Turn-On Delay; Output Relay Muting; Input Muting; Auxiliary Output Jack - Crown CE-1000A Service Manual

3.8.5 Turn-On Delay

U104-A provides a time delay after turn-on to let the
rails stabilize before connecting the load to the ampli-
fier output. The block diagram in Figure 3.2 shows that,
while the turn-on delay circuit is active, the amplifier is
in fault mode.

3.8.6 Output Relay Muting

The relay K100 is in series with the output of the ampli-
fier. The relay coil is connected to U104-A, U104-B
and U104-C; these inputs determine if the relay should
be open (disconnecting the load from the amplifier) or
closed. The fault conditions which drive the relay in-
puts are outlined in Figure 3.2 and listed here.
1. Heat sink exceeds thermal limit
2. Transformer exceeds thermal limit
3. A short has been applied to the
output
4. There is DC on the output
5. The turn-on timer has not released the
relay yet

3.8.7 Input Muting

The summed output from U104 -A,B,C is also used to
drive an inverter, U104-D, that mutes the input to the
error amplifier via Q133. Q133 is a FET, which can open
faster than the relay can. This saves the relay, K100,
from having to switch high currents which can erode
the contact surfaces.
Circuit Theory 3-6
CE Series Power Amplifier Service Manual

3.8.8 Auxiliary Output Jack

The auxiliary output jack allows for remote monitoring
of the amplifier's fault status. The concept of the aux-
iliary output jack is to short two pins of a common RJ-
11 connector (J5) together through a transistor any
time that the amplifier is operating normally. If the am-
plifier is off or in any fault condition, the two pins on
J5 will effectively be an open circuit.

3.9 Fan Control Circuitry

There are two different kinds of input to the fan speed
control. One is the heatsink temperature and the other
is the input from the transformer thermal switch. The
heatsink temperature is reported via U106, which is
thermally connected to the heaksink. The current from
U106 is delivered through R190 to develop a voltage
at the anode of D119. D119 is used as part of an OR
gate with channel 2 and with the transformer thermal
sense.
As the reported heatsink and/or transformer tempera-
ture rises, the Darlington transistors, Q1 and Q2, are
turned on harder. So, a thermally proportional volt-
age is supplied to the fan, allowing it to run faster as
the reported temperatures increase. However, if all of
the reported temperatures are below a set threshold
level, the transistors Q1 and Q2 will be biased off,
hence cutting off the supply voltage to the fan. This
results in lower power consumption and lower noise
levels during times of low-power operation.
Rev. D