Instruction manual

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20
Section IV
CALIBRATION
“Routine” calibration of the Model 708 Stereo Generator is never
required, its digital-synthesis circuitry is simple and stable. The only
justification for confirming any of the internal adjustments is out-of-
specification operation, and only after all other possible faults have been
considered and eliminated. It’s worth a call to the factory to discuss any
anomalies before charging-ahead and possibly making things worse.
Equipment
Required
• Dual-Trace Oscilloscope — 5mV sensitivity, 20Mhz bandwidth,
with two matched 10:1 probes.
• Audio Generator — 10Hz–1MHz, +20dBm output capability.
• AC Voltmeter — with dB scaling.
• Digital Multimeter
• Frequency Counter — capable of accurate frequency
measurement from 1kHz to 2Mhz.
• “Precision” FM-Stereo Demodulator — station Mod-Monitor
with input for composite baseband signal.
• Spectrum Analyzer (optional*) — must have good resolution in
the 100Hz to 100kHz (FM composite baseband) display range.
* The Spectrum Analyzer is not required if the “Precision” FM-
Stereo Demodulator is capable of resolving crosstalk, stereo
separation and 38kHz “residual” measurements to a value of
–70dB or better.
Power Supply
Check
1. Apply power to the 708.
2. Check that the positive and negative 9-volt regulated supplies are
between 8.5V and 9.0V. You can check these on pin 8 (positive) and
pin 4 (negative) of any 8-pin IC.
Clock Set 1. Use one of the low-capacitance ‘scope probes to connect to the input
of the frequency counter. Check the clock frequency at the right-
hand end of R59, between IC15 and IC16.
2. Adjust C34, the trimmer capacitor just below the SUBCARRIER 1
input connector, for exactly 1,216,000Hz.