WhitakerAudio AM/FM Stereo Tuner 2012, Assembly & User Manual, Page: 133 / 166

133
AM/FM Stereo Tuner
– Adjust coil L57 for maximum output as indicated on the voltmeter and oscilloscope. Note
this coil will be very broad and the slug will probably have to be rocked back and forth to
find the peak. The voltmeter should read about 7 V rms.
The foregoing procedure will bring the multiplex adapter very close to ideal alignment. If a
frequency counter is available, the following additional steps should be taken to precisely align
the oscillator section.
– Switch the tuner off.
– Connect the scope, voltmeter, and frequency counter to the junction of D51/D52/R92/R94
( Test Point C ).
– Set the signal generator to 19 kHz; confirm with the frequency counter. Adjust so the
frequency is as close to 19.00 kHz as possible. Adjust the generator output level to 0.1 V
rms.
– Switch the tuner on.
– While monitoring the frequency counter and voltmeter, adjust L54 so the displayed
frequency is as close to 38.00 kHz as possible. While making this adjustment, the output
voltage may decease slightly.
– Adjust T55 for maximum output as indicated on the voltmeter. The displayed frequency
should not change. This adjustment should return the voltage to about 7 V rms.
– Confirm that the 38 kHz oscillator is properly locking to the 19 kHz pilot signal. Take note
of the frequency displayed on the counter. Disconnect the 19 kHz input signal and note
that the displayed frequency changes. The difference may be small or significant
(anywhere from a few Hz to 100 Hz is common). Reconnect the 19 kHz signal and
confirm that the 38 kHz oscillator returns to its previously noted position.
– Switch the tuner power off.
– Set the signal generator to 1 kHz and adjust its output level to 3 V rms.
– Remove the scope and voltmeter leads from Test Point C.