NGT—Checks and adjustments
NGT Transceiver System Technical Service Manual 179
To adjust the bias of the PA output transistors:
1 Ensure the transceiver is switched off and the DC supply is disconnected.
1 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 08-05261 (sheet 1) or 08-05889
(sheet 1)).
1 Unsolder the fuse PA O/P (F201) next to the power relay (DC supply to the output
transistors V211 and V212) (see Figure 31 on page 162 or Figure 32 on page 162).
1 Set a multimeter to DC 1 A range and connect it in place of the removed fuse
(positive near to relay).
1 Connect the DC supply, then switch on the transceiver.
1 Select any transmit channel, then hold down PTT.
1 Check that the output current measures:
• 400 mA ±50 mA for 08-05869, or
• 400 mA ±20 mA for 08-06461
If the current is out of the specified limit stated above, change it by adjusting the
preset potentiometer PA BIAS (R239) (see Figure 31 on page 162 or Figure 32 on
page 162).
1 Release PTT.
1 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 Figure 31 on
page 162 or Figure 32 on page 162, PA Fuse).
ALTERNATIVE TEXT
Drawing 08-05869 (sheet 2) or 08-06461 (sheet 2)
NOTE
The transceiver must be in Service mode to make this adjustment (see
page 154, Accessing Service mode).
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