TM 11-6625-1633-45
the defective part by voltage measurements or resistance
measurements.
CAUTION
Before attempting to perform voltage and re-
sistance measurements, carefully follow in-
structions and observe notes on the voltage
and resistance diagrams. Carelessness may
cause additional troubles in the equipment
NOTE:
and make the troubleshooting job more diffi-
CONTROL
SETTING
cult. Never remove or connect a transistor
POWER
ON(UP)
with voltage applied to the circuit.
INTERNAL MODULATION
1000 ~
into the circuit; every effort should be made to trouble-
shoot the equipment without physically unsoldering and
DEVIATION METER
300KC
RANGE
removing the transistors. Paragraphs 3-10, 3-11, 3-12,
MODULATION
INT SINE
isolating trouble within the transistor stages.
600-1850
600
b. If all checks fail to indicate a defective part, check
FREQUENCY MC
the alignment of the signal generator.
c. Use the schematic diagram (fig. 5-8) to trace cir-
DEVIATION
FULLY CLOCKWISE
cuits and to isolate the faulty part.
EL6625-1633-45-TM -24
Figure 3-13 Normal waveform diagram.
3-10. Analysis of Measurements
tube back in the socket and take voltage and resistance
When measuring the resistance of circuit elements con-
measurements at the tube socket pins.
nected across the junctions of any transistor (base-
emitter or base-collector), consider the polarity of the
3-8. Isolating Trouble Within a Vacuum
ohmmeter and try measurements with the ohmmeter
Tube Stage
connected one way, and then reverse the leads. For ex-
When trouble has been localized to a tube stage, either
stage. If, when measuring resistor R1, the negative lead
through operational checks, short circuit tests, trouble-
of the ohmmeter is placed at the junction of resistors R1
shooting charts, stage gain measurements, or waveform
analysis, use the following techniques to isolate the de-
fective part:
a. Test the tube involved, either in a tube tester or by
substituting a similar type of tube which is known to be
good.
b. Take voltage and resistance measurements at the
tube sockets (fig. 5-5.).
c. Refer also to the dc resistances of transformers and
coils in paragraph 3-16.
d. If all checks fail to indicate a defective part, check
the alignment of the signal generator.
cuits and to isolate the faulty part.
NOTE:
3-9. Isolating Trouble Within a Transistor
UNLESS OTHERWISE INDICATED,
Stage
RESISTANCES ARE IN OHMS
CAPACITANCES ARE IN UP,
EL6625-1633- 45-TM- 26
When trouble has been localized to a transistor stage,
Figure 3-14. Typical common emitter stage.
late
.
3-16
