NAD 7020e - FM Detector and MPX Alignment; Detector Coarse and Final Alignment; Autosearch Level Adjustment; Stereo Decoder and MPX Filter Adjustments

D.
DETECTOR COARSE ADJUSTMENT (OPTIONAL,NEEDED ONLY IF DETECTOR WAS REPAIRED).
Reduce sweep modulation level to +/- 75 kHz and set input level to 300 uv.
Adjust FA generator frquency so that both legs of the inverted U-shaped curve are equally high on the display.
The curve should be almost perfectly symmetrical.
Disconnect detectorprobe from tuner and oscilloscope. Connect either of the tape rec. outputs to the
oscilloscope.
Adjust I 102 primary (closest to the rear of unit) to maximum curveheight and I 103 secondary (closest to the
front of unit) to minimum curveheight and straightest possibe line. Go back and forth between primary and
secondary till both-are peaked.
NOTE: Both the cores should be within 1.5 mm from the top of the form,
DETECTOR ALIGNMENTS (FINAL)
Disconnect detectorprobe and connect tape rec. outputs to VTVM's, oscilloscope and distortion analyzer.
Switch stereo generator to 1 kHz 100X(+/- 75kHz) mono modulation and oscilloscope to normal internal sweep 0.2 mS
“and 0.5 V/cm sensitivity.
Detector reference frequency
Reduce FM generator output level while monitoring THD from left channel. When THD increases to 3%, fine tune the
FM generator frequency to minimum THD, Reduce FM generator output level and fine tune till no reduction in the
3% THD can be achieved by fine tuning. Use this frequency for all the following detector, MPX and FM NR
adjustments.
NOTE: The typical input level for this 3% THD should be 1.6 uv to 2.3 uv. This is done only to “lineup” the
NOTE:
1,
2.
frequency from the generator to the tuner’s frequency. If IHF usable sensitivity (-30 dB THD+N= 3.16% THD+N)
is to be verified, a proper IHF bandpassfilter must be used.
Connect DMM ACROSS P112 (negative) and P113 (positive). Set FM generator output level to 1000 wv.
Adjust I 102 primary (closest to the rear of unit) for 0 V on DMM.
TOLERANCE +/- 50 mV
Adjust I 103 secondary (closest to the front of unit) for lowest THD.
SPECIFICATION less than 0.1%.
Repeat steps 5 - 7 till no further improvements. Record the DMM’s final reading for use later in the
adjustment.
AUTOSEARCH LEVEL
Connect DMM between 117 and ground.
Increase FM generator level SET TO 10 uY and adjust R117 so that DMM reading goes from 8.5 V to approximately
0.554 at 10 uv.
TOLERANCE +/-0.15v
STEREO DECODER, MPX FILTERS.
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VCO
Connect a frequency counter between IC 6 pin 11 and ground.
Set FM generator to 1000 uv output and no modulation,
Adjust VR 3 for a 19000 Hz reading on the counter.
TOLERANCE +/- 100H2
Disconnect frquency counter and press FM NR. defeat switch (inj.
Stereo switch threshold.
Modulate FM generator 1 kHz 45% left only plus 19 KHZ PILOT 8 - tOX.
Increase FM generator level upwards from 0 and adjust VR 2 so that stereo light turns on and audio outputs
as watched on VTVM and oscilloscope, switches to one channel only at 10 uv input level.
TOLERANCE +5 uv
When turning input level down the unit will switch into mono at a lower level, typically 5 - 7 u¥.
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