Maintenance—Type 324
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High Impedance Voltm eter (10,000 ft/V DC or greater)
Ohmmeter; 1 1/2-V source supplying less than 2 mA of
current on the X 1 k scale.
Test oscilloscope (2 MHz bandwidth; 25 MHz bandwidth
for troubleshooting Vertical Am plifier high frequency prob
lems)
Transistor Curve Tracer or Transistor Tester
General Techniques
Proper troubleshooting logic is the most important tool
in equipment repair. The following guide provides a logical
sequence for analyzing equipment failures:
1. Check all external control settings.
2. Determine that operating procedure is correct.
3. Determine all of the trouble symptoms.
4. Perform a visual inspection.
5. Troubleshoot the circuitry; repair as necessary.
6. Check the calibration status; recalibrate as necessary.
Control Settings and Operating Procedures. Refer to the
Operating Instructions section to verify external control
settings and operating procedure.
Trouble Symptoms. A fter it is confirmed that trouble
exists, the response to all exterior controls should be ob
served. The first-time operation listed in Section 2 can be
used for this purpose. All trouble symptoms should be
evaluated and compared against each other. A good
example of this is power supply trouble, which will usually
cause problems in otherwise unrelated circuits.
Visual Inspection. In visually examining the Type 324
Oscilloscope, take special note of the area indicated by
evaluation of symptoms. Look for loose or broken connec
tions, improperly seated transistors, and burned or other
wise damage components. Repair all obviously defective
parts. Investigate the cause of heat damage to components.
Detailed Troubleshooting. If the trouble has not been
disclosed and corrected through the procedure outlined, a
detailed troubleshooting analysis must be performed. The
Circuit Description section, the Schematic Diagrams, the
Calibration Procedure, and the Troubleshooting aids con
tained in this section are designed to expedite trouble
shooting.
The Circuit Description Section provides a fundamental
understanding of circuit operation and is referenced to the
Schematic Diagrams. The Schematic Diagrams contain volt
age and resistance values and signal waveforms. All specified
operating conditions should be duplicated before making
voltage or waveform comparisons. In cases where the black
numbers and blue numbers on the schematics give con
flicting voltage values, the blue numbers should be used.
NOTE
Voltages and waveforms may vary slightly between
individual Type 324 Oscilloscopes and are also de
pendent upon the characteristics of the test equip
ment used to obtain them. Voltages and waveforms
given in the schematics should be checked against
each instrument while it is operating properly. Devia
tions should be noted on the schematics for later
reference.
Calibration. Although the calibration procedure is in
tended primarily for instrument calibration, it can serve as
an efficient troubleshooting aid. Since each step is based
upon satisfactory performance of the preceding steps, the
problem circuit will be encountered before circuits which
are dependent upon it.
Troubleshooting Basic Components
Transistors and Diodes. The quantity of semi-conductor
devices in the Type 324 Oscilloscope requires that anyone
working on it have a general knowledge of semi-conductor
operation. Some basic information is presented here to aid
in this respect.
Direct Replacement. Once a casualty has been isolated
to a specific circuit, the ease of replacing transistors often
makes substitution the fastest means of repair. Use the
following instructions if the replacement method is used:
Determine that the circuit is safe for the substitute
component.
Use only known-good substitutes.
Have only one transistor out of the instrument at a
time to avoid mixing them up.
Insert transistors properly, using Fig. 4-13 as a guide.
Check operation after each component is replaced,
and be sure to return good components to their original
sockets.
If the trouble is not corrected by this procedure, re
check the semi-conductors under operating conditions.
Check calibration after a bad component has been
replaced.
W A R N I N ^ J
Voltage, either positive or negative, is often present
on the cases of metal-cased transistors when the
oscilloscope is energized.
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