Fault Diagnosis - Racal Instruments RA-117 User Manual

11. Fault Diagnosis

INTRODUCTION
1. The following notes and test procedures enable the faulty section of the receiver to
be determined with the minimum of delay. Unless other- wise stated the meter on
the front panel is used for measuring purposes. This is set to R.F. LEVEL and the
reference figure is 100 A for all sensitivity tests.
2. Since the audio stages of the receiver are conventional and accessible, normal practice
will serve to trace any fault which may occur in this section.
TEST EQUIPMENT REQUIREMENTS
3. The following test equipment will be required:
(1) Valve Voltmeter.
(2) 12pF trimmer capacitor.
(3) Signal generator.
NOTE:The input capacitance of the valve voltmeter must be padded to 12pF by the
trimmer or alternatively by a fixed capacitor. Before the value or the trimmer or
the fixed capacitor can be selected, the input capacitance of the valve voltmeter
must be know. If the trimmer is used this should be connected across a capacitance
bridge and set to the required value.
FAULT DIAGNOSIS
4. Set the controls on the front panel as follows:-
5. Remove the valve V12 and crystals XL1 and XL300, and connect the output of the
signal generator to socket SKT303.
6. Set the BANDWIDTH control to 100 c/s and tune the signal generator for maximum
indication on the meter at 100 kc/s. Switch through the bandwidth positions. The
sensitivity should be approximately as follows:-
3 kc s
100 c s
300 c s
1 2 kc s
6 5 kc s
13 0 kc s
7. In the event of the figure above not being realized, the renewal of one or more of the
following valves will probably effect an improvement.
A.F. GAIN set to max.
R.F./I.F. GAIN set to max.
B.F.O. switch to off.
LIMITER switch to OFF.
SYSTEM switch to MAN.
less than 800 V for a deflection of 100 A
To be within 10dB of sensitivity measured on 3kc s position
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