6-17
6.9 RF Output Assembly/Components
[A10]
The RF Output of the System 7500™ is essen-
tially the secondary of three different output trans
-
formers, with only one of them actually located on
the RF Output Assembly. When troubleshooting
this assembly, caution must be taken on power set
-
tings and test leads connected, as voltage levels are
rated in the thousands.
Refer to the schematic (Figure C-18) and locate
T3 primary. The connections labeled P2-1 and
P2-2 connect to the Full Bridge Amplifier at
J2-1 and J2-3. The reactive components on the
secondary (C1 thru C7, L1 and L2) make up
a bandpass filter that is calibrated for 461KHz.
Following the filter are two transformers, T1 &
T2. T1 is a current sense transformer with a 1:7
turns ratio. T2 is a voltage sense transformer with
a 100:1 turns ratio. These transformers connect
to the Power Control Assembly for output voltage
and current monitoring (V
SN and ISN). Relays
K1 and K3 are normally open, and close any time
Cut, Blend, Pinpoint or Bipolar modes are activat
-
ed. These relays switch the Full Bridge Amplifier
Modes to the RF Output jacks.
Locate on the schematic the transformer labeled
Spray Output. This transformer is actually
mounted to the chassis and can be identified by
the color, which is black. The primary of this
transformer is connected to the HS/A.R.M.
Assembly (A11) along with the primary of the
ABC™ transformer. The ABC™ transformer is
mounted to the chassis and can be identified by
the yellow color. Relays K2 & K4 are normally
open, and close anytime Spray mode is activated.
These relays switch the Spray mode to the RF
Output jacks.
On the outputs of K1-K4 is a transformer, T4,
called a Balun. It has an additional winding called
Balun sensing. A balun transformer helps mini
-
mize RF leakage during open circuit conditions.
During “balanced” conditions, all the RF current
leaving the RF amplifier exits and returns through
the balun transformer. Under this ideal condi
-
tion, the magnetic fields within the balun created
by the RF currents are equal and opposite. When
the fields are equal and opposite, the net magnetic
field is zero resulting in zero impedance presented
to the RF output current.
If alternate current paths exist, some of the cur
-
rent exiting through the balun is returned to the
amplifier via an alternate path. In this condition,
the fields of the balun are not equal, presenting
some degree of inductive impedance to the output
current, limiting available alternate path leakage
current. The impedance caused by the unbalanced
current develops a magnetic field that is now
greater than zero within the balun transformer,
allowing for a single-turn winding that will sense
the leakage.
The magnetic field caused by RF leakage currents
can develop a voltage that is proportional to the
amount of leakage currents. With a balanced field
within the balun, the sense winding has zero volts,
and as the leakage increases, the voltage on the
sense winding increases, allowing a circuit to be
employed into the System 7500™ that will reduce
output voltage when RF leakage is sensed.
Each output of the system is discrete, or has an
output relay with the exception of ABC™ Active.
The active outputs are H1RF (handcontrol 1),
H2RF (handcontrol 2), FTRF (footcontrol), and
BPRF+H (Bipolar). In addition to the active
outputs are the Patient Return which have three
relays for isolation. K9 is closed only when
ABC™ is activated to provide a return path back
to the ABC™ output transformer. K8 is closed
when Cut, Blend, Pinpoint or Spray is activated,
and K11 is closed only when Bipolar is activated.
The table below identifies which relays are closed
for each of the modes activated.
Mode/Output Relays Selected
Cut, Blend, Pinpoint (H1RF) K5, K8, K3, K1
Cut, Blend, Pinpoint (H2RF) K7, K8, K3, K1
Cut, Blend, Pinpoint (FTRF) K6, K8, K3, K1
Bipolar K10, K11, K3, K1
Spray (H1RF) K5, K8, K2, K4
Spray (H2RF) K7, K8, K2, K4
Spray (FTRF) K6, K8, K2, K4
ABC K9
The A.R.M. connector is also located on the RF
Output Assembly, however the A.R.M. circuit is
on the HS/A.R.M. Assembly and will be cov
-
ered in that discussion. A failure due to a relay
will obviously appear as low or zero RF Output
Power. Finding the bad relay is not always obvi
-
ous, but when troubleshooting potential relay
problems, start with the driver. The relay driver is
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