TM 11-6625-847-45
obtained on the AN/URM-145 with those listed in the
dividing the output voyage of the transistor stage under
output column. Agreement within 10 percent indicates
test by the input voltage to the transistor stages
within normal operations. Stage gains computed by
b. Stage Gain Chart.
TEST connection
VOLTAGE
AMPLIFIER
AN/GRM-50-
AN/URM-145
(Mv)
module
Input to
Output of
Stage
transistor
transistor
gain
stage
stage
AR3
Connector J1
Collector of Q1
50
780 10%
15.6 10%
Connector J1
Connector J3
780
590 10%
0.76 10%
(Q2)
AR1, AR2,
Connector J
Collector of
50
847 10%
16.9 10%
AR4,and
Q1
AR5
Connector J1
Connector J3
847
625 10%
0.74 10%
(Q2)
When measuring the resistance of circuit elements
2-17. Isolating Trouble Within Stage
connected across the junctions of any transistor (base-
emitter or base-collector), consider the polarity of the ME-
When trouble has been localized to a stage, use the
26(*)/U and try measurements with the ME-26(*)/U
following techniques to isolate the defective part:
connected one way; then reverse the leads. For example,
a. In-Circuit Transistor Voltage Measurements. If
used in each of the amplifier modules (AR1 through AR5).
transistors are wired in the circuit, troubleshoot the
If the positive lead of the ME-26(*)/U is placed at the
equipment without physically unsoldering and removing
junction of R2 and R3 and the negative lead is placed at
transistors. If transistors can be removed without the use
ground when measuring RS in this circuit, the ME-26(*)/U
of a soldering iron, test them out of the circuit. If a
battery forward biases the base-emitter junction, causing
transistor tester is available, test the pluckout transistors
a short circuit between the base and emitter. This places
before making other circuit test For in-circuit to , make
RS in parallel with R4 and R5. The MS 26(*)/U indication
the transistor dc voltage measurements indicated on the
will be slightly less than 60 ohms because of the parallel
schematic diagram of the module being tested. Carefully
resistances. If the ME-26(*)/U leads are then reversed,
follow instruction and observe notes on schematic
the transistor will be reverse-biased, causing a very high
diagrams; carelessness may cause more troubles in the
resistance to appear between the base and the emitter. In
equipment and make the troubleshooting job more
this case, the indication would be 820 ohms, the value of
difficult. Do not remove or insert a transistor with voltage
R3. If the indication is the same in both case, the
applied to the circuit. If the dc voltage at the emitter,
transistor is probably open-circuited or short-circuited.
collector, or base of the transistor being checked is
Consider, all, that differ values of resistance will be
abnormally low or high, make in-circuit transistor
obtained with the ME-26(*)/U on different ranges. For
resistance measurements using the techniques described
example, if the transistor junction or a resistor plus the
in b below.
transistor junction is measured in the forward direction or
the RX10 range, the actual indication will be less than if
b. In-Circuit Transistor Resistance Measurement.
taken with the ME-26(*)/U ok the RX100 range.
2-6
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