Codan NGT 2010 RF Technical & Service Manual page 553

Adjusting the power amplifiers (3061/3062)
Replacing output transistors
Drawing
08-05978 (sheet 3)
CAUTION
Adjusting the amplifier bias
Drawing
NOTE
To adjust the amplifier bias:
1
1
1
1
1
1
1
1
1
NGT Transceiver System Technical Service Manual
08-05977 (sheet 1)
If any of the output transistors on the Power Amplifier PCBs need to be
replaced, all of the transistors must be replaced with a set of transistors of
the same gain. The gain is indicated by a letter or colour marking on the
device body.
08-05977 (sheet 1)
The transceiver does not have to be in Service mode to perform this
adjustment.
Ensure there is no audio drive to the NGT and disconnect the RF drive between the
NGT and the amplifier.
Connect a DC millivoltmeter across one of the 2-pin headers associated with the
current sense resistors on the Power Supply PCB.
Adjust the bias preset potentiometer on each Power Amplifier PCB fully
counterclockwise.
Switch on the NGT, hold down PTT, then adjust the relevant amplifier's bias preset
potentiometer until the meter reads 2 mV (representing a bias current of 400 mA).
Check that the voltage across the other 2-pin header of the same Power Supply PCB
is 2 mV.
Release PTT.
Check the other Power Supply PCB/Power Amplifier PCB pair (3062 only).
Switch off the NGT.
Reconnect the RF drive.
and drawings 08-05978 (sheet
High power—Fault finding and adjustments
1), 08-05978 (sheet 2) and
239