Shure SCM268E, User Manual, Page: 7 / 28

7
Internal Modifications
Internal Modifications
Voltages in this equipment are hazardous to life. No user-serviceable parts
inside. Refer all servicing and modifications to qualified service personnel.
Disassembly
To access the printed circuit board (pc board) for internal modifications,
use the following steps:
1. Unplug the power cord.
2. Remove the knobs and retainer nuts from
the front panel (See figure 2).
Knob Assembly
FIGURE 2
3. Remove the four screws at each corner of the back panel.
4. Remove the two screws at each bottom corner of the front panel.
5. Slide the back panel and pc board out from the rear of the chassis.
When reassembling the SCM268, DO NOT OVERTIGHTEN the knob retainer nuts.
Use a minimal amount of force to secure the nut (0.6-0.8 N m (5-7 in lb)). Damage to
the internal components will result if too much force is used.
Low-Cut Filter
To bypass the built-in low-cut filter for a given channel, remove the speci-
fied resistor and place a 10µF to 33µF capacitor in the specified pc board
location (polarity does not matter). Refer to the following table:
Channel
Remove Resistor
from:
Place 0µF to 33µF
Capacitor in:
1 R18 X17
2 R28 X27
3 R38 X37
4 R48 X47
To select a particular corner frequency for the low cut filter, remove the
R18, R28, R38, or R48 resistor for a given channel as specified above.
Then, in the corresponding pc board location (X17, X27, X37, or X47),
place a capacitor of the specified value (polarity does not matter). Refer
to the following formula for selecting the correct capacitor value for the
desired corner frequency.
C = 26.5/F
where:
C = value of capacitor in µF
F = corner frequency (-3 bB) for low-cut filter in Hz
The following table lists the low-cut frequency corners for some of the
most common capacitor values:
Capacitor Value (µF) Low-Cut Frequency Corner (Hz)
.033 803
.047 564
.068 390
.1 265
.22 120
.33 80
.47 56
.68 39
1.0 26.5
2.2 12
Phantom Power Disable
To disable phantom power for a given microphone input, remove the spec-
ified resistor as listed in the following table:
Channel Remove Resistor:
1 R15
2 R25
3 R35
4 R45
Line Pad
To insert a 50 dB line pad for a given microphone input, remove the speci-
fied resistor and short the solder points at the specified pc board locations.
Refer to the following table:
Channel Remove Resistors: Short Solder Points:
1 R12, R13, R15 X11 and X14
2 R22, R23, R25 X21 and X24
3 R32, R33, R35 X31 and X34
4 R42, R43, R45 X41 and X44