8571—Fault finding
NGT Transceiver System Technical Service Manual 359
No transmission, with signalling
If transmission is the only fault in the remote control system then the areas to be checked
are the transmit audio path in the master 8571, the transmit audio path in the slave 8571,
and the transceiver as follows.
Checking the master 8571
To check the master 8571:
1 Talk into the microphone and check if the speech can be measured on the phone line
with an oscilloscope.
If speech is present on the line, the problem is unlikely to be in the master 8571. In
this case, continue at the next section, Checking the slave 8571.
If no speech is present, continue with this section.
1 Check all regulated supplies for the master 8571 (see page 353, Voltage
measurements).
1 Apply 1 kHz audio at a level of 50 mV p–p to the local microphone input and
operate the local PTT.
1 If the signal is absent at any of the test points, examining the neighbouring circuits
should assist in locating the fault.
Checking the slave 8571
To check the slave 8571:
1 Hold down PTT on the handset, then apply a 300 mV p–p 1 kHz audio to the local
Tx audio input.
1 With an oscilloscope, check the line input to the 8571 for a signal mixed with the
1 kHz transmit audio.
NOTE
The following fault finding procedure is based on a remote control system
consisting of a single master 8571, a single slave 8571, and a transceiver.
In the case of multiple systems, consideration must be given to the other
units within the network when tracing this type of fault.
NOTE
If it is not possible to operate the PTT in the master 8571, a signalling
fault may also exist. This should be repaired before continuing to
investigate the fault causing no transmission (see page 354, No
signalling).
Drawings 08-03905 and 08-03993
NOTE
These signals may only measure a few millivolts and depend on the
attenuation of the line.
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