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Model 5501A
Theory of Operation
Assembly test gate, inhibiting the gate. This disabled gate prevents a set signal (generated during time t,)
from reaching the fault latch. As a result, the fault latch remains cleared and provides a low enable signal to
the clear gate. During time t, (approximately gseconds after theretunecyclestarted), a 10-microsecond CLR
signal i s inverted by the enabled clear gate and the resulting CLR trigger clears the tune latch.
3-38. If the retuning process i s not successfully accomplished, the threshold detector output (on the Lock
Reference Assembly) remains low. This signal prevents generation of asystem reference signal and provides
a false (high) R E F OK signal. This high signal enables the test gate (on thecontrol Assembly) during times t,to
t,. As a result, the t,signal (from the retune timing circuits) drives the test gateoutput low. This low signal sets
the tune fault latch. The set latch:
a.
Provides drive to light the RETUNE FAILURE LED indicator.
b. Inhibits the clear gate; thereby keeping the tune latch set. As a result the RETUNE LED indicator
remains ON.
c.
Maintains an active (high) ERROR output signal.
3-39.
DIAGNOSTIC SIGNALS AND INDICATORS. Improper laser current, PZT voltage or beam sampling
inputs results in an active (high) diagnostic ERROR output signal. The laser cathode resistor on the
Connector Board provides an input voltage which serves as a monitoring signal to the Control Board Laser
Current Fault Detector. This fault detector is a dual comparator which i s activated when the monitoring
voltage (representing laser current) exceeds an upper limit of +2.0volts, or falls below the lower limit of +1.0
volt. The resulting low LI FAULT signal activates the error gate, turns the LASER CURRENTfault indicator on,
and provides a subsystem LASER CURRENT fault diagnostic output signal.
3-40. A part of the PZT Power Supply output voltage (approximately 1/1000th) i s sampled and applied to the
PZT fault detector on the Control Assembly. Thiscircuit is also a dual comparator which is activated when the
PZT sample input exceeds +1.8 volts, or falls below $0.27 volt. A low
P X
output signal sets the tune latch
activating the ERROR diagnostic output signal. In addition, the set tune latch output lights the RETUNE
indicator and provides an active RETUNE diagnostic output signal. This signal indicates a laser retune
requirement.
Figure
3-7.
Retune Timirig Diagram
To 1 "
DEPRESSED1
T1 IS1 RELEASED)
Tz
T3
RETUNE CMD
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RETUNE
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RETUNE
TIMING
TEST GATE IT21
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3.0 SEC
CIRCUITS
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CLR IT31
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10.0 WSEC
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