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Display Board
Each display driver (U6, U10, and U14) can drive up to eight banks of eight LEDs by
multiplexing the time that each bank is turned on. The banks can be wired together to
increase the time that a group of LEDs is on, effectively increasing the brightness of that
group.
U10 drives the discrete LEDs and the CEM LED. These include green indicators for the
bipolar modes (Precise, Standard, and Macro), the cut modes (Low, Pure, and Blend), and
the coag modes (Desiccate, Fulgurate, and Spray). The anode of the mode selection LEDs
are tied to driver U10. By using pairs of the driver digit lines, the duty ratio for these LEDs
is effectively 1/4.
U6 drives the seven-segment displays that indicate power settings. U4 and U5 indicate
the bipolar power setting, U7–U9 indicate the cut power setting, and U11–U13 indicate
the coag power setting. The anodes of these displays are each tied to only one digit line
of the driver. The effective duty cycle is 1/8 for each seven-segment display.
Some filtering components are associated with U6, U10, and U14. Bypass capacitors C3,
C4, C7, C8, C9, and C10 are connected between + 5V and DGND. C3, C4, and C10
have a relatively small capacitance value of 0.1 µF to filter higher frequency noise. C7,
C8, and C9 have a relatively large capacitance value of 47 µF to supply the large spikes of
current for the LEDs generated by the multiplexing action of the drivers, which typically
occurs at 250 Hz.
Resistor array R18 reduces the input impedance of the display driver inputs as seen by the
main microcontroller on the Control board. This rounds off the edges of these digital
signals, reducing high frequency emissions. The lowered impedance also reduces the
susceptibility of the circuit to noise from other circuits.
CEM Switch Circuit
When you plug a CUSA handpiece with a CEM nosecone into the Monopolar 1/CEM
Instrument receptacle, the small nonconductive pin in the plug pushes a spring-loaded
plastic lever arm mounted inside the front panel. This lever arm activates a small switch
that plugs into the Display board. The switch signal tells the microcontroller to limit the
power.
Mode Selection and Power Control Switches
The mode selection and power control switches are arranged in a matrix. The main
microcontroller selects a bank of switches to read by asserting a bank select signal
(BANK0, BANK1, and BANK2-labeled 413_PA6) through port A of the Dual Supply Bus
Transceiver with Configurable Voltage Translation SN74LVC16T245 (U31) and the FPGA
XC65LX9-3CSG225C (U16-D) on the Control Board. These signals are buffered by FETs
Q1, Q2, and Q3 respectively and become the switch drive signals COM0, COM1, AND
COM2.
• When COM0 is selected, the power control switches is read.
• When COM1 is selected, the Recall Switch and the Bipolar mode select switches are
read.
4-15
Force FX Electrosurgical Generator C Service Manual
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