Receiver Section - RELM BK RADIO SDMX920 Technical Manual

MX920 Base Station & Repeater
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If the Diagnostics shows abnormal, then check the voltage on pin 95 of IC1 on
the Control Board. If the voltage is low ie <200mV then the likely fault is IC1.
If the voltage is >200mV then the likely fault is within the PA module.
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If the Diagnostics shows normal, then check the RF level from the Exciter
section by connecting a Power Meter directly to the Exciter RF connector. Using
the in-built menu system Adjust the 'Transmit Power' control to maximum, the
RF level should be >+24dBm (250mW). If not go to section 6.4.2, if so the PA is
probably faulty and go to section 6.5.
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If there is NO RF power output, check that the 'Transmit Power' control in-built
menu system 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 82 of IC1 is LOW (TP19), collector of TR19 is
LOW and pin 45 of IC1 is HIGH (TP12). If these are OK, then the Exciter or PA
may be faulty. Go to section 6.4, or section 6.5.
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Inject a 1 kHz tone @ –10dBm via pin 4 of the RJ45 connector at the front of the
radio and check for 1.5 kHz (NB)/ 3 kHz (WB) peak to peak demodulated
deviation.
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If the audio deviation is incorrect then go to the Transmitter alignment
procedure.
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If there is no audio modulation then check the audio level on pin 7, IC25B
(TP22) on the Microcontroller PCB.
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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

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Using in built menu system, selected Diagnostics, check the RXVCO locking
voltage is between 2 – 14 V and there is no RXVCO 'Unlock' alarm displayed.
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If the Rx locking voltage is out of spec then go to section 6.3.
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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.
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Check for an audio signal @ -19dBm on pin 1 of the RJ45 connector on the front
of the MX920.
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If there is an audio signal @ -19dbm check the receiver for correct SINAD,
SNR, Audio Distortion and Mute operation. Refer section 6.3.
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If there is no audio signal, Connect a RF test signal directly to the RX RF
connector and re-test for an audio signal on the RJ45 connector on the front of
the MX920.
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Replace the RX input coax cable if faulty.
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Check for an audio signal on TP1 on the Microcontroller section of PCB. If the
audio signal is not present then it would indicate a receiver fault, go to section
6.3.
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If there is a signal present at this point then it would indicate a fault with the
Microcontroller audio or mute operation, go to section 6.2.
Technical Manual
2003 Revision