User Manual

SGD-SB2025NT-TUM, Part 1
Jan 12 Page 62 FAULT FINDING
4. With PTT ON, measure the PA bias current at the gates of the FETs. The bias current is
band dependent. This is done by monitoring the current drain of the whole PA with CN1
disconnected. Link the gate of TR2 to GND. Measure current consumption (VHF High Band
200 mA, VHF low and UHF 400 mA). This can be adjusted by RV2. Measure gate volts
≈ 3.4 V.
5. Remove the link from TR2. Measure the current consumption and adjust RV1 so that current
is 2 Amp total (VHF & UHF) and VHF Low 1 Amp. Measure gate volts ≈ 3.9 V.
6. Using a coax lead, connect the RF output connector CN3 to a power meter. Turn on the
supply voltage and the signal generator RF output. PTT the PA and increase the generator
output (do NOT exceed +24 dBm) whilst measuring the output power output (≥50 watts @
+24 dBM).
7. If the output power is low, turn the supply voltage OFF and lift one side of the capacitors
connecting to the directional coupler and solder a flying lead to the lifted side. Connect the
earth of the flying lead to the earth of the PA. Connect the power meter to the flying lead.
8. Turn on the supply voltage and the signal generator RF output. PTT the PA and increase the
generator output (do NOT exceed +24 dBm) whilst measuring the output power output
(≥55 watts @ +24 dBM).
9. If all the above tests fail, TR1 or TR2 may be faulty. Contact Simoco Customer Services and
arrange for the PA to be returned to Simoco’s Service Centre.