Sharp 20CT-250, Service Manual

Page: 15 / 30

15
15-1 15-2
20CT
-250
TROUBLE SHOOTING TABLE
NO RASTER
Blown out.
Replace the fuse.
Check Q701 and IC751.
Abnormal
YES
YES
NO
ON/OFF ON
NO
Abnormal
The fuse is again blown out.
Horizontal circuit oscillate ?
Check Q1005, Q1006,
IC603 and IC801.
D1013 (Power LED Red)
turns on or turns ON/OFF.
Check T701 pin (1) voltage
(Approx. 310V at 220V AC)
Check C707, D701, D702,
D703 and D704.
Check F701.
Normal
Normal
Check Secondary Main+B
(Approx. 115V)
Normal
Normal Abnormal
Normal
Check CRT connector K1-
K5 bias.
Check
C866 and
L851.
Check
IC801
Bus error
mode.
See
Fig. 1
or Check
IC602.
Checking the
protector circuit
(The protector
circuit still works
even if there is no
vertical waveform
at pin (2) of IC1001.)
Check R609 and R611.
D1013 (Power LED Green)
turns on.
Check D708 and D732.
Check R702 and D709.
Normal
If a bus error happens, the LED RED (pin 3) indicator starts flashing and the power
is turned off. The power key is still effective.
IC1003
EEPROM (ST24C04)
IC801
V/C/J (TB1226DN)
TU201
PLL (N0004KJ)
2s 0.5s
Fig. 1
TROUBLE SHOOTING TABLE
(Continued)
NO PICTURE, NO SOUND
YES
YES
YES
(Signal)
NO
YES
(Noise)
NO
NO
Does noise or signal appear
at pin (13) of IC201 ?
NO SOUND
No snow noise.
Does noise or signal appear at pin (21)
of IC201 ?
Noise increases but no signal is
received.
Check the tuner supply voltage MB
must be approx, 9V. BP must approx.
5V. BT must be approx, 31V. And CH
preset data check.
Check the tuner AGC.
Normal
Normal Abnormal
Does noise or
signal appear at
pin (1) of IC801 ? Check PIF circuits
and its related
parts.
Check IC801.
Check A/V sw
circuits (IC401).
Check IC201.
Check the tuner
circuit.
Does the noise level increase at max.
Contrast, Brightness and Sound controls ?
CIRCUITS TO BE CHECKED:
»
Tuner.
»
PIF.
»
Automatic Gain Control.
»
(5V), (9V) Power Source.
CIRCUITS TO BE CHECKED:
»
SIF Amplifier Circuit.
»
Sound Detector Circuit.
»
Sound Switch and Att. Control.
»
Audio Output Circuit.
YES
NO
YES
NO
Does signal appear at pin
(1) and (8) of IC302 ?
Does signal appear at pin
(3) of IC351 ?
Check pin (5) of IC351 and
peripheral circuit.
Check IC201 and peripheral
circuit.
Check pin (14), (15) of
IC201.
Check Q207 and peripheral
circuit.
Check IC302 and peripheral
circuit.