Codan NGT 2010 RF Technical & Service Manual page 212

NGT—Checks and adjustments
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Adjusting the PA bias
Drawing
ALTERNATIVE TEXT
NOTE
To adjust the bias of the PA output FETs:
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178
If the current is out of the specified limit stated above, adjust any of the following:
• R222 (DR BIAS 1) and R235 (DR BIAS 2) fully counterclockwise (see
Figure 32 on page
• R222 (DR BIAS 1) until the current measures 20 mA ±2 mA
• R235 (DR BIAS 2) until the current measures 40 mA ±2 mA
Release PTT.
Switch off the transceiver, disconnect the multimeter, then replace the link with a
length of tinned copper wire.
08-05415 or 08-05511 (sheet 1)
The transceiver must be in Service mode to make this adjustment (see
page 154, Accessing Service
Ensure the transceiver is switched off and the DC supply is disconnected.
Disconnect the exciter output from the PA by removing the connector from J2 (Tx
coaxial) on the RF/IF PCB in the RF unit (drawing
(sheet 1)).
Unsolder the fuse PA O/P (F201) next to the power relay (DC supply to the output
FETs V215 and V216) (see
Set a multimeter to DC 10 A range and connect it in place of the removed fuse
(positive near to relay).
Connect the DC supply, then switch on the transceiver.
Select any transmit channel, then hold down PTT.
Check that the output FET current measures 4 A ±100 mA.
If the current is out of the specified limit stated above, change it by adjusting the
preset potentiometer PA BIAS (R240) (see
Release PTT.
Switch off the transceiver, disconnect the DC supply, then resolder the fuse PA O/P.
If the fuse is broken, replace it with two strands (2 × 0.2 mm TCW) taken from a
piece of 7 × 0.2 mm cable. Extend the centre of the wire down from the two stakes
to form a V, ensuring it does not touch the PCB. Solder the wire to the two stakes,
making sure the solder does not run down the strand of wire (see
page 161, PA Fuse).
162)
mode).
Figure 30 on page
Figure 30 on page
NGT Transceiver System Technical Service Manual
08-05261 (sheet 1)
161).
161).
Figure 30 on
or 08-05889