Codan NGT 2010 RF Technical & Service Manual page 797

8571—Fault finding
Checking the 8571s
To check an 8571:
1
1
1
1
1
1
1
1
Checking the transceiver
If the interface cable is proved to be satisfactory, then the transceiver should be checked
(see
358
Check the DC input supply and the regulated supplies are correct for the 8571 (see
page 353, Voltage measurements).
Ensure that all units are connected to the line and equalised.
Remove the 8571 NGT I/F controller cable (Codan part number 08-05990) at the
8571 end.
Apply a 1 kHz tone at a level of 1.2 V p–p to the input of transformer T1 on the
Microprocessor & TCVR Interface PCB (connector P1 pins 14a and 16a of the Tcvr
Audio connector).
Using an oscilloscope, check if the 1 kHz signal is present at the output of the line
driver IC102 pin 5 on the Dual Line Equaliser PCB, and that it measures
approximately 800 mV p–p.
If the 1 kHz signal is present, then the 8571 is operating properly.
Check for possible faults in the transceiver and the interface cable.
If there is no audio at IC102, then the 1 kHz signal should be traced through the
receive path on the Microprocessor & TCVR Interface PCB.
Commence by checking the 1 kHz level at the secondary of the input transformer
T1. If correct, continue checking the receive path through IC2c switch C, then at the
output of the 300 Hz notch filter IC4, through IC2a switch A, then the output of
Audio Compressor IC7, and finally at the Rx audio bus (via the modem IC6).
Refer to circuit diagram
If the signal is absent at any of the test points, examining the neighbouring circuits
should assist in locating the fault.
page 69, NGT—Technical description
04-02690 for levels.
(2010)).
NGT Transceiver System Technical Service Manual