Shure SE30 - Manual (Page 26)

SERVICE INSTRUCTIONS (Cont’d)
3.
4.
5.
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push-on retainers so that it may be raised above the
chassis for service without complete removal. With all
power turned off, depress retainer locking tab, if any,
and pry each corner of the board from its retainers. Lift
the board straight up assuring that all wires clear any
obstructions, and position the two lower board mount-
ing holes over the two upper plastic retainers. Snap the
board over the retainers, thus exposing the component
side and most of the conductor side of the board.
After positioning one or more boards in this manner,
the SE30 may be operated and measurements made.
All connections to printed circuit boards are made by
push-on terminals crimped to color-coded wires. To
remove a printed circuit board, first turn off all power
and remove ac line cord, then grasp each brass ter-
minal with long-nose pliers and pull away from board.
The board may then be pried from its retainers and
lifted out of the chassis.
Figure 6 illustrates the location and position of each
printed circuit board component. Note that all such
components have three-digit reference numbers, the
first digit of which denotes the printed circuit board
number. The colors of wires connected to each ter-
minal are also shown to aid in reconnecting boards.
Color abbreviations with asterisks refer to stranded
No. 20 AWG wiring, and those in parenthesis refer to
integral component leads. All other wires are smaller,
stranded No. 24 AWG.
Printed Circuit Board 4 requires special handling, as
noted in Figure 6B. To avoid possible erratic operation
under high humidity conditions, the area of the board
which includes Q401, R401-404, and C401-403 must
be kept free of contamination from perspiration, skin
oils, and the like on both sides. This area should not
be touched with the fingers, and if any of these com-
ponents must be replaced, soldering flux must be re-
moved by brushing with a solvent such as clean wood
alcohol (methanol) or denatured alcohol. (Do not use
rubbing alcohol.) After flux removal, rinse with dis-
tilled water to remove electrolyte contaminants.
CAUTION: Alcohol is flammable. Do not use near fire.
Note that FET Q401 is mounted inverted to the board
with a direct soldered connection between R402 and
the gate lead.
Integrated circuits MC201 and MC301 are mounted in
14-pin sockets to facilitate removal and replacement.
The notch on one end and a dot or mark identify pin 1,
which must be positioned as shown in Figures 6A and
6B and as indicated on the printed circuit board.
Typical voltage measurements are given for Various
points in the circuitry in Tables 2A, 2B, and 2C. The
notes to Schematic Diagram and Test Voltages Outline
the test conditions for these measurements. Voltages at
all printed circuit board terminals are given in Table
2A, and board-mounted transistor and integrated cir-
cuit terminals voltages are given in Tables 2B and 2C.
All voltages are measured with respect to chassis
ground.
Replacement of Printed Circuit Boards 2, 4, or 5, or
of MC201 will necessitate recalibration of the com-
pression system as outlined below. In addition, Printed
Circuit Board 3 replacement requires Gated Memory
recalibration, and Printed Circuit Board 5, or meter
Ml replacement require VU Meter calibration. Com-
pression system calibration should also be checked
if meter M1 is replaced.
CALIBRATION
Each SE30 Gated Compressor/Mixer is individually cali-
brated at the factory with six internal trimming potentiom-
eters and a selected fixed resistor, to compensate for
individual component variations and to assure uniform and
accurate performance. The complete calibration procedure
is given here for qualified service personnel with access
to laboratory quality instruments, in the event that com-
ponent replacement or changes in internal control settings
necessitate recalibration.
For those without adequate facilities, the complete unit
may be returned to the factory for calibration. Carefully
repack the unit and return it to the factory Service Depart-
ment. The unit will be returned to you prepaid.
EQUIPMENT NEEDED:
A high-impedance (2 megohm or greater), high-sensi-
tivity (10 mV full scale or better) ac voltmeter, such as a
Hewlett-Packard 400 GL or Ballantine 861, is necessary for
accurate results. The meter should be equipped with a
clip-on shielded test cable.
In addition, a sine-wave audio generator, capable of
producing 1 volt at 1 kHz with less than 1% total harmonic
distortion, is desirable. A generator with an accurate 10
dB stepped output attenuator, such as the Hewlett-Packard
204D, will greatly simplify changes in input level necessary
during the procedure. A shielded cable to connect the out-
put of the generator to the professional three-pin female
Input 1 receptacle will be needed. Unbalance the generator
output (low side connected to chassis), if generator output
is balanced, and wire the cable so that input connector
pins 1 and 3 are to the low side of the generator and pin 2
is to the high side.
There are three different portions of circuitry which re-
quire calibration: the Gated Memory, the compression sys-
tem, and the VU meter. A standard blade screwdriver may
be used to adjust the trimmer potentiometers during the
Gated Memory and compression system calibration. VU
meter calibration requires the selection of a fixed resistor
and soldering it in place on P.C. Board 5.
During the Gated Memory and compression system Cali-
bration, the internal signal level at terminal A of P.C. Board
3 is monitored and adjusted. The signal voltage at this
point will be referred to as E3A. The test signal is provided
by an external sine-wave generator, or the internal Tone
Oscillator may be used. If an external generator is used,
connect its mating cable to the Input 1 connector (13A) with
the Input switch (14A) set to LINE, and the Input 1 Filter
switch (2A) set to IN. Adjust the generator for 1 volt output
at 1 kHz. If the Tone Oscillator is used, set the front-panel
Input 1 Filter switch (2A) to TONE OSC.
If the Tone Oscillator or an external generator without a
stepped attenuator is used, the voltage at terminal A of
P.C. Board 3 (E3A) should be adjusted to the required
values by the Input 1 control (1A). If the external generator
does have a stepped attenuator, the Input 1 control (1A)
should be adjusted so that a l-volt generator output results
in 1 volt at terminal A of P.C. Board 3. Lower levels are then
obtained by using the generator’s attenuator.
Calibration must be performed with the top cover re-
moved to permit access to the trimmer potentiometers and
test points, and during compression system calibration,
removal of the bottom cover is also suggested. For com-
plete safety from hazardous powerline voltages, the SE30
should be battery-operated during calibration, using fresh
batteries which indicate +1½ VU or better on the meter,
with the Batt. Check switch (9) actuated and the Power
switch (11) ON.