NAD 7155 - FM Alignments; Tuning Voltage (Oscillator); RF Adjustment (Tracking); IF Adjustment

FM ALIGNMENTS
NECESSARY INSTRUMENTATION
FM GENERATOR (less than 0.05% THD)
STEREO GENERATOR (less than 0.05% THD, more than 50 dB sep.)
AUDIO GENERATOR (not necessary if FM generator has built in sweep; ie, SOUND TECHNOLOGY ST 1000A and
ST 1020A)
AC VTVM's (or one with a left/right switch)-
THD ANALYZER (resolution less than 0.1%)
OSCILLOSCOPE (5mV or better sensitivity, X input capability)
FREQUENCY COUNTER
VOM or DMM (high impedance, must read in mV)
DETECTOR PROBE
IMPORTANT
FRONTEND
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While all FM generator output levels hereafter are referred to the 300 ohm input, 75 ohm input
can be used, but be aware of possible equipment groundloops and divide the RF output levels
by 2.
Before alignments commence set input selector and record selector to tuner and release mono
dyn sep defeat switches (out).
Alignment of frontend should only be necessary after repair to frontend or crystal oscillator
circuits (pin 2 and 3 on IC 110).
TUNING VOLTAGE (OSCILLATOR)
It is essential to check tuning voltage before aligning the rest of the frontend.
Connect DMM between ground and TP 102.
Tune to 108 MHz and adjust C 20 if voltage is incorrect.
SPECIFICATION 24.7V + 0.5V
Tune to 88 MHz and read voltage. Adjust L 6 if voltage is incorrect.
SPECIFICATION 3.6V + 0.5V>
Repeat step 2 and 3 until readings are within tolerances.
RF ADJUSTMENT (TRACKING)
Connect RF generator to 300 ohm antenna input and detectorprobe to pin 1 IC 102 with ground to
tunershield. Adjust sensitivity of oscilloscope to maximum (SmV or better) and modulate FM generator
sweep * 300 kHz or more.
Set tuner to 105 MHz, enter into preset 5, and tune generator so that curve appears on oscilloscope.
Turn down RF input level so that curve covers approximately 1/2 of oscilloscope display.
Adjust C 3,C 9, C 11 and C 15 to maximum curve height while reducing RF input to keep entire curve
on display.
Set tuner to 90 MHz, enter into preset 1, and tune generator so that curve appears on oscilloscope display.
Adjust L 1, L 2, L3 and L 4 to maximum curve height.
Repeat steps 2, 3, 4 and 5 (use preset 1 and 5) until both frequencies are at maximum curve height.
NOTE: 105 MHz curveheight is typically slightly stronger than 90 MHz.
IF ADJUSTMENT
Set tuner to approximately 98 MHz (the tuner must be tuned to an unoccupied frequency) enter into
Preset 3, and tune FM generator to display a curve on oscilloscope.
Adjust L 5 and L 101 to maximum and symmetrical curve on the display, using as little input as
Possible.
NOTE: Maximum input 500 yV, typical curveheight 4 mV at 150 uV and 15 mV at 300 nV.
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