Service Adjustment - Sharp 20CT-250 Service Manual

SERVICE ADJUSTMENT

115V ADJUSTMENT
No. Adjusting point Adjusting procedure/conditions
1 115V 1. Receive the Monoscope Pattern signal.
adjustment: 2. Set to the P-NORM mode.
R711 3. Connect a DC milliammeter between TP602(–)
and TP603(+).
4. Take the beam ammeter reading to make sure
that the beam current is between 900 µA and
1100 µA.
* If not, readjust the FBT screen control to ob-
tain the beam current of 900-1100 µA.
5. Connect a digital voltmeter to TP701.
6. Adjust R711 so that the digital voltmeter should
read 115 ±0.5 V.
PIF CHECKING
No. Adjusting point Adjusting procedure/conditions
1 Tuner IFT 1. Get the tuner ready to receive the E-9CH signal.
(preset): but with no signal input. Adjust the PLL data.
TU201 2. Connect the sweep generator's output cable to
the tuner antenna. (RF sweep)
3. Adjust the sweep generator's output level to 80
dBµV.
4. Connect the response lead (use a low-impedance
probe with wave detector; see Fig. 1 ) to the tun-
er's IF output terminal.
(This terminal must have the probe alone con-
nected.)
5. Set the RF AGC voltage to 0-6 V with no contact
with the waveform.
6. Adjust the tuner IF coil to obtain the waveform as
shown in Fig. 2 .
Note: Be sure to keep the tuner cover in posi-
tion during this adjustment.
Waveform and others
Waveform and others
IF-OUT
1000p
10kΩ
100kΩ
1000p
75Ω
Oscilloscope
Fig. 1
E-9CH
P C
– 1.5dB ± 0.8dB
Fig. 2
6-1
PIF/AFT/AGC ADJUSTMENT
No. Adjusting point Adjusting procedure/conditions
1 VCO adjust- 1. Disconnect the antenna from the tuner antenna
ment: T203 terminal.
2. Apply DC voltage to pin (4) of IC201 (IF AGC).
» DC voltage: 6.0 V (allowable +0.1 V)
3. Using a digital voltmeter, measure the DC volt-
age at pin (20)(PLL FIL) of IC201.
* The digital voltmeter must be able to take read-
ings down to the third decimal place.
4. Relieve pin (4) of IC201 of the DC voltage.
5. Reconnect the antenna in position and receive
the E-12CH signal. (With the AFT off, adjust the
receiving frequency to 224.25 MHz.)
6. Connect the DC digital voltmeter to pin (20) of
IC201. Adjust T203 so that the voltmeter should
read the same voltage as in Step 3.
Allowable error : 0.015 V (20 kHz)
2 AFT 1. Receive the PAL Colour Bar signal. If this signal
adjustment: is not available, any signal above the E-5CH band
T204 is acceptable.
» Field strength : 55-80 dBµV
Make sure the frequency is almost the same as
that of the received channel (±30 kHz).
2. Using the channel setting control, make a fre-
quency of 224.25 MHz appear on the screen (the
AFT turns off). If any other channel than Colour
Bar is received, make its frequency on the screen.
(The AFT turns off when the on-screen display
turns yellow.)
3. Turn T204 clockwise to have a 6V point, and
counterclockwise to have a 0.2V point. Position
the coil at the center of these two points.
4. Adjust T204 so that the DC voltage at pin (1) (AFT
OUT terminal) of IC201 be 3.3 ±0.1 V. (See Fig. 3 )
3 RF AGC 1. Receive the PAL Colour Bar signal.
» Field strength : 57 ±1 dBµV (75 ohms open)
cut-in
adjustment: 2. Connect the oscilloscope to TP210, as shown in
R216 Fig. 4 .
Oscilloscope
+
0.1V
–
Bias box
+
–
Fig. 4
3. Turn R216 to have the highest voltage.
4. Turn R216 slowly in the opposite direction until the
voltage goes down 0.1 V below the highest level.
5. Adjust the signal level to 63-67 dBµV and make
sure there is no noise.
6. Now adjust the signal level to 90-95 dBµV and make
sure there is no chrominance modulation beat.
Waveform and others
* Warm up the unit for longer than
10 minutes in advance.
* 10 kHz at about 0.007 V.
* Position the T203 core in the
range in which the Colour Bar
signal can be received.
DC voltage at TP201
6V
3.3V
DOWN A B' B B" C UP
Fig. 3
TV Set
TP210
» Bias box: About 4.5 V
6-2