Valleylab Force FX-C - Power Supply;Rf Board

Power Supp/ylRF Board
When the ALARM signal is high, the UIC output transistor is turned on
while the output of VID floats. When the UIC output transistor is on, RIO
is pulled to ground and creates a fixed voltage divider with R32 to
produce the alarm volume level at the input to audio amplifier U7.
Meamvhile, the output of UID is allowed to f10at, thus removing the
variable resistor divider from the circuit. In this case, the volume control
potentiometer becomes a small resistance in series with the high
impedance input from the audio amplifier, negating the effect of the
volume setting.
Audio amplifier U7 and speaker SPI comprise the final stage in the audio
system. The audio signal is AC coupled to the amplifier by C25 to
eliminate the need for well-controlled input biasing. The voltage gain of
U7 is set to about 20 by floating its gain select pins. Because the VI output
signal is internally biased to Vcc/2, it is necessary to AC couple the
speaker through C27 to prevent the amplifier from DC biasing the
speaker.
Power Supply/RF Board
Force FXT/'l-C Service Manual
Refer to Section () for Components and the Schematics Supplement for
Board Dra\ving and Schematics.
The Power Supply /RF board is the main board of the generator. It
contains the high voltage power supply and the RF output stage. Other
functions performed by circuitry on this board include:
• Output voltage monitoring
• Output current monitoring
• Leakage current sensing (RF leakage sensing and reduction circuits)
• Spark control circuit
• REM impedance monitoring (REM circuit)
• Handswitch closure detection (IsoBloc circuit)
• RS-232 COImector
• Expansion connector
• EKG contact closure connector
• Output high voltage relays
• Temperature monitoring and fan control.
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