ZETRON 748, Technical Manual

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Installation
025-9368H 23
IN CASE OF DIFFICULTY
In case of installation difficulty, call Zetron for a Model 748 Applications Support Engineer. Please
have the serial number of the unit and/or the Zetron order number when you call. If the call is made
from the installation site by the installer or radio technician, the problem can usually be solved over
the phone.
Zetron, Inc.
28 Campbell Court, Campbell Road,
Bramley, TADLEY, Basingstoke,
Hants, U.K.
RG26-5EG
Tel No: +44 (0) 1256 880663
FAX No: +44 (0) 1256 880491
MISCELLANEOUS SERVICE NOTES
1. When the unit is reset or powered on, an automatic memory test will be executed. If greater than
20 memory errors are detected in the user programming, the unit will reset all of the user
database to the default settings. Any user with bad checksum will be marked as such and can be
displayed under System Statistics in the Diagnostic menu.
2. If the audio does not sound correct, perform an audio sweep test by generating an audio signal on
the RF input of the repeater (of known deviation), and monitor the repeater output deviation. The
deviation should be fairly flat from 300 to 2500 Hz.
3. When using the internal noise detector for COR, if the COR polarity switch seems backward, the
audio input from the receiver may not have enough high frequency content (greater than 6Khz)
for the noise detector to operate. It is usually caused by low pass filtering of the discriminator
signal. An alternate connection point must be found in the receiver which provides unfiltered
audio, or a receiver generated COR signal must be connected.
4. The Carrier LED MUST follow carrier activity on the channel. It must be lit with carrier present,
and extinguished when carrier is absent. If it is always off, the Model 748 will not function
correctly.
5. The Carrier and DTMF LED's are hardware controlled. The drive for these LED's are also the
inputs to the microprocessor. When trying to troubleshoot an installation, you can use these as
indicators of what the software is seeing.
6. If the unit is non-operational and the AUX LED on the front of the unit slowly pulses, contact
Zetron Applications for further assistance.
7. The hybrid balance adjustment is even more important with the Voice Prompts option installed.
If the hybrid is misadjusted, you may not be able to overdial DTMF through the Welcome
prompt.