NAD 4225 - STEREO DECODER, MPX FILTERS; STEREO SEPARATION AND MPX FILTER ADJUSTMENT; AM ALIGNMENTS; OSC ADJUSTMENT

DER, MPX FILTERS.
STEREO PPcoparation. Set FM generator output to 1000 uV.
eodulate FM generator left channel only and adjust R127 for minimum on
“right channel VIVM.
Modulate FM generator right channel only and adjust R127 for minimum on
left
channel
VTVM.
4.If
the
minimum
in
step
9
and
10
are
different,
adjust
R127
so
that
the
readings are the same in both channels.
5.MPX filter
Turn off audiomodulation, leaving pilot tone only. Disable IHF filter or
external 19 KHz filter if used. Adjust left channel and right channel for
minimum output.
SPECIFICATION more than 60 dB suppression.
AM ALIGNMENTS
Unless repairs have been done to Oscillator Section, do not adjust AM OSC
coil or Trimming Capacitor.
Tf OSC Adjustment is needed, connect high impedance voltmeter (preferably
DMM) between P14 and ground.
A.OSC ADJUSTMENT
1.Tune unit to show 600 kHz on display and adjust L102 to read 1.75V +0.05V
on DMM. Adjust L101 for maximum output.
2.Tune unit to show 1400 KHz on display and adjust L101 for maximum output.
3.Repeat step 1 and 2 until no further improvement.
B.IF ADJUSTMENT
1.For IF adjustment and Tracking adjustment connect VIVM to loudspeaker
output (or tape output), only one channel connection needed, and connet
signal generator to antenna terminals. Adjust generator for 30% modulation
and approx. 10 uV input(DIRECT). Tune both generator and receiver to
approx. 100 KHz, and adjust generator frequency for maximum reading on
VIVM. Than adjust I101 for maximum reading on meter.
C.TRACKING ADJUSTMENT
1.Tune unit and generator to show approx. 600KHz and adjust L101 to maximum
reading on VIVM.
°.Tune unit and generator to show approx. 1400KHz and adjust C138 (Trimming
Capacitor) for maximum reading on VTVM.
3.Repeat step 1 and 2 until no further improvement.