NAD 7225PE - Page 3

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FM ALIGNMENT
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NECESSARY INSTRUMENTATION :
FM SIGNAL GENERATOR (<_ 0.03% THD) _
STEREO MODULATOR (< 0.03% THD)
50/75 OHMS DUMMY ANTENNA (If needed by generator)
DIGITAL VOLTMETER (DVM)
DISTORTION METER (< 0.1% resolution)
AC VOLTMETER
OSCILLOSCOPE (< 5 mW sensitivity)
IHF FILTER
ONOOhRWNM >
. IMPORTANT NOTES
All equipment must be capable of measuring better than specification of unit under test.
2. 1KHz modulating signal, +75 KHz deviation, mono unless otherwise stated. | |
3. All RF levels quoted are at 75 OHMS impedance. If at 300 OHMS impedance, add 6 dBu from figures.
4. Enter the following frequencies: 98, 87.5 , 108, 90 and 106 MHz.
PREPARATION
1. Turn Ht (IF) counterclockwise until core is near the top.
2. Turn 1102 (FM detector primary) counterclockwise until core is near the top.
3. Turn 1103 (FM detector secondary) counterclockwise until core is near the top.
PROCEDURE
. OSCILLATOR TUNING VOLTAGE
1. Connect DVM between P123 and ground.
2. Set tuner to 87.55 MHz and check DVM for a reading of 3 VDC + 05V.(1.6 VDC + O.3V for C1 version).
3. Set tuner to 108 MHz and check DVM for a reading of 205 VDC + O5V (8 VDC + O.5V for C1 version).
If either of the above is out of tolerance, adjust L8 (oscillator coil) until both readings are within tolerance.
. IF CENTER ADJUSTMENT
Connect DVM between P112 and P113.
Apply 10.7 MHz (90 dBu) VIA 1K OHM resistor to P111.
Adjust 1102 (cilcckwise) for 0 VDC + 50 mV reading on DVM.
Adjust 1103 (clockwise) until minimum THD is achieved at audio O/P.
Repeat (3) and (4) until no further improvement can be made.
NOTE: When adjusting 1103 two nulls can be fund: Adjust until the second one is found as this has lower THD. Correct position of core
is normally just above the metal! Seeing: |
~ SYNTHESIZER / IF TRACKING.
Maintain connection of DVM and disconnect 10.7 MHz TAP at P41. - _— 3 .
1.
2. Apply 98 MHz (54dBu) to 75 OHMS antenna input and tune to 98 MHz.
3. Adjust C917 forO VDC + 20 mV reading on DVM.
4. Fine adjust 1103 for minimum THD.
5. Repeat (3) and (4) until no further improvement. can be made.
11 ALIGNMENT |
1. Connect DVM between wiper of R117 (right of R159) and ground.
2. Turn A117 fully counterclockwise.
3. Apply 98 MHz (6dBu) to antenna input.
4. Carefully adjust {1 to obtain maximum reading on DVM. There should only be one maximum.
RF ADJUSTMENT
1. Apply 98 MHz (6dBu) to antenna input.
2. Check if THD is better than 3%. If not, proceed to (3).
3. Adjust L2, L4 and L5 by squeezing or stretching using a non-metallic tool until THD is better than 3%.
4. Repeat (3) at 90 MHz and 106 MHz and re-adjust until THD is within 3% at 7dBu for both frequencies and 6 dBu for 98 MH: s
AU TOSEARCH LEVEL
1. Connect DVM between wiper of R117 (right to R159) and ground.
2. Apply 98 MHz (60dBu) to antenna input and tune to 98 MHz.
3. Adjust R117 to get 1.05 VDC + 0.01 V reading on DVM.
4. Check if autosearch operation is working properly at antenna signal level of 26dBu (20uV).
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ee SEPARATION AND PILOT SUPPRESSION
Modulate L-only at 98 MHz (60d8u) and adjust R127 for minimum output on right channel.
Modulate R-only and adjust R127 for minimum output on left channel.
Repeat (1) and (2) until readings are the same and within specs.
Cancel stereo modulation and leave pilot tone.
Adjust Z105 and Z106 for minimum output on left and right channels, ‘respectively.
MPaON =
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