Ecler PAM1400, Service Manual

Page: 17 / 183

14
GENERAL RESET CIRCUIT (TURN OFF/TURN ON)
TURN OFF RESET. This circuit starts working when the AC current from the transformer secondary
disappears or, what is the same, when we turn the power amplifier off by pushing the power off switch, actually
disconnecting it from mains.
Circuit operation: The AC signal present at the anode D321 is rectified by this, attenuated and filtered by R13,
R348, R347 and C322, apllying it to the base of Q306, which is conducting into saturation and, as a consequence,
Q305 is cut. When this signal disappears Q306 is cut and then Q305 has its base feeded through R345, R346 and
R14 from the +V power supply, which has begun to lose voltage -because we have just cut the mains- but, because of
the high capacity value of the filter condensers, there is enough time to saturate Q305, which puts the resistances R15
and R344 (50
Ω ) in parallel with the power supply (+10V) of the logic circuitry, completely discharging the capacities of
the circuit, leaving it ready for a new reset pulse -the connection one-, what warranties the new turn-on, even with very
short time intervals (.1s) between turn-off and connection pulses.
CONNECTION RESET
This is made of C315, R336 and D314. It is the classical reset circuit, used in lots of applications.
In the exact connection moment the condenser C315 is not charged, with a high amount of current circulating
through it, or a high voltage in R336. This current decreases as the condenser is charging until it disappears. At the
same time, the voltage -in the extremes- of the resistance goes from maximal, in the beginning, to 0V. This way we get
a pulse whose duration depends on the time constant RC. The aim of the diode D314 is a fast discharging of C315
during disconnection.