8525B/8528 Technical Service Manual Adjustments 7-13
Publication No: 15-02036 Issue 6
7.3.15 Options SD, SDE and SDEM
With these options fitted the oscillator frequency of the phase locked loop
on the Selective Call PCB must be set up as follows:
1. Apply a 1775Hz sine wave at 1.0Vpp to pin 2 of J1 on the Selective
Call PCB. (Pin 3 ground.)
2. Connect a dc voltmeter between TP2 and TP3 of the PCB. (Polarity
may be either way, connect so that meter deflection is forward.)
3. Adjust R15 for 0V ±50mV deflection of the voltmeter.
7.3.16 Option TD
With this option fitted the Two-tone Decoder PCB can be set up, if
necessary, as follows:
1. Using the table on Drawing 04-02231 select values for R25, R26 and
R31 appropriate to the frequency nearest the nominated difference
frequency to which the Two-tone Decoder is to respond. Connect these
into the appropriate locations.
2. Connect a high-impedance frequency counter via a 100kΩ resistor to
TP4 on the Two-tone Decoder PCB.
3. Disconnect J2 (Audio input).
4. Switch on power to the unit and observe the frequency counter. Adjust
R30 on the Two-tone Decoder PCB for an indicated frequency within
2Hz of the nominated difference frequency.
Note: If the nominated frequency cannot be obtained within the range
of R30, coarse adjustment can be made by selection of the value
of R32.
5. Reconnect J2.
6. Arrange for the reception of two-tone calls with various difference
frequencies and ensure that the transceiver responds to only those calls
which contain the nominated frequency difference.
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