Fisher MC-715 - FM TUNER ALIGNMENT; FM IF S-CURVE ALIGNMENT; FM RF TRACKING ALIGNMENT; DETECTOR ADJUSTMENT (MINIMUM T.H.D.)

FM TUNER ALIGNMENT |
FM ALIGNMENT — FUNCTION switch to FM STEREO
Standard test frequency 1 kHz and deviation +75kHz
ITEM GENERATOR ‘| DIAL SETTING INDICATOR PROCEDURE
Note: The FM IF circuit utilizes a non-turnable ceramic filter which establishes the IF bandpass. To insure symmetrical
turning and selectivity, the IF must be aligned precisely to the center of the filter bandpass, rather than to 10.7MHz
as in conventional LC circuits.
1. FMIF Connect 10.7MHz Radio | Position of Connect Radio IF Adjust FM IFT (T1) and FM DET
S-CURVE IF Genescope output to | non-interference Genescope input | Coil (T2) until the S-curve
ALIGNMENT TP1 and ground terminal.) Minimum to TP2 and ground | becomes symmetrical and
Use 10~20pF Capacitor | Frequency. terminal. _| Straight.
in series with generator
lead.
. FRONT END Tuning knob fully Place center of dial pointer on “0”
ALIGNMENT counterclockwise. (zero) and secure pointer with
bonding material.
. FM RF Connect FM RF Signal Center of 87MHz Connect AC VTVM, | Adjust FM OSC Coil (L6) and FM
TRACKING Generator through FM calibration mark Distortion Meter ANT Coil (L5) for best curve form
ALIGNMENT Dummy Antenna toFM on dial. and Oscilloscope j|.and minimum distortion.
(87MHz) Antenna terminals. to TP2 and ground
Set generator to 87MHz. terminal.
Modulate with 1kHz to
provide +75kHz
deviation.
Set generator output
with attenuator as low
as possible.
4. Change generator Center of 1\O9MHz | Sameas above. . Adjust FM OSC Trimmer (TC2)
(109MHz) Setting to 109MHz. calibration mark and FM ANT Trimmer (TC1) for
on dial. best curve form and deflection.
Note: Repeat Items 3 and 4, and confirm that Tracking Error is minimized and best sensitivity is obtained at each frequency
point. Then, set generator to 98MHz and confirm that the pointer is correctly set on the dial plate.
. DETECTOR Connect FM PF Signal Center of 98MHz Connect Harmonic | Adjust FM DET (T2) for minimum
ADJUST- Generator to FM ANT calibration mark Distortion Meter gain and best linearity.
MENT terminals. on dial. and Oscilloscope
(MINIMUM Set generator output to TP2 and ground
T.H.D.) level to 60GB at terminal.
98MHz +2kHz.
. PLL IC Same as above. Same as above. Connect 3900 Adjust VR1 in multiplex circuit
FREE RUN Resistor and Fre- to obtain 38kKHz +200Hz on
FREQUENCY quency Counter Frequency Counter.
ADJUST- between IC5 (Pin
MENT No.6) and ground
(19kHz) terminal.
Use a screwdriver with plastic grip for all adjustments.
=4g—