User's Manual

MX800 Transceiver Fault Finding
Adjust the ‘Transmit Power’ control towards maximum looking for an
increase in the RF power output level. If there is no substantial changes go to
the diagnostics screen and check that the Forward power and the Reflected
power levels are not abnormal. NOTE, if there is a high reflected power
indication the MX800 firmware would hold the PA power low.
If the Diagnostics shows abnormal, then check the voltage on pin 62 of IC1
on the Mother Board. If the voltage is low i.e. <200mV then the likely fault
is IC1. If the voltage is >200mV then the likely fault is within the PA
module.
If the Diagnostics shows normal, then check the RF level from the Exciter
module by connecting a Power Meter directly to the Exciter RF connector.
Adjust the ‘Transmit Power’ control in MXTOOLS to maximum, the RF
level should be >+23dBm (200mW). If not go to section 6.4, if so the PA is
probably faulty and go to section 6.5
If there is NO RF power output, check that the ‘Transmit Power’ control in
MXTOOLS has not been set to zero (0) or is at a very low level. If so, apply a
PTT and increase the power control until the desired power is achieved. If
not, apply a PTT then check that pin 21 of IC1 is LOW, collector of TR3 is
LOW and pin 13 of IC7 is HIGH. If these are OK, then the Exciter or PA
may be faulty. Go to section 6.4, or section 6.5.
Inject a 1 tone @ –10dBm via pin 9 of the 15-way connector at the rear of
the radio and check for 1.5 kHz (NB)/ 3 kHz (WB) peak to peak demodulated
deviation.
If the audio deviation is incorrect then go to the Transmitter alignment
procedure in section 5.
If there is no audio modulation then check the audio level on pin 13, IC11on
the Microcontroller PCB.
If there is no audio on the above test point then go to section 6.2 else go to
section 6.4
6.1.2 Receiver Section
Using MXTOOLS Diagnostic’s check the RXVCO locking voltage is
between 2 – 18 V and there is no RXVCO ‘Unlock’ alarm displayed.
If the Rx locking voltage is out of spec then go to section 6.3.
Inject a –60 dBm RF test signal on the receiver frequency modulated with a
1kHz tone @ 1.5 kHz (NB) / 3 kHz (WB) deviation into the RX Input
connector on the rear of the radio.
Check for an audio signal @ -10dBm on pin 15 of the DB15 connector on the
rear of the MX800.
If there is an audio signal @ -10dbm check the receiver for correct SINAD,
SNR, Audio Distortion and Mute operation. Refer Section 6.3.
If there is no audio signal, inject the test signal directly into the RX module
and re-test for an audio signal on the MX800 test jig.
Replace the RX input coax cable if faulty.
Check for an audio signal on pin 2 of SKK on the Microcontroller PCB. If the
audio signal were not present then it would indicate a receiver fault, go to
section 6.3.
© SPECTRA ENGINEERING 2008 Revision 4.3.1B
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