Dc Voltage Detector; Overload Detection - Pioneer SX-3900 Service Manual

l c ( H A 1 2 0 1 0 )
F i g . 4 - 1 3 S i g n a l I n d i c a t o r C i r c u i t
abruptly decay, and Q5 will conduct owing to the
residui
component of +B. As a result, C4 will
rapidly discharge, Q6 will cease to conduct, where-
upon the relay will become de-energized and
restore muting.
DC Voltage Detector
The output circuit is connected to the Q3 emit-
ter and qa trase via a low-pass filter (R5, C2)'
Any DC voltages appearing the output circuit of
the power amplifier, it will be applied to the Q3
emitter and Q4 base. If the voltage is positive, Q4
turns on. C4 will rapidly discharge' If the voltage
is negative, QB tums on' C4 will rapidly discharge'
As consequence, Q6 will turn off and the relay
will become de-energized, thus causing the output
circuit to oPen.
Overload Detection
The overload detector circuit incorporates the
load (RL) in one side of a Wheatstone bridge (see
Fig. 4-15). The base and emitter of a sensing
tra'nsistor (Q2) are connected to the opposite
corners of ttre bridge, so if RL decreases, Q2 will
become forward biased. If RL falls below a
pre-
scribed value, Q2 will turn on' C4 will rapidly
discharge. As consequence, Q6 will tum off and
the relay will become de-energized, thus causing
the output circuit to oPen.
F i g . 4 - 1 5 O v e r l o a d D e t e c t o r
F i q . 4 - 1 4 P r o t e c t i o n C i r c u i t