Ecler PAM4100, Service Manual

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This delay time is achieved by using a RC cell, where R135=287K and
C119=47mF/50V. As this cell charges, its voltage increases untill reaching the 40106-
type Schmidt trigger (IC108) switching value; at this point, the relay opens and the
amplifier starts to function normally.
The discharge or reset of capacitor C119=47mF can be done by cutting off the power
supply, or by triggering the Thermal or other protections. During a short period of time,
BC817-type transistor Q102 acts like a switch, shunting two 750 ohm resistors to
C119.
Moreover, the amplifier includes some other additional features, like:
· Volume control by a VCA system.
· An ANTICLIP system.
· A Temperature control system.
The ANTICLIP system. When the amplifier reaches clipping levels, the operational
amplifier looses control on the system's performance and at its output some ±Vcc
voltage peaking pulses may appear, proceeding from its power supply. This peaking
pulses are used to be rectified and sent to an optocoupler (IC111), wich varies the
system's VCA control voltage as a function of those pulse's amplitude, creating a
negative feedback wich should pull back the system into stable functioning area.
The Temperature control system has three main functions:
· Controlling the cooling fan speed, as it is a function of the measured temperature. The
fan's operation voltage range is »7 to 4 Volt.
· Suspending the amplifier's functioning when the temperature exceeds »92ºC
· Reducing the amount of power output, depending on the module's temperature (as it
rises above 85ºC) and on the main power supply's transformer (above 120ºC).
The temperature control system consists on two LM35D-type IC's, wich act like a
thermal probe; one is placed on the amplifier's heat sink, and the other is placed into
the main power supply transformer's core. Moreover, three amplifiers, a comparator
for the thermal probe and a 7805-type IC to feed the cooling fan are used.
The first amplifier (1/4 IC114) acts on the cooling fan speed control. The second
amplifier (1/4 IC114) modifies the VCA gain control, in order to reduce the system's
gain if the temperature rises above 85ºC. The third amplifier (1/4 IC114) modifies the
VCA gain control, in order to reduce the system's gain if the temperature rises above
120ºC. The comparator (1/4 IC114) is responsible for the output shutdown relay
performance, in order to close it as the temperature reaches 92ºC, and thus cutting of
the amplifier's MosFETs bias current. As this happens, the signal output of the whole
unit is cutted off.
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