Modem And Telephone Line Check - Black Box 325 User Manual

B.5 Modem and Telephone Line Check
Step 1: Configure the modem for LOCAL ANALOG LOOP WITH TEST PATTERN. This terminates
the local modem telephone lines into 600 ohms and connects the local modem transmit output amplifier
back to its own receiver through the AGC. Transmit input data from the terminal is inhibited and is
substituted with a V.52 test pattern.
This test checks operation of the local modem's modulator and demodulator circuitry and should be
attempted at both local and remote sites if operators are available.
• When random errors are present, the TEST PATTERN ERRORS display counts receive errors.
• If the circuitry is working properly, the front-panel indicators show the following:
Configure the modem for LOCAL ANALOG LOOP to switch the transmitter back to its normal data
input.
• If the transmit data input is in a mark hold condition, both the TD and RD indicators should remain
off.
• If the transmit data input is in a space hold condition, both the TD and RD indicators should come
on. All other indicators should remain the same except for CS, which should turn on.
• If the indicators are correct, the modem is probably operating correctly.
• If the preceding tests were not successful, call for technical support.
QM CS RS
On Off
Figure B-1. Front-Panel Indicators.
APPENDIX B: Fault Isolation Procedure
CD RD TD
On or Off
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