Zenith MC7041 - Page 17

RF, IF AND MPX ALIGNMENT PROCEDURE
FOR MODEL MC7051 - Cont'd.
STEP
CONNECT
GENERATOR
TO
DUMMY
ANTENNA
CONNECT
VTVM/
SCOPE TO
INPUT
SIGNAL
FREQ.
SET DIAL
TO
ADJUST
PURPOSE
FM ALIGNMENT
Note: For FM IF Alignment Use A Signal Of 250 KHz Deviation, 50 Hertz Modulation For Full Bandpass Display. Bandswitch In FM. Preset R208,
R21 1 And R303 To Mid Rotation Before Connecting Generator. Connect Generator Cable Ground To Gang Frame.
32
Shunt C1B To Ground With A .001 MF Capacitor.
33
Test Point "D"
FM IF Input
At High Side
Of C1F
Generator
Output
Probe "A"
Scope
Detector
Probe "C"
Test Point
At IC201
Pin 1.
10.7 MHz Gang
Closed
Align I.F. Transformer For
Maximum Output And Symmetry
As Indicated In Scope Pattern "A".
34
Test Point "D"
FM IF Input
At High Side
Of C1F
Generator
Output
Probe "A"
Scope
Detector
Probe "C"
Test Point
At IC201
Pin 1.
Tune Generator To Center Total Bandpass
Waveform. Do Not Change Generator Frequency
For Remainder Of FM IF Alignment.
Align I.F. Transformer For
Maximum Output And Symmetry
As Indicated In Scope Pattern "A".
35
Test Point "D"
FM IF Input
At High Side
Of C1F
Generator
Output
Probe "A"
Scope
Detector
Probe "C"
Test Point
At IC201
Pin 1.
Center Freq.
Of Ceramic
Filters Y201,
Y202, Y203
Gang
Closed
T1
Align I.F. Transformer For
Maximum Output And Symmetry
As Indicated In Scope Pattern "A".
36
Test Point "A"
FM Antenna Post
(Disconnect Antenna)
300 Ohm Scope
Test Point
"H"
98 MHz
98 MHz R216
Adjust For No Sound Output
When Input Is Below 1.7/iV With
Mute Switch ON.
37
Test Point "A"
FM Antenna Post
(Disconnect Antenna)
300 Ohm Scope
Test Point
"H"
98 MHz
98 MHz
R215
Adjust For A Reading Of 4 To 5
One Meter M1 02 With Input Of
60dBV (1mV).
NOTE: For FM Detector Alignment Use A Signal Of 75 KHz Deviation, 1 KHz Modulation. Also Connect Generator Modulation Frequency To
Scope Horizontal. Adjust Generator IF Frequency To Center Total Bandpass Waveform. Do Not Change Generator IF Frequency For
Remainder Of IF Alignment. (If Your Generator Does Not Provide Output For Audio Modulation Frequency Use Horizontal Output From
Generator, Or Scope Horizontal Sweep, And Follow Step 38C). Minimum Distortion Can Only Be Achieved By Use Of Step 38A Below.
38
Test Point "D"
FM IF Input
At High Side
Of C1F
Generator
Output
Probe "A"
A. Distortion
Analyzer
(Thru A 100
Usee De-
emphasis
Network)
Probe "B"
And Scope.
B.Scope
C.Scope
Center
Frequency
Of Ceramic
Filters Y201,
Y202, Y203.
Gang
Closed
L204, L205
(T201)
A. Preferred Method: Distortion
Analyzer At Test Point "H"
Should Read Minimum Distortion.
B. Alternate Method: Adjust For
Linear Scope Trace-No Curve At Ends
Of Trace. Disregard Meter Reading.
C. Alternate Method: Adjust For
Maximum Length And Symmetry,
Similar To Scope Pattern "A".
39
Test Point "D"
FM IF Input
At High Side
Of C1F
Generator
Output
Probe "A"
Test Point
"H"
Center
Frequency
Of Ceramic
Filters Y201,
Y202, Y203.
Gang
Closed
L205
Adjust For Center Reading On
Tuning Meter M101.
40 Test Point "A"
300 Ohm
106 MHz 1 06 MHz
C1H
Set Oscillator To Dial Scale.
41
FM Antenna Post
(Disconnect Antenna)
300 Ohm
90 MHz 90 MHz
L7
Set Oscillator To Dial Scale.
42
FM Antenna Post
(Disconnect Antenna)
300 Ohm
Repeat Steps 40 & 41 For Minimum Change.
Set Oscillator To Dial Scale.
43
FM Antenna Post
(Disconnect Antenna)
300 Ohm
106 MHz 1 06 MHz
C1D, C1F
Align FM Detector Stage For
Maximum.
44
FM Antenna Post
(Disconnect Antenna)
300 Ohm
90 MHz 90 MHz L3, L4
Align FM Detector Stage For
Maximum.
45
FM Antenna Post
(Disconnect Antenna)
300 Ohm
106 MHz 106 MHz
C1B
Align FM Antenna Stage For
Maximum.
46
FM Antenna Post
(Disconnect Antenna)
300 Ohm
90 MHz
90 MHz
L2 If Necessary
Align FM Antenna Stage For
Maximum.
47
FM Antenna Post
(Disconnect Antenna)
300 Ohm
Repeat Steps 43 Thru 46 For Minimum Change.
48 Audio Osc.
—
Test Point
"F"
200 KHz
T301
Align For Minimum.
49
Test Point "H"
—
Test Point
"F"
200 KHz
T302
Align For Minimum.
NOTE : Apply Sufficient Signal Level — Approx. 1 00 Microvolts — To Obtain Full Limiting At Point Near 98 MHz.
50
Frequency
Counter And/
Or Scope
Test Point
"M"
Unmodulated
RF Carrier
R308
A. Frequency Counter Should
Read 19 KHz, + 100 Hz.
B. Alternate Method: Connect Test
Point "M" Signal To Scope Vertical
And An Accurate 19 KHz Signal
To Scope Horizontal Input. Adjust
For One Square Synchronized
Waveform.
51
Scope And/Or
AC VTVM
Left Tape
Output
98 MHz
1 0% Pilot
(L+R) (L-R)
(L Only)
R318
Adjust For Separation.
Maximum Left Output.
52
Right Tape
Output.
98 MHz
1 0% Pilot
(L+R) (L-R)
(L Only)
—
Check For Separation. Minimum
Right Output.
NOTE: Do Not Readjust Control R308 After Step 50.
CERAMIC FILTERS
COLOR
CODE
NOMINAL CENTER
FREQUENCY
FREQUENCY
RANGE
Black
10.64 MHz 10.61 to 10.67 MHz
Blue 10.67 MHz
10.64 to 10.70 MHz
Red
10.70 MHz
10.67 to 10.73 MHz
Orange 10.73 MHz
10.70 to 10.76 MHz
White
10.76 MHz
10.73 to 10.79 MHz
15