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Maintenance
The following procedures are designed to assist in the isolation
of malfunctions. The operations described should be undertaken
only after an investigation of all external connections and adjust-
ments has indicated, beyond reasonable d o u b t , that the problem
is actually w i t h i n the mixer.
Component Access—The 5306 contains t w o circuit board con-
figurations—a single assembly containing the circuitry f o r mixing,
line, o u t p u t and m o n i t o r amplification as well as the power
supply; and three dual-channel microphone preamplifier circuit
assemblies. Each microphone preamplifier assembly also contains
the input transformers and overload indicator circuitry.
To reach the mixer assembly f o r testing or service, the t o p cover
must be removed ( e i g h t # 6 sheet metal screws) exposing the
circuit board. To gain access t o the circuit's electronic com-
ponents, remove the heat sink f r o m the sub-chassis (three#6
machine screws) and the tone control switches f r o m the f r o n t
panel, push the circuit board straight back t o clear the switch
she
and lift it away f r o m the sub-chassis. The microphone pre-
amplifiers can be tested by removing the b o t t o m cover ( e i g h t # 6
sheet metal screws) over the three dual-channel circuit boards
which are mounted on the sub-chassis.
Note: The t w o mounting screws nearest the input transformers
of the microphone preamplifiers must be securely tightened
since these screws complete the main system ground for each
channel. Wherever a circuit board has been removed f r o m the
chassis, a visual check should be conducted for possible burned
components, loose connections or other obvious conditions which
might suggest a source of trouble.
Testing—All of the major circuits used in the 5306 are connected
in cascade; consequently, each successive unit must operate
properly in order t o test the following stages. A systematic
analysis should be performed in the following sequence:
A .
Microphone Preamplifier
B.
Mixing A m p l i f i e r
Line Amplifier
Z.
D.
Output Amplifier
E.
Monitor Output A m p l i f i e r
Note: Since all of the amplification stages of the 5306 employ
the principle of negative feedback, measuring A C signal levels
inside of the loop will not provide meaningful information. The
only significant data will be found in the signals present at the
input and o u t p u t of each major circuit.
Table I, DC Test Voltages, provides the DC voltages measured
w i t h respect t o ground f o r each transistor terminal. It should
be noted that a high input impedance (10 megohms or greater)
DC voltmeter should be used. Although ail o f the transistor
terminal voltages are important, the collector voltages, marked
w i t h an asterisk ( * ) , are the most significant when determining
that each major amplifier stage is operating properly.
DC Test Voltages
Transistor
Q 5 0 1 , 5 0 8
Q502, 509
Q 5 0 3 , 5 1 0
0 5 0 4 , 5 1 1
0 5 0 5 , 5 1 2
0 5 0 6 , 5 1 3
0 5 0 7 , 5 1 4
Q401
Q402
Q403
Q404
Q405
Q406
Q407
Q408
Q409
Q410
Q411
Q412
Q413
Q414
Q415
Q416
Q417
Q418
Q419
Q420
Q421
0 4 2 2
* O u t p u t mid-supply voltage for each stage.
8
Base
Emitter
Collector
23.3V
2 2 . 7 V
23.3V
22.7V
42.3V
42.8V
42.8V
43.3V
13.1V
13.1V
.1V
OV
,6V
OV
21.2V
20.6V
21.2V
20.6V
42.2V
42.8V
21.3V
20.6V
21.3V
20.6 V
41.4V
41.9V
1.2V
.6V
22.0V
22.0V
43.4V
43.9V
43.8V
44.2V
1.2V
.6V
22.3V
21.8V
22.3V
21.8V
43.1V
43.7V
43.8V
44.2V
1.2V
.6V
22.4V
21.8V
52.3V
52.7V
22.4V
21.8V
46.0V
45.1V
45.1V
44.5 V
42.3V
43.3V
OV
*23.2V
OV
13.1V
.1V
43.0V
42.2V
*21.5V
41.4V
42.2V
*21.2V
*21.2V
44.5V
43.4V
OV
*22.3V
*22.3V
44.5V
43.1V
OV
*22.5V
*22.5V
52.3V
46.0V
46.0V
52V
53V
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