Zenith D952X - Page 14

Chassis 4WDR50X, (X1),
Chassis 5WDR50X, (XI )
Model D583
Micro
Reverse
Micro
Reverse
Volts
AGC Voltage
Volts
AGC Voltage
Input
at Test Point "C"
Input
at Test Point "C'
0
1.50
0
.016
25
1.48
25
.012
100
1.36
100
-.037
200
1.20
200
-.124
500
1.04
500
-.312
1K
*0.96
1K
*-.470
5K
0.92
5K
-.710
50 K
0.60
50K
-3.49
100K
0.49
100K
-4.55
Chassis 15WDR50Z1
Chassis 15WDR51
Micro
Reverse
Micro
Reverse
Volts
AGC Voltage
Volts
AGC Voltage
Input
at Test Point "C"
Input
at Test Point "C'
0
1.34
0
5.00
25
1.23
25
4.20
100
0.91
100
2.80
200
0.82
200
2.40
500
0.73
500
1.70
1K
*0.70
1K
*1.10
5K
0.58
5K
0.05
50 K
0.10
50K
-2.40
100K
0.06
100K
-3.20
12
SECTION TWO
FM/MX/AM ALIGNMENT AND GENERAL INFORMATION
THEORY
From time to time Zenith includes the use of new components
and circuit applications in product design. Theory and
explanation of such components and circuits is included in
various manuals. Refer to the index for further information.
MULTIPLEX ALIGNMENT
These receivers have been properly aligned at the factory and
will not require further adjustment. As a result, it is not
recommended that any attempt be made to alter the multiplex
stages. However, should any major components in these
circuits require replacement or should anyone tamper with the
multiplex adjustments then, of course, realignment will be
necessary.
MUTING CONTROL
A muting control (some models), which supplies a reverse bias
voltage to the base of the 19KHz amplifier, is factory adjusted,
and should not require readjustment. However, if the receiver
is operated in an extremely noisy area, there is a possibility
that there may be noise bursts of sufficient magnitude to
overcome this mute voltage ... when this occurs, the Stereo 
phonic FM Indicator will light up. To further cut off the
19KHz amplifier, carefully rotate the muting control in a
clockwise direction. This should only be done when a stereo
signal is on the air since the mute control must only be
advanced to a point where the Stereo Indicator does not light
up on noise, but is should not be advanced to a point where
the desired stereo signal is cut off.
ANTENNAS FOR STEREO FM
Due to the characteristics of the stereo FM system, it will
require more signal for proper performance than does monau 
ral FM. As a result, it may be necessary to operate the stereo
FM receiver with an external antenna. The necessity for an
external antenna will be determined by the signal conditions at
each individual installation.
EXTERNAL FM ANTENNA
If the receiver is operated in an area of either low signal
strength, high noise, or where multipath (FM ghosts) signals
are present, a good external FM antenna will be required. The
necessity of an external antenna as a result of weak signal or
noise, will be quite evident since the set will not limit, and/or
noise will be quite evident. It is extremely difficult to
determine if multipath (FM ghosts) signals are present,
however, should the program material be distorted, the best
manner to decide if multipath signals are the cause of the
problem, is to connect an external FM antenna to the receiver.
Usually a TV antenna may be available for trial, but even then
the results can be misleading, since many TV antennas are of
low gain on FM frequencies. Reduction of multipath distor 
tion under high signal conditions may be accomplished by
relocation of the receivers antenna system.
FM CABINET ANTENNA
Certain models contain an FM antenna built into the cabinet.
This antenna is a folded dipole cut to the desired frequency,
and is attached to the internal periphery of the cabinet. The
following models use line cord antennas: D583, D587, C590
D593, D715, D901, D902, D903, and D904.
SIGNAL STRENGTH CHART
There are certain minimum voltages necessary for proper
stereo FM reception. To help determine if there is sufficient
signal available, the following developed AGC voltage versus
microvolt input voltage charts have been compiled. Since the
desired FM Station may not always be operating in the stereo
mode when an installation is made, these AGC voltage
measurements have been taken with a monaural FM signal.
The point of minimum AGC voltage necessary for good
stereo FM reception has been indicated on these charts.
AGC voltages are to be measured with a V.T.V.M. connected
to the following Test Points.
Chassis 4WDR50X, (XI), Model D583 - Test Point “ C ” .
Located between Transistor QI (FM-RF) and AM Antenna
(L101).
Chassis 5WDR50X, (XI) — Test Point at junction of Rl, R2,
and C3. Located adjacent to QI.
Chassis 15WDR50Z1 — Test Point €t C ” . Located between
Transistors Q101 (A.M. Converter) and Q201 (1ST. I.F.).
Chassis 15WDR51 — Test Point Q101 end of Purple wire going
around pulley end of gang.
Chassis 25WDR50, (Zl), 29CT20, 29CT21, (Zl), (Z2),
29CT30, 35WDR5O - Test Point at junction of R2, R229;
either end of purple wire at pulley end of gang.
Chassis 29AT24, (Zl), (Z2) - Test Point “ C ” RF Amplifier
AGC Feed Thru on FM Tuner.