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Wireless Intercom Systems
Model C960
Technical Bulletin 9/27/99
New C921BA Base Station
Two problems have appeared only on new C921BA Base Stations. They have been corrected on higher serial
numbered units.
•
Low inbound menu microphone volume may be noticed on serial numbers below 0921001987, in
situations where the menu mic is more than four feet from the customer's car. The "Menu Mic Sens"
potentiometer must be turned up excessively for adequate inbound volume.
A field fix for this problem is to reduce the size of the two 1500-Ohm resistors in the attenuator
cable, shipped with the 3.5-Inch Duplex Microphone (78-6911-4476-6). A matched pair of resistors
of approximately 750 Ohms each will increase the inbound volume.
A permanent fix for this problem is to replace the 100 kilo-Ohm resistor with a 330 kilo-Ohm
resistor as shown in Figure 1 below: This is an 850 series surface-mount resistor, part number
P330KACT-ND. It may be ordered from Digi-Key at (800)344-4539
www.digi-key.com
or obtained
from 3M Technical Service.
If you are aware that this problem exists at a location, you can choose to fix it yourself by
performing one of the two fixes listed above, or return the Base Station to 3M for an exchange.
Please indicate why you are returning it.
C921BA Base Station
NE57
0D
C960
334
Change the 100k (104) resistor
here, to 330 k (334).
Figure 1
•
Cross talk may occur on serial numbers below 0921002348, when two Base Stations are in
the same area, such as, in a Dual Lane or Cross Lane System. When the Talk button is
pressed, the Talk LED will light on both Base Stations even though the second Base Station
is set for Lane 2.
Summary of Contents for C860
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