8525B/8528 Technical Service Manual Adjustments 7-11
Publication No: 15-02036 Issue 6
8528S
If the transceiver is fitted for LSB operation:
1. Select a channel with LSB mode enabled.
2. Connect the frequency counter, via a high impedance (x10) probe, to
the inner conductor of the Local Oscillator cable on the RF Mixer and
Dual Synthesizer PCB.
3. Adjust C162 for 1647kHz 1Hz indication on the counter.
4. If the range of C162 is insufficient C161 may be altered to compensate.
7.3.12 Mute Adjustment
1. Connect the transceiver to an antenna (a short length of wire will
suffice) and select an unoccupied channel.
2. Press the Audio Mute pad (8525B), or the Mute On/Off pad (8528), to
get the Mute indicator lit.
3. Begin with R73 on the Audio and IF 1650kHz PCB fully anti-clockwise
and slowly rotate the control clockwise until the mute audio gate opens.
4. This is the threshold of mute operation. In order to reduce the
sensitivity, rotate the control anti-clockwise 1/4 turn.
5. The mute circuit should now be sensitive enough to detect weak signals
without false triggering on noise pulses. However, if desired, the
sensitivity may be varied from this setting to suit individual
requirements.
7.3.13 PA Adjustments
Disconnect the dual coax socket from the PA and Filter PCB.
Driver Bias
1. On the PA and Filter PCB (08-03743) remove the link feeding the
centre tap of T3 primary and replace with an ammeter set to read 10 to
20mA.
2. Select on test a value for R46 for a current reading between 10 and
15mA with the microphone PTT switch pressed.
3. Remove the ammeter and re-install the link.
PA Bias
1. Remove link marked ‘PA’ on the PA and Filter PCB (F2 on circuit
diagram 04-02452).
2. Replace link with an ammeter set to read 100 to 200mA.
3. Adjust R48 for a current reading between 100 and 150mA with the
microphone PTT switch pressed.
4. Remove the ammeter and re-install the link.
5. Reconnect the dual coax socket.
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