Service manual

Notes to Circuit Diagram
D.C. Voltage Measurements:
Check the DC voltages first, because any deviation from
the nominal voltages will affect the AC voltage. In the power
amplifier, Q31 to Q38, the key DC voltages are
94 (col-
lector of Q33, 035, and Q37), -22 (collector of Q31),
and the split voltage at the junction of R17, R19, R20, and
R22. If these three key DC voltages are correct, then pro-
ceed with the AC voltage measurements.
The numbers within the symbols
o on the circuit dia-
gram denote the D.C. voltage at that point with the follow-
ing test conditions:
1. Voltages measured at points indicated with respect to
chassis, unless otherwise indicated.
2. Line voltage
- VA302-C: 120v. 60 Hz.
VA302E-C: 120/240~. 50/60 HZ.
VA302E6-C: 100, 120, 140, 200, 220, or
240v. 50/60 Hz.
3. No input signal applied.
4. D.C. voltage measurements may vary
&20% from the
values shown.
5. Measured with a VTVM of
11-megohms input impe-
dance.
6. Q27 transistor voltages on the circuit diagram are with
the master reverb switch in the "IN" position. With the
master reverb switch in the "OUT" position, Q27 volt-
ages are: emitter 4.0, base 0.0, and collector 22.0.
A.C. Voltage Measurements:
The numbers within the symbols
on the circuit dia-
gram denote the A.C. voltage at that point with the follow-
ing test conditions:
1. Voltages measured at points indicated with respect to
chassis, unless otherwise specified.
2. Line voltage
- as specified above.
3. 1,000
Hz. signal applied to input, in "IN" position, at
0.8 millivolts.
4. Measured with an A.C. VTVM of 1.0 megohms or
greater input impedance.
5. Noninductive load of 8 ohms, 200 watts connected to
speaker output jack for Q31 through Q38.
6. Echo input and output jacks to be open; echo gain
control set to maximum.
7. All anti feedback switches set to "OUT" position.
8. Reverb intensity set to minimum.
9. All tone controls set to 12 o'clock position.
10. All volume controls set to maximum.
11. Master reverb switch set to
"OUT" position except as
noted.
12. Individual channel reverb switches set to
"OUT" posi-
tion except where noted.
13. Transistor voltage measurements for Q20 through Q27
must be made with master reverb switch and individual
channel reverb switches in the "IN" position.
14. A.C. voltage measurements may vary ?:50°h from the
values shown.
15. For A.C. measurements on Q25, Q26, and Q27, the
frequency may be varied
t100 Hz. to obtain the A.C.
measurements shown.
16. For VU Meter specifications, see page
9.
Ohmmeter Measurements:
With the A.C. line cord unplugged and the power switch
in the "OFF" position, the following ohmmeter measure-
ments may be made:
1. Reverberation Assembly M2 input and output coils
approximately 180 ohms.
2. Anti feedback Inductors M3 approximately 300 ohms.
3. B- to ground approximately 50 ohms
4. Ohmmeter plus probe to the junction of R17,
R19, R20,
and R22, ohmmeter minus probe to ground: greater
than 100 ohms.
5. Ohmmeter plus probe to BI, ohmmeter minus probe
to the junction of R17,
R19, R20, and R22: greater than
100 ohms.
6. To test transistors and diodes, see page 16.
Shure part numbers are not shown in the parts list ac-
companying the circuit diagram if parts are readily avail-
able through local electronic parts supply distributors. In
these instances, the circuit diagram will show the value of
the standard parts.
All capacitor values are shown in microfarads. All
non-
electrolytic capacitors are to be 100 volts or more unless
otherwise specified in the circuit diagram. Electrolytic ca-
pacitors are shown in microfarads and volts.
All resistor values are shown in ohms. Resistors are all
to be 10% tolerance unless specifically noted on the cir-
cuit diagram.
Resistors shown in the upper two lines of circuitry on the
diagram are
'/4 watt unless otherwise specified. Resistors
shown in the lower line of circuitry are
l/2 watt unless other-
wise specified.
The following ground symbols denote:
Chassis
Ground
Preamplifier
1
Ground
-
-
Reverb
Driver Ground