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General Servicing and Aligment Procedures
33
13. General Servicing and Aligment Procedures
13.1. General Servicing
INTRODUCTION
1. The following tests will assist in checking the performance of the receiver.
2. Component layout illustrations, fig.8 to fig.23 inclusive, give an overall picture of the
receiver sub-assemblies and chassis underside.
3. Removal of the main base cover will, without removal of further covers, reveal the
power and audio stages, and the 100 kc/s I.F. amplifier chassis.
4. To gain acces to other stages, furher covers must be removed, they are the second
mixer (compartment 7) and the crystal oscillator/amplifier and harmonic generator
stages (compartments 4, 5 and 6) fig. 15.
TEST EQUIPMENT REQUIREMENTS
5. The following test equipment will be required to carry out tests on the receiver:-
(1) Telephone headset
(2) Output power meter
(3) Signal generator
(4) Multimeter
13.2. Receiver Tests
RECEIVER OVERALL GAIN TESTS (C.W.)
6. Perform a sensitivity test as follows:-
(1) Set the controls on the receiver as follows:-
R.F.RANGE
2 – 4 Mc/s
MEGACYCLES
3
KILOCYCLES
500
R.F ATTENUATOR
MIN.
SYSTEM switch
MAN.
BANDWIDTH
3 kc/s
B.F.O. switch
ON
B.F.O. NOTE
1 kc/s
R.F./I.F. GAIN
fully-clockwise
(2) Set the controls of the output meter for 600 ohms impedance and a range of
6mW. Connect the output meter across one of the 600 ohm 3mW windings and
terminate the other windings with resistor to match their marked impedance.
(3) Set the controls of the signal generators for a c.w output of 1
µ
V at 3
.
5 Mc/s
and an impedance of 75 ohms. Connect the output of the signal generator to the
antenna input of the receiver.
(4) Tune the receiver to the output frequency of the signal generator and check that
a reading of 3mW can be obtained within the range of the A.F. GAIN control.
(5) Repeat the test with the B.F.O. switched off and a 30% modulated signal at level
of 3.5
µ
V from the signal generator.
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