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Set the Distortion Analyzer FUNCTION to DISTORTION and adjust the
Distortion Analyzer Dial and Balance controls for minimum
indication .
Set the Distortion Analyzer MODE to AUTOMATIC and adjust R30 ( DIST )
for a meter indication of greater than 60 dB down from
Odd reference .
1-26 .
TROUBLESHOOTING PROCEDURE .
5-27 .
The following paragraphs are provided as an aid to troubleshooting the Model
204C .
These operations should be undertaken only after it has been determined that
the difficulty cannot be eliminated by the Adjustment and Calibration Procedures ,
Paragraph 5-17 .
An investigation should also be
made to ensure that the trouble
is not a result of conditions external to the Model 204C .
5-28 .
Before troubleshooting the Model 204C ,
read Section IV ,
Principles of Oper
ation ,
for familiarization with circuit operation .
5-29 .
Conduct a visual check of the Model 204C for possible burned or loose com
ponents ,
loose connections ,
or any other condition which might suggest a source of
trouble .
5-30 .
Voltages have been provided on the schematic diagram as an aid to trouble
shooting .
In some cases the voltages are shown to the nearest tenth of a volt . This
does not mean that the voltages should be the exact value shown , but rather they are
meant to indicate the base to emitter voltage drop of the transistors .
-31 .
The inner cabinet provides the chassis ground path for C1 .
When the cabi
et
is
removed for troubleshooting ,
connect a short jumper lead from
the bottom
of MP26 ( see Figure 6-1 ) to the metal tab protruding just below it .
This will allow
the oscillator to operate with the inner cabinet removed .
5-32 .
Some potential
malfunction symptoms and the associated probable causes
are listed in Table 5-5 .
Table 5-6 .
Troubleshooting Guide
SYMPTOM
PROBABLE TROUBLE
Check Power Supply and BIAS level .
Check BIAS control at A1Q1 gate . If ineffective ,
check Aisi and BIAS path .
If good ,
check
A1Q3 ,
A1Q7 ,
A1Q8 .
Check in NORM Mode at 100 Hz on X100
RANGE . If oscillations are present , replace
A1C9 with a higher value .
(Perform
High
Frequency Adjustment
Paragraph 5-24 . )
Change A1C9 to lower value .
(Check for high
frequency oscillations after change ).
Check A1CR4 ,
A1CR5 ,
A1R41 ,
and A1R42 .
( High Freq .
Cal )
Crossover Distortion
Microphonics or discontinuities
Check C1 wiper contacts on both rotor sections.
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