high causing TR5 to be off
which means that the LED will be ON. An anti phase feed is taken
to the series and shunt FETs such that in the ON condition the
series FET receives a high while the shunt FET receives a low.
An alternative is for the lamp to indicate the CUT condition. A
local channel CUT will set Q bar low and thus pin 10 of IC12 will
be high. This will cross the cut lamp link and switch TR3 off
causing the LED to come on indicating a mute. At this time Q is
high causing pin 4 of IC13 to be low and therefore pin 6 of IC12 to
be low. If the channel is not locally cut but an external cut is
received from one of the master cut switches Q will be low and the
external cut signal will put a low on to pin 6 of IC13. Pin 4 will
thus go high and allow the FLASH signal to blink the CUT lamp if
LK9 is installed. The external cut is also applied to pin 8 of IC12
causing pin 10 to go high to operate the FETs and the lamp. Thus a
flashing cut lamp is an indication that a remote cut has been
received.