2. Trouble symptom.
The first indication of trouble in a particular
circuit shows up in the operation of the equipment. The trouble can be due
to improper operation of the equipment, an actual malfunction within the
equipment, or conditions outside the radar. Your job is to determine which
of these conditions is causing the trouble.
Therefore, you must know how
the equipment works and what the indications are for normal operation. For
example, the radar operator complains: "No signals on the indicator, but
receiver grass (noise) is normal."
First, check the settings of operator
controls. Perhaps the radar operator is at fault. Next, check for proper
meter readings, switch positions, panel lamps, and other devices built into
the equipment. Knowing what each control does and what each meter or lamp
indicates, helps you to troubleshoot quickly and efficiently.
a. Sectionalization. Once you have verified the symptom, the next step
is to analyze and evaluate the trouble symptom to decide which section of
the radar is giving trouble.
Here is where your knowledge of equipment
operation is important.
For example, suppose during verification of the
trouble symptom, you see that the magnetron-current meter reads zero. You
know immediately that the trouble is in the transmitting system. You also
know that the timer, receiver, and indicator systems are operating properly
because there is a sweep with normal receiver grass on the indicator. There
is an input to the transmitting system, but no output.
Thus, you have
sectionalized the trouble to the transmitting system just on the basis of
your knowledge of the equipment.
b. Localization. The next step is to localize the fault to either the
magnetron or modulator. Once again, check the meters and indicating lamps
to decide which stage is at fault.
Suppose the reverse-current meter
reading is zero, but the high-voltage meter reading is higher than normal.
These meter indications show that the modulator is not working.
The
THYRATRON is not loading the power supply and a pulse is not being developed
to cause reverse current to flow. Now is the time to use a schematic and
test equipment such as a synchroscope. Check for the modulator output pulse
at the test jack provided for this purpose.
If there is no modulator
output, then you have localized the trouble to the modulator.
c. Isolation.
Isolating the faulty component is the easiest step of
all because there are so few components to check in the high-level
modulator. Use the schematic diagram and voltage and resistance charts to
isolate the faulty component quickly. But first make a visual check of the
modulator. Check for lighted filaments in the THYRATRON,
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