DAEWOO CN-200A CHASSIS Repair Manual

10. PICTURE IF/AFT ADJUSTMENTS
NOTE: THIS RECEIVER IS TRANSISTORIZED AND SPECIAL CARE MUST BE TAKEN WHEN SERVICING. READ
THE FOLLOWING (NOTES BEFORE ATTEMPTING ALIGNMENT)
Alignment requires an exacting procedure and should be undertaken only when necessary.
Isolation transformer must be used to prevent shock hazard.
The test equipment specified or its equivalent is required to perform the alignment properly. Use of equipment which
does not meet these requirements may result in improper alignment.
Accurate equipment is essential to obtain proper alignment of this receiver.
Use of excessive signal from a sweep generator can cause overloading of receiver circuit Overloading should be
avoided to obtain a true response curve. Insertion of markers from the marker generator should not cause distortion of
the response curve.
The AC Power line voltage should be kept 120 volts while alignment is being performed.
Do not attempt to disconnect any components while the receiver is in operation.
Make sure the power cord is disconnected before replacing any parts in the receiver.
TEST EQUIPMENT
Digital voltmeterNational Model VP-2600A or equivalent
OscilloscopeTektronix Model 2215A or equivalent.
Direct/Low-capacity probeTektronix Model P6120 or equivalent
(Accessory of oscilloscope)
Color-Bar/Dot/Crosshatch generatorTektronix Model 146 or equivalent.
PIF sweep marker generatorNihon Tsushinki Model 4723 or equivalent
Power supplyAcademy Model 150A or equivalent
Isolation transformerVoltage adjustable type having capacity of
at least 150 watts
BLOCK DIAGRAM
MAIN BOARDOSCILLOSCOPE
B+
BIAS
TP3TP7
POWER
SUPPLY
TP6
A
TP5XY
(12V)
45.75MHz
AGC
Fig. 6 PIF Response
BIASPIF SWEEP/MARKER GEN.
POWER
SUPPLY
B
(4-5V)
VHDETINOUT
P 45.75MHz
Fig. 5 Picture IF Sweep AlignmentFig. 7 AFT Response Curve
1) Disconnect the TUNER IF output from TP6 and connect equipment as shown above.
2) Set the sweep/marker generator for 30 Vrms.
3) Observe 1 Vp-p on scope by adjusting power supply B (4~5V).
4) Adjust PIF coil L505 for according beat signal with 45.75 MHz marker on scope (See Fig. 6).
5) Connect the DET IN to TP7.
6) Adjust AFT coil L504 for center display at 45.75 MHz on scope (See Fig. 7).
7) After completing the above steps, disconnect equipment and adjust the AGC delay circuit as explained in the General
Adjustments section of this manual.
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