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DA100 (50Hz) and DA50W Chassis – Repair Notes
Page 25 of 80
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.
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 that R770 (270Ω safety) and R771 (470kΩ)
are OK. It has also been known for R721 and R703 (both 150kΩ) 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.
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.
IC702. If the supply on pin one of this IC falls below 5V, the operation of the power supply becomes unreliable.
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 that R770 (270Ω safety) and R771 (470kΩ)
are OK. It has also been known for R721 and R703 (both 150kΩ) 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.
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.
Other Problems in the Power Supply
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.
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.
Figure 21: Location of SMD Capacitor on IC708
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.
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.
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 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.
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.
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.
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 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.
Sharp Electronics (UK) Limited - May 2003
Revision 3
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