PIF/AFT/SIF/AGC
ADJUSTMENT (Continued)
PIF
OVERALL WAVEFORM
1.
Set VT voltage at
5V
in
VH
band.
2.
Connect sweep generator’s output to the test
3.
4.
point of tuner.
l
Probe in use:
758
DC cut probe
l
Sweep output level:
70dB
Connect response lead to
TP401.
The response lead in use should be a direct
probe with a resistor of 1 Ok ohms included.
RF
AGC:
5.
Apply
approx.
4.OV
DC to the tuner
AGC
terminal.
PI F
AGC:
Apply
approx.
4.5V
DC to pin
(1)
of
IC1201
in IF
unit.
6.
7.
Connect a
120
ohm damping resistor in
parallel to
R1213
(in IF unit).
NOTE:
Cut the resistor’s leads as short as possible.
Turn off AFT:
8.
Adjust IF
AGC
voltage so that the output
waveform is of
approx.
lVp-p.
9.
Check that the overall waveform is as shown in
Figure below.
I
Adj-S
AFT is turned off if pin
(4)
of
IC1201
in IF unit is
grounded.
RF-AGC
CUT-IN CONTROL: R218
1.
Receive “PAL COLOUR BAR” signal with
colour
bar generator.
l
Signal strength:
53dB
,+
1dB
(with
75Q
terminated)
2.
Connect DC voltmeter to the tuner
AGC
terminal
(TP201).
(Full scale:
1OV)
3.
Turn
R218
so that the voltmeter reads the
maximum output.
4 Slowly turn
R218
in the opposite direction
until the voltmeter begins to decrease its
reading; then stop turning of
R218.
5.
Set the signal strength at
65dB
f
2dB,
and
check that no noise appears.
6.
Receive “MONOSCOPE PATTERN” signal, and
check that no noise appears.
l
Signal strength:
65dB
+,
2dB
7.
Set the signal strength at
90dB
to
95dB
and
check that there appears no crossmodulation
beating.
l
AGC
control value:
53dB
?
1
dB.
(with
75fi
terminated)
“NTSC”
4.5MHz
TRAP:
T201
1.
2.
3.
Receive “NTSC COLOUR BAR” signal with
colour
bar generator.
l
Signal strength:
Over 55dB, Below
80dB.
Connect
osci
I
loscope
to
TP40
1.
l
Voltage range:
O.SV/div.
l
Sweep time:
20psecYdiv.
l Synchronization: Horizontal sync.
Adjust
T201
so that the oscilloscope
waveform’s
920kHz
beat be minimum.
5
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