Sharp 76DW-18H (serv.man3) Service Manual ▷ View online
Wide Screen, Colour Television CW100 Chassis
Sharp Electronics (UK) Ltd
Technical Support
February 99
Page 9
The two transistors Q6701 and Q6702 comprise a Schmidt Trigger, which is triggered from the mains
input at double frequency, i.e. 100Hz. The square wave signal on pin 8 (PB6) is used to control the on
timer. This is necessary due to the fact that in standby, the Main Microprocessor, IC1001, is dormant,
i.e. no supply and therefore can not perform any functions. The off timer function is controlled within
IC1001.
input at double frequency, i.e. 100Hz. The square wave signal on pin 8 (PB6) is used to control the on
timer. This is necessary due to the fact that in standby, the Main Microprocessor, IC1001, is dormant,
i.e. no supply and therefore can not perform any functions. The off timer function is controlled within
IC1001.
Self Assessment Question
What is the default condition of IC6702 pin15?
If IC6702 pin15 is high, what will happen to the Dolby power supply?
What type of device is IC6702?
Wide Screen, Colour Television CW100 Chassis
Sharp Electronics (UK) Ltd
Technical Support
February 99
Page 10
Data Communications
45 Min Study Period
Wide Screen, Colour Television CW100 Chassis
Sharp Electronics (UK) Ltd
Technical Support
February 99
Page 11
MICROPROCESSOR CIRCUIT
This is possible the most complex processor circuit that has been used in a Sharp CTV’s, although it
is using the same processor as the CA10 chassis (the mask is different). The CW100 chassis has
several buses for communicating with all areas, which are:
is using the same processor as the CA10 chassis (the mask is different). The CW100 chassis has
several buses for communicating with all areas, which are:
Parallel bus
Communication between the Main Microprocessor and the EPROM
Two I
2
C buses,
SDA1 & SCA1, communicates with the 100Hz PWB, SCART PWB, Tuner &
MSP.
MSP.
SDA2 & SCA2, communicate with the NVM's.
M3 bus.
Communicates with the Megatext chip (similar to the CS chassis with the
addition of an Indent line)
addition of an Indent line)
‘D I C’ bus.
Communicates with the Dolby Processor circuit
Reset In.
Main system reset (IC1011).
Two reset out.
First '100Hz PWB Reset' is used by the 100Hz PWB, without this pulse the
line oscillator will not start.
line oscillator will not start.
Second 'Secondary Reset’ will reset the MSP, Megatext & the Dolby circuit.
Data In.
Data from Slave Processor, including remote control & keypad commands
Data Out.
Data to Slave Processor
There will be data on any of the buses if the Reset in & the 100Hz reset have not occurred.
Figure 1 - Reset Pulse Timing
100Hz PWB
Reset
Reset
Secondary
Reset
Reset
Main Reset
5V Supply
0V
5V
5V
5V
5V
0V
0V
0V
Line Oscillator Start
Wide Screen, Colour Television CW100 Chassis
Sharp Electronics (UK) Ltd
Technical Support
February 99
Page 12
Once the main system microprocessor, IC1001, has been reset and the clock oscillator is running at
the correct frequency the internal programme sequence is initiated. It first checks that the internal
functions of the IC are working correctly then checks the devices connected to it via the I
the correct frequency the internal programme sequence is initiated. It first checks that the internal
functions of the IC are working correctly then checks the devices connected to it via the I
2
C bus. If any
errors are encountered then the microprocessor will shut down (no line drive and the NICAM LED is
turned on or pulsing); or fault symptom of pulsating line drive.
turned on or pulsing); or fault symptom of pulsating line drive.
Figure 2 - CPU Data Communication (CA10)
P
ROTECTION CIRCUITS
There is protection input on IC1001, pin 78 (PROT) which causes the set to switch to standby should
there be a fault with the centre audio channel or excessive beam current. Pin 78 is active low
therefore, if the beam current increases in a negative direction D627 (47V zener) will conduct, taking
pin78 low, initiating a standby command. Q709, Q710 & Q711 are normally biased off and are part of
an averaging circuit. The input to this circuit comes from the Audio Centre Channel Output Stage. The
average of a sine wave is zero, it the average goes positive Q709 will turn on taking pin 78 low. If the
average goes negative Q710 will turn on feeding –19V to the emitter of Q711. Since Q711 base is
grounded, Q711 will turn on taking pin 78 low. In both cases, if the average of the sine wave is not
zero pin 78 will go low initiating a standby command.
there be a fault with the centre audio channel or excessive beam current. Pin 78 is active low
therefore, if the beam current increases in a negative direction D627 (47V zener) will conduct, taking
pin78 low, initiating a standby command. Q709, Q710 & Q711 are normally biased off and are part of
an averaging circuit. The input to this circuit comes from the Audio Centre Channel Output Stage. The
average of a sine wave is zero, it the average goes positive Q709 will turn on taking pin 78 low. If the
average goes negative Q710 will turn on feeding –19V to the emitter of Q711. Since Q711 base is
grounded, Q711 will turn on taking pin 78 low. In both cases, if the average of the sine wave is not
zero pin 78 will go low initiating a standby command.
100Hz
Scart
MSP
Tuner
I2C
I2C
Address
Data
M3
Megatext
NVM
NVM
Eprom
Reset
Microprocessor
Slave
processor
processor
Standby
Remote
Control
Control
Front
CH & Vol keys
CH & Vol keys
Protection
-19V
ABL
Audio centre
Channel
Channel
5V
Reset
5V
DRAM
RAM
DSP
APU
D
I
C
D
D
C
C
I
I
Reset
IF
AFT (IC202)
Q709
Q710
Q711
D627
Click on the first or last page to see other 76DW-18H (serv.man3) service manuals if exist.