Covidien Force FX, Руководство по обслуживанию

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Power Supply/RF Board
4-18
Force FX Electrosurgical Generator C Service Manual
R32 determines the maximum audio volume and R11 determines the minimum audio
volume. R10 determines the audio alert volume level. R34 provides an alternate audio
signal path in the event of an open volume control potentiometer.
When the ALARM signal is high, the U1C output transistor is turned on while the output
of U1D floats. When the U1C output transistor is on, R10 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.
Meanwhile, the output of U1D is allowed to float, 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 SP1 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 U1 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
Refer to Chapter 9,
Service Parts
, for components and the
Schematics Supplement
for
board drawing 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. Circuitry on this board performs several
other functions:
• 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 TM circuit)
• RS-232 connector
• Expansion connector
• EKG contact closure connector
• Output high voltage relays
• Temperature monitoring and fan control