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Power Supply Board:

This board contains a set of voltage stabilizers. TL431 ICs gives reference voltage to OPA548 power operational amplifiers. They are to support proper +23V, +5V separate for analog and digital circuts and simetrical +-15V for opamps in signal path. Separate transformer wireing are used for each voltage supply. The sixth wireing supplies VFD display through the DT138 triac.

OPA548 power supply

Each OPA541 has current limiter resistor and all of them except that one that feeds controller board have special line that through open collector inverters signal power fail or get power down status from controller. In case of negative voltage stabilizer the sutdown line is more complicated due to it is refered to negative rail. The transistor circut on the top of power supply board schematic is to controll voltage level on the secondary wireing of transformer. On the power fail condition mute relay are immedialty shut down to avoid hurting the speakers and PFAIL line tells controller to store settings and shut down the whole device.

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