User Manual

SGD-SB2025NT-TUM, Part 1

Jan 12 Page 61 FAULT FINDING

7. Adjust T1 and T2 for minimum distortion <1%.

8. If the distortion is high, FL3A, FL3B or FL4 may be faulty.

9. If the sensitivity is still poor, contact Simoco Customer Services and arrange for the Module

to be returned to Simoco’s Service Centre.

7.4 E

XCITER

ODULE

7.4.1 VCO Locking

1. On the Exciter module, check the reference frequency of X3 (13 MHz or 14.4 MHz) is the

same as the Tx Reference Frequency in the ‘Hardware Settings’ on the MxTools

configuration menu.

2. On the Micro Controller PCB, connect a DVM to the ‘TX VCO’ test point and check the Tx

locking voltage is between 2 V – 18 V.

3. Check that +12 V (SKD-2) and 28 V (SKD-13) supply lines are present.

4. If the Tx locking voltage is out of specification, on the Tx VCO, slowly adjust CT1 a full 360°

and check for a change in the locking voltage.

5. If there is a change in the Tx VCO locking voltage, realign the VCO voltage to 9 V at centre

frequency of the VCO frequency band.

6. If there is no change in the Tx VCO locking voltage, check the VCO supply voltage at SKU-3

is approx. 7 V and, with an Oscilloscope, check the TCXO is oscillating on pin 8 of IC 10.

7. If all the above tests pass, the VCO or IC10 may be faulty. Contact Simoco Customer

Services and arrange for the Exciter Module to be returned to Simoco’s Service Centre.

7.4.2 RF Power

1. Using MxTools increase the ‘Transmit Power’ control to maximum and check that the output

power is greater than +24 dBm.

2. If the Exciter power is low, check for the +8 V supply voltage at the outputs of IC2 and TR4.

3. Use a RF probe to check for gain through IC2 and TR4.

4. Lift R2 and solder a flying lead to the junction of R1 and R2. Check the output power of the

VCO is between 0 and +3 dBm.

5. If all the above tests pass, contact Simoco Customer Services and arrange for the Exciter

Module to be returned to Simoco’s Service Centre.

7.5 P

OWER

MPLIFIER

1. Firstly, carry out a visual inspection of all the components on the PA looking for any

damaged components.

2. Connect the input of the PA to signal generator with the RF output switched off.

3. With PTT off, measure the +13.8 V supply at the source of the driver and output FET. If out

of specification, check voltage at CN2-2, if no volts check the supply cable.