User Manual

SGD-SB2025NT-TUM, Part 1
Jan 12 Page 59 FAULT FINDING
7. If the Diagnostics shows abnormal, on the Motherboard, check the voltage on pin 62 of IC1.
If the voltage is low (i.e. <200 mV), the likely fault is IC1. If the voltage is >200 mV, the likely
fault is within the PA module.
8. If the Diagnostics shows normal, check the RF level from the Exciter module by connecting a
Power Meter directly to the Exciter RF connector. In MxTools, adjust the ‘Transmit Power’
control to maximum, the RF level should be >+23 dBm (200 mW). If the RF level is correct,
the PA is probably faulty, go to Section 7.5. If the RF level is not correct, go to Section 7.4.
9. If there is No RF power output, in MxTools, check that the ‘Transmit Power’ control has not
been set to 0 (zero) or 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, the Exciter or PA may
be faulty. Go to Section 7.4, or Section 7.5.
10. Using the Engineering Terminal, inject a 1011 Hz tone @ –4.4 with route set to ‘External.
11. If the audio deviation is incorrect, go to the Tx alignment procedure in Section 6.
12. If there is no audio modulation, check the audio level on pin 13, IC11on the Micro Controller
PCB.
13. If there is no audio on the above test point, go to Section 7.2, otherwise, go to Section 7.4.
7.1.2 Receiver Section
1. Using MxTools Diagnostic’s, check the Rx VCO locking voltage is between 2 V – 18 V and
there is no Rx VCO ‘Unlock’ alarm displayed.
2. If the Rx locking voltage is out of specification, go to Section 7.3.
3. Inject a –60 dBm RF test signal at the Rx frequency and modulated with a 1 kHz tone @ 1.5
kHz (NB)/3 kHz (WB) deviation into the Rx input connector on the rear of the radio.
4. Check for an audio signal @ -10 dBm on pin 15 of the DB15 connector on the rear of the
SB2025.
5. If there is an audio signal @ -10 dbm, check the Rx for correct SINAD, Signal to Noise Ratio
(SNR), Audio Distortion and Mute operation. Refer to Section 7.3.
6. If there is no audio signal, inject the test signal directly into the Rx module and re-test for an
audio signal on the SB2025 test jig.
7. Replace the Rx input coax cable if faulty.
8. Check for an audio signal on pin 2 of SKK on the Micro Controller PCB. If the audio signal is
not present, it indicates a Rx fault, go to Section 7.3.
9. If there is a signal present at this point, it indicates a fault with the Motherboard audio or mute
operation, go to Section 7.2.
7.2 M ICRO C ONTROLLER PCB
1. Check the fuse. If blown, replace with a 5x20 mm 3 A fast blow fuse.
2. Check all jumpers and switch settings are in the correct position for your requirements.