6-18
located on the Display Assembly, and one should
first verify that each relay according to the table
above is receiving a drive signal. Also, spend time
to test all modes and all outputs as the “process of
elimination” may be the fastest and most effective
way to identify a faulty relay.
6.10 Low Voltage Power Supply [A6]
This assembly provides 5V, 15V, and -15V to the
system circuits. A dedicated low voltage trans
-
former connects into the assembly at J1, where
it is tapped for 18Vrms and 8Vrms. The regula
-
tors of this assembly only require a rectified and
filtered input that is at least two volts greater than
the output voltage. The regulators have current
limit and thermal shutdown capabilities. A short
-
ed component on a different assembly can cause
excessive current draw from a regulator, that will
be limited, however the current draw will allow
the regulator temperature to heat up until the
thermal shut down is activated.
There are two (2) 15V regulators, with Q1 dedi
-
cated to the FB Amplifier and SE Amplifier RF
Drives. Q2 provides 15V for the system logic,
indicators and relays. Regulator Q5 provides the
-15V to the system to include the source for -10V
and -5V that is used on the display panel.
The 5V supply uses a small switcher type device
because the 5V supply current can be close to 2A.
A switcher operates more efficiently than a linear
regulator (such as Q1, Q2, & Q5), not needing
as much heat sink. As set up, the switcher oper
-
ates quite similar to the other regulators where the
input must be greater than the output for voltage
regulation to occur. The input to the switcher is
8Vrms and the output of the switcher is a square
wave at 5V. The LC (L1 & C10) components
convert the switching signal to a DC signal.
Included on this assembly is the flow control
pneumatic manifold. This manifold assembly has
the solenoid valve (one nearest front) and flow
control (proportioning valve) assembled within it,
and if one should fail, then both must be replaced.
The proportioning valve is current controlled so
as the current is increased, the internal opening is
increased allowing more argon gas to flow. The
solenoid valve is also referred to as a digital valve,
meaning it is either on or off.
To test the valve coils, place a DVM or oscillo
-
scope on the driver for the device under test. The
coil resistance of both valves is 72 ohms. The
proportioning valve voltage changes with the
flow setting (V=IR). The collector of the driver
for the digital valve will switch from 15V to near
ground when the valve is energized, as the valve
drops almost all of the voltage.
6.11 HS/A.R.M. Assembly [A11]
There are four independent and unrelated cir-
cuits on this Board Assembly. Each circuit will
be covered separately. The HS/A.R.M. assembly
is located near the front of the system and is the
top circuit board of the two that are stacked. (See
Figure C-20.)
6.11.1 Handsense Circuit
The Handsense circuit is comprised of three iso
-
lated Handcontrol circuits with each handcontrol
circuit dedicated to Monopolar Handcontrol
(handcontrol 1), Beam/Monopolar Handcontrol
(handcontrol 2), or Bipolar. Handcontrol
1 allows activation of either Cut or Coag.
Handcontrol 2 allows activation of either Cut,
Coag or ABC™. Bipolar allows activation of
bipolar when using hand activation forceps.
The components that provide electrical isolation
between the control circuits and the RF circuits
are T3 (continuity transformer) and U4-U8
(optoisolators). On the control side of the bar
-
rier, U3 (NE555 timer) provides a 100KHz drive
signal at a 20% duty cycle for T3 primary. The
secondary winding of T3 provides energy for the
handcontrol sense electronics on the high volt
-
age side of the isolation barrier. The bipolar
handswitch continuity detector will be used as an
example, since all sections are identical.
When the bipolar handswitch is closed, DC cur
-
rent flows through the LED of the opto-isolator,
U7. The LED produces a beam of light which
falls on the photo transistor in U7 causing it to
switch on and draw current. This current pulls
the signal line /HBP to a low voltage, and this
state is interpreted on the Display Assembly as a
switch closure. When the handswitch is released,
the LED goes dark causing the photo transistor
to cease conduction and allow the signal line to be
pulled high by a resistor network located on the
display PCB.
Handcontrol 1 and Handcontrol 2 sense circuits
operate in the same manner for Cut or Coag
requests. An exception, however, is an ABC™
activation sensed as a result of both Cut and Coag
photo transistors being in the ON state during
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