Codan NGT 2010 RF Technical & Service Manual page 793

8571—Fault finding
Drawing
Table 9: Supply voltages for the Dual Line Equaliser PCB
Supply
B rail
+6 V bias
+5 V bias
+4 V bias
No signalling
No signalling can be due to a loss of one of the regulated supplies, a failure in the
microprocessor and control circuit, or a problem in the transmit/audio paths.
A study of the technical description of the signalling system should assist in checking for
a signalling fault.
If there is a second system available, then swap the units to assist in identifying the faulty
unit. However, if this is not possible, it is necessary to carry out a number of the tests to
locate the area in which the signalling has failed.
Checking the master 8571
To check the operation of the master 8571:
1
1
Checking other equipment
If the microprocessor and its associated circuits appear to be functioning, then check the
tone generator, the Bell 103 modem, and the signal path for possible failure.
354
08-03905
Description
+10 V regulated supply
+6 V reference
+5 V reference
+4 V reference
Initiate a channel change and use an oscilloscope connected across the line to
observe the control tone.
The 300 Hz control tone (nominally 700 mV p–p) combined with the FSK signal
should be seen for a short period after the channel change.
If there appears to be no activity when initiating a channel change, check all
regulated DC supplies for the master 8571 (see
If the signalling in the master 8571 appears to be working, then a fault could be due
to a failure in the line, in the slave 8571, or the transceiver.
Voltage
10 V ±0.2 V
6 V ±0.6 V
5 V ±0.5 V
4 V ±0.4 V
page 353, Voltage
NGT Transceiver System Technical Service Manual
Source
IC6
junction R2/R3
junction R3/R4
junction R4/R5
measurements).