28HW-53 (serv.man20). Other power supply related faults — Sharp TV Technical Bulletin (repair manual)

Model
28HW-53 (serv.man20)
Pages
3 Few pages! See other manuals at the bottom of the first or last page.
Size
412.42 KB
Type
PDF
Document
Technical Bulletin
Brand
Device
TV / CTR / Other power supply related faults
File
28hw-53-sm20.pdf
Date

View Sharp 28HW-53 (serv.man20) Technical Bulletin online

CTV2003 04 07
Month of Issue:  
May 2003
        
Classification: 
White
TELEVISION TECHNICAL BULLETIN
Page 1 of 3
Sharp Electronics (UK) Limited
Reference JR29042003-3
Revision 2
White – Carry out as required
Yellow – Carry out as required and whenever the unit comes in for service
 Red – Carry out on all units
MODELS
56FW53H
59ESD7H
66FW53H
66FW54H
66ESD7H
76FW53H
76FW54H
28HW53H
66GF63H
66GF64H
76GF64H
No Operation
No operation can be caused by a number of components, the most common being around the primary control IC,
IC702.  If the supply on pin one of this IC falls below 5V, the operation of the power supply becomes unreliable (Note
that you will have to connect your meter ground to the negative end of the smoothing block).  As can be seen from the
previous circuit description, the supply circuit is fairly complex, however only a few components cause problems.  For
low supply voltage to IC702 check R770 (270
 safety) and R771 (470k
).  It has also been known for R721 and R703
(both 150k
) to fail causing a low 5V line.
IC707 (the secondary 5V regulator) can fail leading to a set that does not turn on, even though the power supply starts
up.  Normally its output goes low at around 3V.
No operation of the power supply or low HT (at about 30 to 40V) can be caused by R713 and R714 going high or
breaking down under load.  It is important that these two resistors are checked by substitution as they often read OK on
a meter, even though they are faulty.  Note that they should be metal film resistors and not carbon composition.
Erratic remote control operation
Erratic remote control operation has been traced to a number of components in the power supply.  Normally the faults
encountered are no remote control operation or intermittent control of the volume, either increasing dramatically or
rising slowly with the OSD visible.  D729 can cause these problems, but it is more common for noise to enter IC702 and
spurious remote control commands to be outputted to the microprocessor.  To prevent this happening fit a 470nF, 16V
SMD capacitor across the input of the optical diac – pins 1 and 3 of IC708 (see picture below).  The Sharp part number
for this capacitor is VCKYTV1CF474Z.  This capacitor was fitted during production of all GF and HW models.
Location of SMD Capacitor on IC708
CTV2003 04 07
Month of Issue:  
May 2003
        
Classification: 
White
TELEVISION TECHNICAL BULLETIN
Page 2 of 3
Sharp Electronics (UK) Limited
Reference JR29042003-3
Revision 2
White – Carry out as required
Yellow – Carry out as required and whenever the unit comes in for service
 Red – Carry out on all units
Intermittent Q701 failure
Intermittent failure of the chopper transistor can be caused by dry joints in the snubber circuit (C710, R715 and D711)
or poor connections on the main reservoir capacitor, C705.
Q701 has to be the correct type (S5F10N80A – Sharp part number RH-TX0198BMZZ), fitting the incorrect transistor
can lead to a power supply that does not work, causes excessive RF interference or is unreliable.  Note that this device
has been replaced by an alternative which requires D712 and R717 to be changed - see Technical Bulletin CTV 2002
12 01 for more details.
Input Circuit Failure
If there is a mains surge (or lightning strike) Q701 will invariably fail.  D712, Q702, Q703 and R716 will also have
suffered damage, as will the rectifier diodes (D701, D702, D703 and D704).  It is advisable to change all of these
components to prevent further failures, even if they are not faulty.
Low HT
IC706 can cause high or low HT.  It is a programmable zener diode that provides a stabilised voltage to the opto
coupler.  The Sharp part number for this device is RH-IX1704BMZZ.
Erratic Operation
Erratic operation of the processor (locking out, no control, etc) can be caused by the 3.3V rising to 5V due to one of the
components in the series regulator going faulty - Q710, Q711 or Q712.  Check for 3.3V on the emitter of Q712.
Pin
Name
I/O
Comment
DC Voltage
1
VDD
I
Supply
5.2V
2
OSCIN
I
Oscillator
2.5V
3
OSCOUT
O
Oscillator
2.5V
4
NMI
I
Remote input
5.0V
5
TEST
X
Grounded
0V
6
RESET
I
From  reset
5.2V
7
PB7
I
From processor
5.2V
8
PB6
I
100Hz reference
0.48V
9
PB5
I/O
Key scan
5.2V
10
PB3
I/O
Key scan
0V
11
PB1
I/O
Key scan
0V
12
PB0
I/O
Key scan
0V
13
PA3
O
To processor
5.2V
14
PA2
O
Degauss
0V
15
PA1
O
Power control
0V
16
VSS
X
Ground
0V
Q701 Gate Waveform and IC702 Voltage Table
Note that the above waveform has been taken on the primary side of the power supply.  It is therefore essential that an
isolation transformer be used in conjunction with the set.  This will ensure safe connection to the primary side reference.
This waveform will also change in pulse width depending upon the load demanded from the power supply.  The greater
the load the longer the on time.  The FET will switch on at about 4.5V, this is indicated as a short levelling off period on
the upward ramp.
CTV2003 04 07
Month of Issue:  
May 2003
        
Classification: 
White
TELEVISION TECHNICAL BULLETIN
Page 3 of 3
Sharp Electronics (UK) Limited
Reference JR29042003-3
Revision 2
White – Carry out as required
Yellow – Carry out as required and whenever the unit comes in for service
 Red – Carry out on all units
REF NO
DESCRIPTION
PART NUMBER
PRICE CODE
D701/2/3/4
Diode, RF2005
RH-DX0555BMZZ
AB
D729
Zener Diode, TZMC47
RH-EX0568BMZZ
AA
IC702
IC, ST6203B
RH-IX1646BMZZ
AL
IC703/4/5
IC, MOC8106SR2V-M
RH-IX0106BMZZ
AD
IC706
IC, KA431AZ
RH-IX1674BMZZ
AD
IC707
ICL4978
RH-IX1704BMZZ
AK
Q701
Transistor, S5F10N80A
RH-TX0198BMZZ
AU
Q702
Transistor, 2PD602AR
RH-TX0182BMZZ
AB
Q703
Transistor, 2SD2391Q
RH-TX0151BMZZ
AD
Q710
Transistor, 2SC2412
VS2SC2412KQ-1
AA
Q711
Transistor BC547
RH-TX0106BMZZ
AB
Q711
Transistor, BC547
TH-TX0106BMZZ
AB
Q712
Transistor, 2SC2412
VS2SC2412KQ-1
AA
R703
Resistor, 150k
 ½W SMD
VRD-RA2HD154J
AA
R713
Resistor, 560k
 ½W metal film
VRC-MA2HG564J
AA
R714
Resistor, 560k
 ½W metal film
VRC-MA2HG564J
AA
R716
Depends on model - refer to service manual parts listing
R721
Resistor, 150k
 ½W SMD
VRD-RA2HD154J
AA
R770
Resistor, 270
 ½W fusible
RR-XZ0229BMZZ
AA
R771
Resistor, 470k
 1W metal oxide
VRS-VV3AB474J
AA
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  • Schematics, wiring and block diagrams.
  • Printed wiring boards (PWB) and printed circuit boards (PCB).
  • Parts list (bill of materials).