Covidien Force FX, Service Manual

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Footswitch Board
4-16
Force FX Electrosurgical Generator C Service Manual
• When COM2 is selected, the Cut and Coag mode select switches are read.
To read the switches, the main microcontroller asserts the desired BANK select line and
reads the state of the keyboard switch return lines KBD_D0 through KBD_D7. These lines
are read through port A of FPGA U16-D and Voltage Translator U20 on the Control
Board.
Footswitch Board
Refer to Chapter 9,
Service Parts
, for components and the
Schematics Supplement
for
board drawings and schematics.
The Footswitch board is mounted inside the rear panel. It contains circuitry accepting and
decoding footswitch keying inputs and an audio circuit for announcing generator keying
and various alarm tones. The Footswitch board interfaces with the Power Supply/RF
board.
Footswitch Decode Circuit
Two monopolar footswitch connectors and a bipolar footswitch connector are mounted
on the Footswitch board and extend through the rear panel. The monopolar footswitch
connectors (J3 and J2) accept monopolar footswitches and provide footswitching
capability for the Monopolar 1/CEM and Monopolar 2 Instrument receptacles located on
the front panel. Use only a Valleylab monopolar footswitch with the Force FX
Electrosurgical Generator C.
Use of an incompatible footswitch may cause unexpected output. The bipolar footswitch
connector (J4) accepts a bipolar footswitch and provides footswitching capability for the
Bipolar Instrument receptacle on the front panel. Capacitors C39–C46 provide filtering
that blocks high frequency noise from exiting the generator on the footswitch cables.
As required by the IEC, the footswitch circuit is isolated from patient connected and
ground referenced circuits and is able to withstand a potential of 500 V
rms
(50/60 Hz). To
obtain this isolation, the footswitch connected circuitry is powered from an isolated
power supply (U2). The isolated power supply, a MER1S1212SC, operates from the
ground refe12 V power supply and supplies an isolated 12 V.
Resistors R18 and R19 form a voltage divider that yields a signal (V
ref2
) of approximately
6 V. This reference voltage is applied to the noninverting inputs of comparators U3A,
U3B, U4A, U4B, and U5A.
The common terminal of each footswitch is connected to the +12 V isolated power
source. Footswitch activation causes this voltage to be applied to a resistor divider. The
values of the resistors comprising the input divider are selected to provide a switching
threshold of approximately 750 Ω.
The divided voltage is then applied to the inverting input of one of the five comparators.
When the voltage at the inverting input exceeds the voltage at the noninverting input,
the open collector output of the comparator turns on, causing current to flow in the LED