E.F. Johnson and Other Unpowered-Microphone-Input RadiosPARTVALUETYPE
Certain radios such as those manufactured by E.F. Johnson do notQ30486A350NPN Transistor
have biased audio, that is, there is no power on the audio line (see
C31610 mF 35 wvdcElectrolytic Capacitor
Figure 6). For radios with this type of input, the audio output must
R317100K1/4 W 2% Resistor
be wired to pin 6 (not pin 2) of the 885TT'modular connectors . This
is accomplished by using the red lead (normally the powered audioR3181K1/4 W 2% Resistor
lead) for power only and the white lead for audio, and moving jump-2. Disconnect the blue wire from location W308 and connect it to
er D-E (see procedure below). This places a bias resistor and noiseW310. See Figure 8.
filter in the mic circuit.
Blue wire to hang-up button
IMPORTANT: To avoid permanent damage to the 885TT, this modifi-
cationmus t be performed before using the 885TT with any equip-
ment listed in the MODULINK Cordset Table as requiring it.
W310
TO PIN 2
12-18 VDC
NON-DC-BIASED INPUT CIRCUITS
FIGURE 6C316 R317
R318 Q304
1. Open the microphone as described in the oModificationso para-
graph above.885TT REAR CIRCUIT BOARD
LOCATIONS FOR LOGIC-INVERTING MODIFICATIONS
2. Locate red jumper wire (W301) connected between points aDo
FIGURE 8
and aEo as shown in Figure 7.
REPLACEMENT PARTS
3. Using diagonal cutting pliers, clip and remove this wire from
Keypad . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . RK269
both points.
Membrane Switch Assembly. . . . . . . . . . . . . . . . . . . . . RK270
4. Solder ajumper wire (W309) between locations aFo and aGo as
Leaf Switch Assembly. . . . . . . . . . . . . . . . . . . . . . . . . . RK271S
shown in Figure 7.
Cable and Modular Plug. . . . . . . . . . . . . . . See Cordset Table
5. Reassemble the microphone.FURNISHED ACCESSORY
NOTE: This type of radio normally handles a low-level mic signal;
Screwdriver. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80B498
use of the 885TT will probably require that the audio and
OPTIONAL ACCESSORY
DTMF gain controls be turned down.
Mounting Bracket (3 in kit). . . . . . . . . . . . . . . . . . . . . . RK6MB
Red jumper W301
INFORMATION TO USERS
This equipment has been tested and found to comply with the limits for a Class B
Ddigital device, pursuant to Part 15 of the FCC Rules, and as set out in the Radio
Interference Regulations of the Canadian Department of Communications. These
limits are designed to provide reasonable protection against harmful interference in
a residential installation. This equipment generates, uses and can radiate radio
FG
frequency energy and, if not installed and used in accordance with the instructions,
Emay cause harmful interference to radio communications. However, there is no
guarantee that interference will not occur in a particular installation. If this equip-
ment does cause harmful interference to radio or television reception, which can be
determined by turning the equipment off and on, the user is encouraged to try to
correct the interference by one or more of the following measures:
Attach jumperwReorient or relocate the receiving antenna.
W309 here
wIncrease the separation between the microphone and receiver.
885TT REAR CIRCUIT BOARDwConnect the microphone transmitter to an outlet on a circuit dif-
JUMPER LOCATIONSferent from that to which the receiver is connected.
FIGURE 7wConsult the dealer or an experienced radio/TV technician for
help.
Radios with Inverted Logic
Certain radios such as those manufactured by Ericsson have a
positive-going circuit when the mic is on-hook. The logic of the
885TT can be inverted for compatibility with these radios as fol-
lows:
1. Add the following components to the rear circuit board in theSHURE Incorporated Web Address: http://www.shure.com
positions shown in Figure 8.222 Hartrey Avenue, Evanston, IL 60202?3696, U.S.A.
Phone: 847-866?2200 Fax: 847-866-2279
In Europe, Phone: 49-7131-72140 Fax: 49-7131-721414
In Asia, Phone: 852-2893-4290 Fax: 852-2893-4055
Elsewhere, Phone: 847-866?2200 Fax: 847-866-2585
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