Shure VA 300 - Manual (Page 16)

OHMMETER CONNECTIONS O H M M E T E R R E A D I N G
“Plus” Lead “Minus” Lead
Collector
Emitter
Collector
Emitter
Base
Base
Emitter
Collector
Base
Base
Collector
Emitter
N.P.N. Transistor P.N.P. Transistor
High
High
High
High
L o w
L o w High
High
L o w
L o w
High
High
With the ohmmeter “plus” probe on the anode end of a
d i o d e , a n d t h e “ m i n u s ” p r o b e o n t h e c a t h o d e e n d , t h e
ohmmeter should read approximately 2000 ohms or less. With
the meter probes reversed, a reading of about 10,000 ohms or
more should occur. If either of these conditions is not met, the
diode should be replaced.
Power Drain Resistor (R
SEL
):
The following condition may occur after replacement of
d r i v e r t r a n s i s t o r s Q 3 3 a n d Q 3 4 , o u t p u t t r a n s i s t o r s Q 3 5
through Q38, or diodes D6 and D7. If the unit appears to
o p e r a t e a t a n e x c e s s i v e l y h i g h t e m p e r a t u r e o r t h e r m a l l y
recycles after about 10 minutes with no signal input, the
“cold” standby power drain may be excessive (up to 20 watts
higher than normal; a higher power drain indicates further
circuitry problems). The nominal power drain under these
conditions should be 60 watts; if the measured figure exceeds
75 watts, insert a resistor (R
S E L
) in parallel with the 56-ohm
resistor between the base of transistor Q33 and the junction of
diodes D6 and D8 (figure 17, page 21). R
S E L
( ½ W , 1 0 % )
should be either 180 ohms to decrease the power consumption
by 20 watts, or 82 ohms to decrease the power consumption
by 30 watts.
Lamp Replacement:
The two lamps I2 and I3, Figure 12, Page 14 which provide
illumination of the front panel controls are 115 to 125 volt,
15 watt incandescent bulbs. These bulbs are soldered and
epoxied into the molded plastic sockets in order to meet
Underwriters’ Laboratories requirements. The assembly may
be removed by unsoldering the lamp leads at the terminal
strips and removing the screw that holds the socket to the
chassis.
Reverberation Assembly:
The Reverberation Assembly M3, Figure 13, Page 15 may
be removed and returned to the factory Service Department
for repair if a malfunction should occur. The amplifier can be
operated without this assembly. To eliminate possible damage,
or shock hazard, the plug-in cables should be temporarily
inserted in the nylon inserts normally used to mount this
sub-assembly. If extensive damage has occurred, a replacement
Reverberation Assembly may be ordered through the dealer or
from the factory Service Department.
Replacement Parts:
Parts that are readily available through local electronic parts
distributors are not shown on the accompanying Parts List.
Their values are shown on the circuit diagram. The special
custom made parts are shown on the Parts List.
The commercial alternates shown on the Parts List are not
necessarily equivalents, but may be used in the even that direct
f a c t o r y r e p l a c e m e n t s a r e n o t i m m e d i a t e l y a v a i l a b l e . T o
maintain the highest possible performance and reliability,
S h u r e f a c t o r y r e p l a c e m e n t p a r t s s h o u l d b e u s e d . W h e n
ordering replacement parts, specify the Shure Replacement Kit
N u m b e r , d e s c r i p t i o n , p r o d u c t m o d e l n u m b e r a n d s e r i a l
number.
EQUIPMENT DESIGNED FOR USE
WITH THE VA300 VOCAL MASTER
VA300-S
VA301-S
PM300
A3PC
A3PC-C
A3PC-S
A31PC-S
A3S-C
ASS-S
A 5 0 X C
A3S-T
A95 Series
Vocal Master Speaker Column
Vocal Master Monitor Speaker
Power Master Booster Amplifier
Soft Cover Set
Console Soft Cover
Speaker Column Soft Cover
Monitor Speaker Soft Cover
Fold-Up Console Stand
Speaker Stand
15m (50 ft) Speaker Extension Cable
Speaker Stand
Low Impedance Transformers
GUARANTEE: This Shure product is guaranteed in normal use to
be free from electrical and mechanical defects for a period of one
year from the date of purchase. Please retain proof of purchase
date. This guarantee includes all parts and labor.
SHIPPING INSTRUCTIONS: Carefully repack the unit and return it
prepaid to the factory. If outside the United States, return the unit
to your authorized Shure Service Center for repair. The unit will be
returned to you prepaid.
SERVICE: If information or service should be required, contact
your local Shure Vocal Master dealer explaining your difficulty in
detail. In addition, the Shure factory service department will be
ready to assist you immediately upon request.
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