Sharp 25WG3, Service Manual

Page: 7 / 44

7
25WG3
SER
VICE ADJUSTMENT
NO
ADJUSTMENT POINT
WAVEFORM OR OTHERS
1
VCO ADJUSTMENT (I
2
C BUS CONTR
OL)
1.
Receiv
e E-10CH (210.25MHz) "P
AL
COLOUR BAR" signal.
2.
Call "A
UT
O
VCO" in SER
VICE mode
. If
the Channel frequency displa
ys on
screen is 210.20MHz, skip (3), (4) & (5) steps
.
3.
Press FUNCTION b
utton to call
"DIRECT FREQ IN".
4.
Push "2", "1", "0", "2", "0".
5.
Then Press FUNCTION again.
6.
Press
V
olume UP to r
un "A
UT
O
VCO".
Once finishing, "OK" message displa
y
on screen.
Signal Strength: 60 ~ 70 dB
2
A
GC ADJUSTMENT
(I
2
C BUS CONTR
OL)
7.
Receiv
e E-12CH (P
AL COLOR BAR) signal.
Signal strength : 57
±
1 dB ( 75ohm open)
8.
Connect the oscilloscope to P201 (T
uner’
s A
GC
T
e
rminal) as sho
wn in
Figure 1.
Figure 1
9.
Call "A
GC" in SER
VICE mode
.
10.
Increase or decrease "A
GC" b
y
using
V
olume so that obtain the highest
V
oltage
.
11.
Press
V
olume slo
wly in the opposite
direction until the v
oltage drops 0.1V ~
0.3V lo
w
er than the highest le
v
el.
12.
Change the antenna input signal to 63 ~ 67dB
µ
V
, and mak
e sure there is no
noise
.
13.
T
u
rn
up the input signal to 90 ~ 95 dB
µ
V
to be sure that there is no cross modulation beat.
ADJUSTMENT CONDITION/PROCEDURE
VCO
, AND A
GC ADJUSTMENT
SOUND ADJUSTMENT
2
SP SUB
V
OLUME
(I
2
C BUS CONTR
OL)
5.
Receiv
e "COLOUR BAR" signal.
A
udio signal:
400Hz, 100%
modulation.
(50kHz de
v.
)
6.
Connect Dumm
y load* to P3304.
7.
Connect
VTVM’
s probe to the P3304.
(1 R, 2 GND
, 3 GND
, 4 L, 5 NIL, 6 NIL
7 NIL 8 NIL)
8.
Call the "SP SUB
V
OL" in the SER
VICE
mode
.
9.
Increase or decrease "SP SUB
V
OL" b
y
using
V
olume UP/DO
WN k
e
y,
so that
the
VTVM should read the v
alue*.
3
NOISE MUTE CHECKING
10.
Receiv
e the 400Hz modulated signal.
11.
T
u
rn
up the v
olume control to Maxim
um
and mak
e sure the sound is heard from
the speak
ers
. Then put the unit in the
no-signal state
.
12.
Be sure that the sound m
ute is eff
ectiv
e
.
13.
Finally tur
n do
wn the v
olume control to
minim
um.
NO
ADJUSTMENT POINT
WAVEFORM OR OTHERS
1
RF SUB
V
OLUME
(I
2
C BUS CONTR
OL)
1.
Receiv
e "P
AL COLOUR BAR" signal.
A
udio signal:
400 Hz, 100% modulated
(50kHz de
v.
)
2.
Connect the Oscilloscope to the A
udio
Out (L or R) ter
minal.
(T
er
minate with
10k ohm impendence).
3.
Call the "RF SUB
V
OL" in SER
VICE
mode
.
4.
Increase or decrease "RF SUB
V
OL" b
y
using
V
olume UP/DO
WN k
e
y,
so that
the 400Hz sine w
a
v
e
be 1.76Vp-p
.
T
olerence:
1.76
Vp-p
±
0.10
Vp-p
.
ADJUSTMENT CONDITION/PROCEDURE
OSCILLOSCOPE
TV SET
BIAS BOX : ABOUT 4.5V
P201
+
-
+
-
1
2
*
Note :
T
e
rminated 8 ohm
to get 7.75
±
0.1Vr
ms
.
(L Channel)