Sharp 76GF-64H Service Manual ▷ View online
DA100 (50Hz) and DA50W Chassis – Repair Notes
Page 33 of 80
Figure 30: East/West Circuit – Print Side
Figure 31: East/West Circuit - Component Side
Sharp Electronics (UK) Limited - May 2003
Revision 3
DA100 (50Hz) and DA50W Chassis – Repair Notes
Page 34 of 80
Figure 32: East/West Drive Waveform - Pin 32 of IC801
It can be seen in the waveform that there are 'noise spikes' throughout the display. This is due to the
oscilloscope being used to record this picture. An analogue oscilloscope will display a smoother curve.
oscilloscope being used to record this picture. An analogue oscilloscope will display a smoother curve.
Sharp Electronics (UK) Limited - May 2003
Revision 3
DA100 (50Hz) and DA50W Chassis – Repair Notes
Page 35 of 80
Sharp Electronics (UK) Limited - May 2003
Revision 3
Faults in the East/West Circuit
When fault finding in the east/west circuit, it is important to ascertain in which part of the circuit the fault lies.
Check the control output of IC801 – pin 32. There should be a parabola waveform on this pin at a base frequency
of 50Hz. It will change wave shape depending upon the amount of correction applied, so it is important to enter
the service mode and ensure that none of the adjustments are at minimum or maximum.
If this waveform is present, and changes as adjustments are made, then the fault will lie in the drive or output
circuitry. Faults in this area include:
Check the control output of IC801 – pin 32. There should be a parabola waveform on this pin at a base frequency
of 50Hz. It will change wave shape depending upon the amount of correction applied, so it is important to enter
the service mode and ensure that none of the adjustments are at minimum or maximum.
If this waveform is present, and changes as adjustments are made, then the fault will lie in the drive or output
circuitry. Faults in this area include:
1. R519 going high or open circuit – it is a 100kΩ connected to the 150V supply.
2. Q506 going short, open or overheating – change L603, L604, D502, D503, D504, D516 and C528.
3. D603 and D604 going open or short-circuit.
4. Dry joint on C601 and/or C610.
2. Q506 going short, open or overheating – change L603, L604, D502, D503, D504, D516 and C528.
3. D603 and D604 going open or short-circuit.
4. Dry joint on C601 and/or C610.
If the waveform is not present, or is severely distorted, or the adjustment range is poor, then the fault could be
caused by the memory IC – IC1003 or the VDP - IC801. It is recommended that if this is the case, then the
NVM is blanked (see the NVM blanking section of this article) first. If this does not cure the problem, then it is
probable that IC801 is at fault.
Sometimes it will not be possible to set the geometry correctly in all modes after blanking he NVM. In this case
it will be necessary to ensure that the EPROM (IC1002) is correct as per the information given at the start of
this article. When the correct EPROM is fitted, the NVM will have to be blanked to enable the correct
information to be downloaded into it.
Replacement EPROM’s have been produced so that minimal geometry adjustments are required. If the picture
geometry is very poor after following the above procedure, the fault will be elsewhere in the east/west circuitry.
Reference Function
Part
Number
Comment
R519
Ramp charging resistor
VRD-RA2HD104J
Goes high or open – on component side of PWB
Q506
Eat/west output transistor
RH-TX0151BMZZ
Open or leaky – SMD
L603
Feed coil
RCLIP0286BMZZ
Low resistance – normally 8Ω
L604
Line earth return coil
RCLIP0284BMZZ
Low resistance
D502/3/4 Clamping
diodes
RH-DX0551BMZZ Intermittently
faulty
D516 Clamping
diode
RH-EX0837BMZZ Intermittently
faulty
C528 Reservoir
capacitor
VCEAGA1JW106M
Leaky
D603
East/west modulator diode
RH-DX0299BMZZ
Open or short circuit
D604
East/west modulator diode
RH-DX0302BMZZ
Open or short circuit
Notes
D516 is not shown on the GF circuit diagram, although it is fitted to the chassis.
R519 is sometimes a 150kΩ resistor, check the value before replacing, as fitting the incorrect value will result in
poor east/west geometry performance.
DA100 (50Hz) and DA50W Chassis – Repair Notes
Page 36 of 80
CRT PWB
There are two types of CRT PWB fitted to this chassis. One is for use with the 66cm and 76cm versions of this
chassis and the other is for the 56FW53H only. The major difference is that the 56cm model does not have a
scan velocity modulator or picture rotation circuits on this PWB. This means that it is physically smaller than the
other models.
Note that the CDA IC, IC1801, can be one of three types – see note in IC Identification section.
chassis and the other is for the 56FW53H only. The major difference is that the 56cm model does not have a
scan velocity modulator or picture rotation circuits on this PWB. This means that it is physically smaller than the
other models.
Note that the CDA IC, IC1801, can be one of three types – see note in IC Identification section.
Figure 33: 66cm and 76cm CRT PWB
Figure 34: 56FW53H CRT PWB
Faults on the CRT PWB
It is possible for the grey scale to wonder, picture brightness to ramp up or down. If the G2 is set correctly,
IC1801 is suspect. Check by substitution.
If the reference voltage on pin 2 of IC1801 is about 10V, picture smearing will occur. This is normally on the red
channel. If the voltage is below 9V the picture will blank. In both cases, Q912 or its associated components can
be responsible. This transistor can get hot during operation (especially on the GF models due to more current
being drawn through the device). If you suspect that the transistor may fail due to its temperature being too
high it is permissible to fit a 68Ω, 0.5W resistor between the collector and emitter of Q912. It is easier to fit
this resistor to the print side of the PWB.
IC1801 is suspect. Check by substitution.
If the reference voltage on pin 2 of IC1801 is about 10V, picture smearing will occur. This is normally on the red
channel. If the voltage is below 9V the picture will blank. In both cases, Q912 or its associated components can
be responsible. This transistor can get hot during operation (especially on the GF models due to more current
being drawn through the device). If you suspect that the transistor may fail due to its temperature being too
high it is permissible to fit a 68Ω, 0.5W resistor between the collector and emitter of Q912. It is easier to fit
this resistor to the print side of the PWB.
Sharp Electronics (UK) Limited - May 2003
Revision 3
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