Alignment Procedure; Required Instruments; Fm 10.7Mhz Alignment; Fm Front End Alignment - Pioneer SX-727 Service Manual

8
.
ALIGNMENT PROCEDURE
The following alignments are required only in
very rare cases and should never be attempted
without the proper test equipment. Also, only
non-metallie tools must be used.
8-1 REQUIRED INSTRUMENTS
• Sweep generator: Center marker fre¬
quencies 10.7MHz, 455kHz
• Oscilloscope:
• AC VTVM
• AM/FM signal generator
• FM multiplex signal generator, preferably
with RF output
8-2 FM 10.7 MHz ALIGNMENT
1. Confirm +B voltage and current for 12V
±1V which should be 46mA to 50mA at
pin 4.
2. Disconnect leads from pins 22 (input)
and 24, then connect resistor 2.2kf2 as
shunted to pin 24 of FM/AM unit.
3. Connect 10.7MHz sweep generator to
pins 22 (hot) and 23 (ground) of FM/AM
unit. Set controls as follows:
Center frequency: 10.7MHz
Output: 55dB(500MV)
4. Connect vertical scope input to pin 24.
5. Align core of T1 for maximum gain and
symmetry to obtain scope pattern as in
Fig. 1.
6. Raise generator output gradually to 80dB
(lOmV), repeat step 5 realignment for
each output level, if necessary.
7. Disconnect one side of C23. Disconnect
oscilloscope and resistor 2.2kf2 from pin
24. Then reconnect lead to pin 24.
8. Connect scope input to pin 9.
9. Set generator output back to 55dB
(500/xV).
10. Adjust bottom core of T2 for maximum
gain and linearity.
Adjust top core so that center frequency
mark is located on zero axis, as shown in
Fig. 2.
11. Reconnect C23.
12. Reconnect input lead to pin 22.
8-3 FM FRONT END ALIGNMENT
1. Confirm +B current (drain 11mA ±4mA).
2. Connect FM signal generator output to
300J2 antenna input.
3. Connect AC VTVM to TAPE REC jack
on rear panel.
4. Adjust generator for 400Hz, 100% modu¬
lation.
5. Set SELECTOR switch on front panel to
FM MONO.
6. Adjust generator frequency and tuning
dial to 90MHz.
During the following adjustments, keep
the generator output as low as possible.
7. Adjust L4 core first, the adjust cores of
LI, L2, L3 for maximum reading on
VTVM and so that tuning meter indicates
center position (Fig. 3).
8. Set generator frequency and tuning dial
to 106MHz.
9. Adjust trimmer capacitor CT4 first, then
adjust CT1, CT2, CT3 for maximum
reading on VTVM.
10. Repeat these alignments several times
until satisfactory reading is obtained.
11. Finally, adjust T1 core for maximum
reading on VTVM.
8-4 FM MPX
DECODER ALIGNMENT
1. Set SELECTOR switch on front panel to
FM AUTO.
2. Connect RF output of FM multiplex
signal generator to 300£2 antenna input.
3. Adjust MPX generator as follows:
Signal Mode Deviation
L+R 40.5kHz
19kHz (pilot) 7.5kHz
4. Connect AC VTVM to TAPE REC jack
on rear panel.
5. Set generator signal mode to L-R (sub),
adjust core of T6 (located on FM/AM
unit) to obtain maximum reading on
VTVM.
6. Set generator signal mode to L. Adjust
VR2 (located on FM/AM unit) for mini¬
mum crosstalk on R channel TAPE REC
output.
7. Set generator signal mode to R. Repeat
above adjustment for minimum crosstalk
on L channel.
Fig. 1
-150kHz
+150kHz
Center frequency
Zero axis
12
Fig. 2